1 # SOME DESCRIPTIVE TITLE
2 # Copyright (C) YEAR Free Software Foundation, Inc.
3 # This file is distributed under the same license as the PACKAGE package.
4 # FIRST AUTHOR <EMAIL@ADDRESS>, YEAR.
9 "Project-Id-Version: PACKAGE VERSION\n"
10 "POT-Creation-Date: 2015-02-04 23:33+0900\n"
11 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
12 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
13 "Language-Team: LANGUAGE <LL@li.org>\n"
16 "Content-Type: text/plain; charset=UTF-8\n"
17 "Content-Transfer-Encoding: 8bit\n"
20 #: build/C/man3/sem_close.3:26
26 #: build/C/man3/sem_close.3:26 build/C/man3/sem_open.3:26 build/C/man7/sem_overview.7:26
32 #: build/C/man3/sem_close.3:26 build/C/man3/sem_destroy.3:26 build/C/man3/sem_getvalue.3:26 build/C/man3/sem_init.3:26 build/C/man3/sem_open.3:26 build/C/man7/sem_overview.7:26 build/C/man3/sem_post.3:26 build/C/man3/sem_unlink.3:26 build/C/man3/sem_wait.3:26 build/C/man2/semctl.2:41 build/C/man2/semget.2:36 build/C/man2/semop.2:35
38 #: build/C/man3/sem_close.3:26 build/C/man3/sem_destroy.3:26 build/C/man3/sem_getvalue.3:26 build/C/man3/sem_init.3:26 build/C/man3/sem_open.3:26 build/C/man7/sem_overview.7:26 build/C/man3/sem_post.3:26 build/C/man3/sem_unlink.3:26 build/C/man3/sem_wait.3:26 build/C/man2/semctl.2:41 build/C/man2/semget.2:36 build/C/man2/semop.2:35
40 msgid "Linux Programmer's Manual"
44 #: build/C/man3/sem_close.3:27 build/C/man3/sem_destroy.3:27 build/C/man3/sem_getvalue.3:27 build/C/man3/sem_init.3:27 build/C/man3/sem_open.3:27 build/C/man7/sem_overview.7:27 build/C/man3/sem_post.3:27 build/C/man3/sem_unlink.3:27 build/C/man3/sem_wait.3:27 build/C/man2/semctl.2:42 build/C/man2/semget.2:37 build/C/man2/semop.2:36
50 #: build/C/man3/sem_close.3:29
51 msgid "sem_close - close a named semaphore"
55 #: build/C/man3/sem_close.3:29 build/C/man3/sem_destroy.3:29 build/C/man3/sem_getvalue.3:29 build/C/man3/sem_init.3:29 build/C/man3/sem_open.3:29 build/C/man3/sem_post.3:29 build/C/man3/sem_unlink.3:29 build/C/man3/sem_wait.3:29 build/C/man2/semctl.2:44 build/C/man2/semget.2:39 build/C/man2/semop.2:38
61 #: build/C/man3/sem_close.3:32 build/C/man3/sem_destroy.3:32 build/C/man3/sem_getvalue.3:32 build/C/man3/sem_init.3:32 build/C/man3/sem_post.3:32 build/C/man3/sem_unlink.3:32 build/C/man3/sem_wait.3:32
63 msgid "B<#include E<lt>semaphore.hE<gt>>\n"
67 #: build/C/man3/sem_close.3:34
69 msgid "B<int sem_close(sem_t *>I<sem>B<);>\n"
73 #: build/C/man3/sem_close.3:37 build/C/man3/sem_destroy.3:37 build/C/man3/sem_getvalue.3:37 build/C/man3/sem_init.3:37 build/C/man3/sem_open.3:41 build/C/man3/sem_post.3:37 build/C/man3/sem_unlink.3:37 build/C/man3/sem_wait.3:41
74 msgid "Link with I<-pthread>."
78 #: build/C/man3/sem_close.3:37 build/C/man3/sem_destroy.3:37 build/C/man3/sem_getvalue.3:37 build/C/man3/sem_init.3:37 build/C/man3/sem_open.3:41 build/C/man7/sem_overview.7:29 build/C/man3/sem_post.3:37 build/C/man3/sem_unlink.3:37 build/C/man3/sem_wait.3:49 build/C/man2/semctl.2:52 build/C/man2/semget.2:49 build/C/man2/semop.2:57
84 #: build/C/man3/sem_close.3:43
86 "B<sem_close>() closes the named semaphore referred to by I<sem>, allowing "
87 "any resources that the system has allocated to the calling process for this "
88 "semaphore to be freed."
92 #: build/C/man3/sem_close.3:43 build/C/man3/sem_destroy.3:55 build/C/man3/sem_getvalue.3:54 build/C/man3/sem_init.3:77 build/C/man3/sem_open.3:104 build/C/man3/sem_post.3:45 build/C/man3/sem_unlink.3:44 build/C/man3/sem_wait.3:108 build/C/man2/semctl.2:340 build/C/man2/semget.2:147 build/C/man2/semop.2:298
98 #: build/C/man3/sem_close.3:49
100 "On success B<sem_close>() returns 0; on error, -1 is returned, with "
101 "I<errno> set to indicate the error."
105 #: build/C/man3/sem_close.3:49 build/C/man3/sem_destroy.3:61 build/C/man3/sem_getvalue.3:60 build/C/man3/sem_init.3:83 build/C/man3/sem_open.3:116 build/C/man3/sem_post.3:52 build/C/man3/sem_unlink.3:50 build/C/man3/sem_wait.3:114 build/C/man2/semctl.2:387 build/C/man2/semget.2:153 build/C/man2/semop.2:308
111 #: build/C/man3/sem_close.3:50 build/C/man3/sem_destroy.3:62 build/C/man3/sem_getvalue.3:61 build/C/man3/sem_init.3:84 build/C/man3/sem_open.3:132 build/C/man3/sem_open.3:137 build/C/man3/sem_post.3:53 build/C/man3/sem_wait.3:119 build/C/man3/sem_wait.3:133 build/C/man2/semctl.2:420 build/C/man2/semget.2:177 build/C/man2/semget.2:183 build/C/man2/semop.2:356
117 #: build/C/man3/sem_close.3:54 build/C/man3/sem_destroy.3:66 build/C/man3/sem_getvalue.3:65 build/C/man3/sem_post.3:57 build/C/man3/sem_wait.3:123
118 msgid "I<sem> is not a valid semaphore."
122 #: build/C/man3/sem_close.3:54 build/C/man3/sem_destroy.3:71 build/C/man3/sem_getvalue.3:70 build/C/man3/sem_init.3:100 build/C/man3/sem_open.3:170 build/C/man7/sem_overview.7:138 build/C/man3/sem_post.3:66 build/C/man3/sem_unlink.3:67 build/C/man3/sem_wait.3:151 build/C/man2/semctl.2:462 build/C/man2/semget.2:210 build/C/man2/semop.2:386
124 msgid "CONFORMING TO"
128 #: build/C/man3/sem_close.3:56 build/C/man3/sem_destroy.3:73 build/C/man3/sem_getvalue.3:72 build/C/man3/sem_init.3:102 build/C/man3/sem_open.3:172 build/C/man7/sem_overview.7:140 build/C/man3/sem_post.3:68 build/C/man3/sem_unlink.3:69 build/C/man3/sem_wait.3:153
129 msgid "POSIX.1-2001."
133 #: build/C/man3/sem_close.3:56 build/C/man3/sem_destroy.3:73 build/C/man3/sem_getvalue.3:72 build/C/man3/sem_init.3:102 build/C/man7/sem_overview.7:140 build/C/man3/sem_post.3:68 build/C/man3/sem_wait.3:153 build/C/man2/semctl.2:476 build/C/man2/semget.2:214 build/C/man2/semop.2:389
139 #: build/C/man3/sem_close.3:60
141 "All open named semaphores are automatically closed on process termination, "
142 "or upon B<execve>(2)."
146 #: build/C/man3/sem_close.3:60 build/C/man3/sem_destroy.3:79 build/C/man3/sem_getvalue.3:76 build/C/man3/sem_init.3:107 build/C/man3/sem_open.3:172 build/C/man7/sem_overview.7:152 build/C/man3/sem_post.3:75 build/C/man3/sem_unlink.3:69 build/C/man3/sem_wait.3:270 build/C/man2/semctl.2:536 build/C/man2/semget.2:296 build/C/man2/semop.2:533
152 #: build/C/man3/sem_close.3:67
154 "B<sem_getvalue>(3), B<sem_open>(3), B<sem_post>(3), B<sem_unlink>(3), "
155 "B<sem_wait>(3), B<sem_overview>(7)"
159 #: build/C/man3/sem_close.3:67 build/C/man3/sem_destroy.3:84 build/C/man3/sem_getvalue.3:80 build/C/man3/sem_init.3:112 build/C/man3/sem_open.3:179 build/C/man7/sem_overview.7:162 build/C/man3/sem_post.3:79 build/C/man3/sem_unlink.3:75 build/C/man3/sem_wait.3:276 build/C/man2/semctl.2:543 build/C/man2/semget.2:303 build/C/man2/semop.2:542
165 #: build/C/man3/sem_close.3:75 build/C/man3/sem_destroy.3:92 build/C/man3/sem_getvalue.3:88 build/C/man3/sem_init.3:120 build/C/man3/sem_open.3:187 build/C/man7/sem_overview.7:170 build/C/man3/sem_post.3:87 build/C/man3/sem_unlink.3:83 build/C/man3/sem_wait.3:284 build/C/man2/semctl.2:551 build/C/man2/semget.2:311 build/C/man2/semop.2:550
167 "This page is part of release 3.79 of the Linux I<man-pages> project. A "
168 "description of the project, information about reporting bugs, and the latest "
169 "version of this page, can be found at "
170 "\\%http://www.kernel.org/doc/man-pages/."
174 #: build/C/man3/sem_destroy.3:26
180 #: build/C/man3/sem_destroy.3:26 build/C/man3/sem_getvalue.3:26
186 #: build/C/man3/sem_destroy.3:29
187 msgid "sem_destroy - destroy an unnamed semaphore"
191 #: build/C/man3/sem_destroy.3:34
193 msgid "B<int sem_destroy(sem_t *>I<sem>B<);>\n"
197 #: build/C/man3/sem_destroy.3:41
199 "B<sem_destroy>() destroys the unnamed semaphore at the address pointed to "
204 #: build/C/man3/sem_destroy.3:46
206 "Only a semaphore that has been initialized by B<sem_init>(3) should be "
207 "destroyed using B<sem_destroy>()."
211 #: build/C/man3/sem_destroy.3:51
213 "Destroying a semaphore that other processes or threads are currently blocked "
214 "on (in B<sem_wait>(3)) produces undefined behavior."
218 #: build/C/man3/sem_destroy.3:55
220 "Using a semaphore that has been destroyed produces undefined results, until "
221 "the semaphore has been reinitialized using B<sem_init>(3)."
225 #: build/C/man3/sem_destroy.3:61
227 "B<sem_destroy>() returns 0 on success; on error, -1 is returned, and "
228 "I<errno> is set to indicate the error."
232 #: build/C/man3/sem_destroy.3:66 build/C/man3/sem_getvalue.3:65 build/C/man3/sem_init.3:95 build/C/man3/sem_post.3:61 build/C/man3/sem_unlink.3:62 build/C/man3/sem_wait.3:143
238 #: build/C/man3/sem_destroy.3:67 build/C/man3/sem_getvalue.3:66 build/C/man3/sem_init.3:96 build/C/man3/sem_post.3:62 build/C/man3/sem_unlink.3:63 build/C/man3/sem_wait.3:144
240 msgid "Multithreading (see pthreads(7))"
244 #: build/C/man3/sem_destroy.3:71
245 msgid "The B<sem_destroy>() function is thread-safe."
248 #. But not on NPTL, where sem_destroy () is a no-op..
250 #: build/C/man3/sem_destroy.3:79
252 "An unnamed semaphore should be destroyed with B<sem_destroy>() before the "
253 "memory in which it is located is deallocated. Failure to do this can result "
254 "in resource leaks on some implementations."
258 #: build/C/man3/sem_destroy.3:84
259 msgid "B<sem_init>(3), B<sem_post>(3), B<sem_wait>(3), B<sem_overview>(7)"
263 #: build/C/man3/sem_getvalue.3:26
269 #: build/C/man3/sem_getvalue.3:29
270 msgid "sem_getvalue - get the value of a semaphore"
274 #: build/C/man3/sem_getvalue.3:34
276 msgid "B<int sem_getvalue(sem_t *>I<sem>B<, int *>I<sval>B<);>\n"
280 #: build/C/man3/sem_getvalue.3:43
282 "B<sem_getvalue>() places the current value of the semaphore pointed to "
283 "I<sem> into the integer pointed to by I<sval>."
287 #: build/C/man3/sem_getvalue.3:54
289 "If one or more processes or threads are blocked waiting to lock the "
290 "semaphore with B<sem_wait>(3), POSIX.1-2001 permits two possibilities for "
291 "the value returned in I<sval>: either 0 is returned; or a negative number "
292 "whose absolute value is the count of the number of processes and threads "
293 "currently blocked in B<sem_wait>(3). Linux adopts the former behavior."
297 #: build/C/man3/sem_getvalue.3:60
299 "B<sem_getvalue>() returns 0 on success; on error, -1 is returned and "
300 "I<errno> is set to indicate the error."
304 #: build/C/man3/sem_getvalue.3:70
305 msgid "The B<sem_getvalue>() function is thread-safe."
309 #: build/C/man3/sem_getvalue.3:76
311 "The value of the semaphore may already have changed by the time "
312 "B<sem_getvalue>() returns."
316 #: build/C/man3/sem_getvalue.3:80
317 msgid "B<sem_post>(3), B<sem_wait>(3), B<sem_overview>(7)"
321 #: build/C/man3/sem_init.3:26
327 #: build/C/man3/sem_init.3:26
333 #: build/C/man3/sem_init.3:29
334 msgid "sem_init - initialize an unnamed semaphore"
338 #: build/C/man3/sem_init.3:34
341 "B<int sem_init(sem_t *>I<sem>B<, int >I<pshared>B<, unsigned int "
346 #: build/C/man3/sem_init.3:44
348 "B<sem_init>() initializes the unnamed semaphore at the address pointed to "
349 "by I<sem>. The I<value> argument specifies the initial value for the "
354 #: build/C/man3/sem_init.3:49
356 "The I<pshared> argument indicates whether this semaphore is to be shared "
357 "between the threads of a process, or between processes."
361 #: build/C/man3/sem_init.3:57
363 "If I<pshared> has the value 0, then the semaphore is shared between the "
364 "threads of a process, and should be located at some address that is visible "
365 "to all threads (e.g., a global variable, or a variable allocated dynamically "
370 #: build/C/man3/sem_init.3:74
372 "If I<pshared> is nonzero, then the semaphore is shared between processes, "
373 "and should be located in a region of shared memory (see B<shm_open>(3), "
374 "B<mmap>(2), and B<shmget>(2)). (Since a child created by B<fork>(2) "
375 "inherits its parent's memory mappings, it can also access the semaphore.) "
376 "Any process that can access the shared memory region can operate on the "
377 "semaphore using B<sem_post>(3), B<sem_wait>(3), and so on."
381 #: build/C/man3/sem_init.3:77
383 "Initializing a semaphore that has already been initialized results in "
384 "undefined behavior."
388 #: build/C/man3/sem_init.3:83
390 "B<sem_init>() returns 0 on success; on error, -1 is returned, and I<errno> "
391 "is set to indicate the error."
395 #: build/C/man3/sem_init.3:89
396 msgid "I<value> exceeds B<SEM_VALUE_MAX>."
400 #: build/C/man3/sem_init.3:89
406 #: build/C/man3/sem_init.3:95
408 "I<pshared> is nonzero, but the system does not support process-shared "
409 "semaphores (see B<sem_overview>(7))."
413 #: build/C/man3/sem_init.3:100
414 msgid "The B<sem_init>() function is thread-safe."
418 #: build/C/man3/sem_init.3:107
420 "Bizarrely, POSIX.1-2001 does not specify the value that should be returned "
421 "by a successful call to B<sem_init>(). POSIX.1-2008 rectifies this, "
422 "specifying the zero return on success."
426 #: build/C/man3/sem_init.3:112
427 msgid "B<sem_destroy>(3), B<sem_post>(3), B<sem_wait>(3), B<sem_overview>(7)"
431 #: build/C/man3/sem_open.3:26
437 #: build/C/man3/sem_open.3:29
438 msgid "sem_open - initialize and open a named semaphore"
442 #: build/C/man3/sem_open.3:34
445 "B<#include E<lt>fcntl.hE<gt>> /* For O_* constants */\n"
446 "B<#include E<lt>sys/stat.hE<gt>> /* For mode constants */\n"
447 "B<#include E<lt>semaphore.hE<gt>>\n"
451 #: build/C/man3/sem_open.3:38
454 "B<sem_t *sem_open(const char *>I<name>B<, int >I<oflag>B<);>\n"
455 "B<sem_t *sem_open(const char *>I<name>B<, int >I<oflag>B<, >\n"
456 "B< mode_t >I<mode>B<, unsigned int >I<value>B<);>\n"
460 #: build/C/man3/sem_open.3:50
462 "B<sem_open>() creates a new POSIX semaphore or opens an existing "
463 "semaphore. The semaphore is identified by I<name>. For details of the "
464 "construction of I<name>, see B<sem_overview>(7)."
467 #. In reality the filesystem IDs are used on Linux.
469 #: build/C/man3/sem_open.3:76
471 "The I<oflag> argument specifies flags that control the operation of the "
472 "call. (Definitions of the flags values can be obtained by including "
473 "I<E<lt>fcntl.hE<gt>>.) If B<O_CREAT> is specified in I<oflag>, then the "
474 "semaphore is created if it does not already exist. The owner (user ID) of "
475 "the semaphore is set to the effective user ID of the calling process. The "
476 "group ownership (group ID) is set to the effective group ID of the calling "
477 "process. If both B<O_CREAT> and B<O_EXCL> are specified in I<oflag>, then "
478 "an error is returned if a semaphore with the given I<name> already exists."
482 #: build/C/man3/sem_open.3:104
484 "If B<O_CREAT> is specified in I<oflag>, then two additional arguments must "
485 "be supplied. The I<mode> argument specifies the permissions to be placed on "
486 "the new semaphore, as for B<open>(2). (Symbolic definitions for the "
487 "permissions bits can be obtained by including I<E<lt>sys/stat.hE<gt>>.) The "
488 "permissions settings are masked against the process umask. Both read and "
489 "write permission should be granted to each class of user that will access "
490 "the semaphore. The I<value> argument specifies the initial value for the "
491 "new semaphore. If B<O_CREAT> is specified, and a semaphore with the given "
492 "I<name> already exists, then I<mode> and I<value> are ignored."
496 #: build/C/man3/sem_open.3:116
498 "On success, B<sem_open>() returns the address of the new semaphore; this "
499 "address is used when calling other semaphore-related functions. On error, "
500 "B<sem_open>() returns B<SEM_FAILED>, with I<errno> set to indicate the "
505 #: build/C/man3/sem_open.3:117 build/C/man3/sem_unlink.3:51 build/C/man2/semctl.2:391 build/C/man2/semget.2:157 build/C/man2/semop.2:320
511 #: build/C/man3/sem_open.3:121
512 msgid "The semaphore exists, but the caller does not have permission to open it."
516 #: build/C/man3/sem_open.3:121 build/C/man2/semget.2:165
522 #: build/C/man3/sem_open.3:132
524 "Both B<O_CREAT> and B<O_EXCL> were specified in I<oflag>, but a semaphore "
525 "with this I<name> already exists."
529 #: build/C/man3/sem_open.3:137
530 msgid "I<value> was greater than B<SEM_VALUE_MAX>."
534 #: build/C/man3/sem_open.3:141
535 msgid "I<name> consists of just \"/\", followed by no other characters."
539 #: build/C/man3/sem_open.3:141
545 #: build/C/man3/sem_open.3:144
546 msgid "The process already has the maximum number of files and open."
550 #: build/C/man3/sem_open.3:144 build/C/man3/sem_unlink.3:54
552 msgid "B<ENAMETOOLONG>"
556 #: build/C/man3/sem_open.3:148 build/C/man3/sem_unlink.3:58
557 msgid "I<name> was too long."
561 #: build/C/man3/sem_open.3:148
567 #: build/C/man3/sem_open.3:151
568 msgid "The system limit on the total number of open files has been reached."
572 #: build/C/man3/sem_open.3:151 build/C/man3/sem_unlink.3:58 build/C/man2/semget.2:190
577 #. this error can occur if we have a name of the (nonportable) form
578 #. /dir/name, and the directory /dev/shm/dir does not exist.
580 #: build/C/man3/sem_open.3:167
582 "The B<O_CREAT> flag was not specified in I<oflag> and no semaphore with this "
583 "I<name> exists; or, B<O_CREAT> was specified, but I<name> wasn't well "
588 #: build/C/man3/sem_open.3:167 build/C/man2/semget.2:198 build/C/man2/semop.2:363
594 #: build/C/man3/sem_open.3:170
595 msgid "Insufficient memory."
599 #: build/C/man3/sem_open.3:179
601 "B<sem_close>(3), B<sem_getvalue>(3), B<sem_post>(3), B<sem_unlink>(3), "
602 "B<sem_wait>(3), B<sem_overview>(7)"
606 #: build/C/man7/sem_overview.7:26
612 #: build/C/man7/sem_overview.7:29
613 msgid "sem_overview - overview of POSIX semaphores"
617 #: build/C/man7/sem_overview.7:31
618 msgid "POSIX semaphores allow processes and threads to synchronize their actions."
622 #: build/C/man7/sem_overview.7:41
624 "A semaphore is an integer whose value is never allowed to fall below zero. "
625 "Two operations can be performed on semaphores: increment the semaphore value "
626 "by one (B<sem_post>(3)); and decrement the semaphore value by one "
627 "(B<sem_wait>(3)). If the value of a semaphore is currently zero, then a "
628 "B<sem_wait>(3) operation will block until the value becomes greater than "
633 #: build/C/man7/sem_overview.7:44
634 msgid "POSIX semaphores come in two forms: named semaphores and unnamed semaphores."
638 #: build/C/man7/sem_overview.7:44
640 msgid "B<Named semaphores>"
643 #. glibc allows the initial slash to be omitted, and makes
644 #. multiple initial slashes equivalent to a single slash.
645 #. This differs from the implementation of POSIX message queues.
646 #. glibc allows subdirectory components in the name, in which
647 #. case the subdirectory tree must exist under /dev/shm, and
648 #. the fist subdirectory component must exist as the name
649 #. sem.name, and all of the subdirectory components must allow the
650 #. required permissions if a user wants to create a semaphore
651 #. object in a subdirectory.
653 #: build/C/man7/sem_overview.7:64
655 "A named semaphore is identified by a name of the form I</somename>; that is, "
656 "a null-terminated string of up to B<NAME_MAX>I<-4> (i.e., 251) characters "
657 "consisting of an initial slash, followed by one or more characters, none of "
658 "which are slashes. Two processes can operate on the same named semaphore by "
659 "passing the same name to B<sem_open>(3)."
663 #: build/C/man7/sem_overview.7:79
665 "The B<sem_open>(3) function creates a new named semaphore or opens an "
666 "existing named semaphore. After the semaphore has been opened, it can be "
667 "operated on using B<sem_post>(3) and B<sem_wait>(3). When a process has "
668 "finished using the semaphore, it can use B<sem_close>(3) to close the "
669 "semaphore. When all processes have finished using the semaphore, it can be "
670 "removed from the system using B<sem_unlink>(3)."
674 #: build/C/man7/sem_overview.7:79
676 msgid "B<Unnamed semaphores (memory-based semaphores)>"
680 #: build/C/man7/sem_overview.7:94
682 "An unnamed semaphore does not have a name. Instead the semaphore is placed "
683 "in a region of memory that is shared between multiple threads (a "
684 "I<thread-shared semaphore>) or processes (a I<process-shared semaphore>). "
685 "A thread-shared semaphore is placed in an area of memory shared between the "
686 "threads of a process, for example, a global variable. A process-shared "
687 "semaphore must be placed in a shared memory region (e.g., a System V shared "
688 "memory segment created using B<shmget>(2), or a POSIX shared memory object "
689 "built created using B<shm_open>(3))."
693 #: build/C/man7/sem_overview.7:105
695 "Before being used, an unnamed semaphore must be initialized using "
696 "B<sem_init>(3). It can then be operated on using B<sem_post>(3) and "
697 "B<sem_wait>(3). When the semaphore is no longer required, and before the "
698 "memory in which it is located is deallocated, the semaphore should be "
699 "destroyed using B<sem_destroy>(3)."
703 #: build/C/man7/sem_overview.7:108
705 "The remainder of this section describes some specific details of the Linux "
706 "implementation of POSIX semaphores."
710 #: build/C/man7/sem_overview.7:108
716 #: build/C/man7/sem_overview.7:114
718 "Prior to kernel 2.6, Linux supported only unnamed, thread-shared "
719 "semaphores. On a system with Linux 2.6 and a glibc that provides the NPTL "
720 "threading implementation, a complete implementation of POSIX semaphores is "
725 #: build/C/man7/sem_overview.7:114
731 #: build/C/man7/sem_overview.7:119
733 "POSIX named semaphores have kernel persistence: if not removed by "
734 "B<sem_unlink>(3), a semaphore will exist until the system is shut down."
738 #: build/C/man7/sem_overview.7:119
744 #: build/C/man7/sem_overview.7:124
746 "Programs using the POSIX semaphores API must be compiled with I<cc -pthread> "
747 "to link against the real-time library, I<librt>."
751 #: build/C/man7/sem_overview.7:124
753 msgid "Accessing named semaphores via the filesystem"
757 #: build/C/man7/sem_overview.7:135
759 "On Linux, named semaphores are created in a virtual filesystem, normally "
760 "mounted under I</dev/shm>, with names of the form B<sem.>I<somename>. (This "
761 "is the reason that semaphore names are limited to B<NAME_MAX>I<-4> rather "
762 "than B<NAME_MAX> characters.)"
766 #: build/C/man7/sem_overview.7:138
768 "Since Linux 2.6.19, ACLs can be placed on files under this directory, to "
769 "control object permissions on a per-user and per-group basis."
773 #: build/C/man7/sem_overview.7:149
775 "System V semaphores (B<semget>(2), B<semop>(2), etc.) are an older semaphore "
776 "API. POSIX semaphores provide a simpler, and better designed interface than "
777 "System V semaphores; on the other hand POSIX semaphores are less widely "
778 "available (especially on older systems) than System V semaphores."
782 #: build/C/man7/sem_overview.7:149 build/C/man3/sem_post.3:72 build/C/man3/sem_wait.3:161 build/C/man2/semop.2:508
788 #: build/C/man7/sem_overview.7:152
790 "An example of the use of various POSIX semaphore functions is shown in "
795 #: build/C/man7/sem_overview.7:162
797 "B<sem_close>(3), B<sem_destroy>(3), B<sem_getvalue>(3), B<sem_init>(3), "
798 "B<sem_open>(3), B<sem_post>(3), B<sem_unlink>(3), B<sem_wait>(3), "
803 #: build/C/man3/sem_post.3:26
809 #: build/C/man3/sem_post.3:26 build/C/man3/sem_unlink.3:26 build/C/man3/sem_wait.3:26
815 #: build/C/man3/sem_post.3:29
816 msgid "sem_post - unlock a semaphore"
820 #: build/C/man3/sem_post.3:34
822 msgid "B<int sem_post(sem_t *>I<sem>B<);>\n"
826 #: build/C/man3/sem_post.3:45
828 "B<sem_post>() increments (unlocks) the semaphore pointed to by I<sem>. If "
829 "the semaphore's value consequently becomes greater than zero, then another "
830 "process or thread blocked in a B<sem_wait>(3) call will be woken up and "
831 "proceed to lock the semaphore."
835 #: build/C/man3/sem_post.3:52
837 "B<sem_post>() returns 0 on success; on error, the value of the semaphore is "
838 "left unchanged, -1 is returned, and I<errno> is set to indicate the error."
842 #: build/C/man3/sem_post.3:57
847 #. Added in POSIX.1-2008 TC1 (Austin Interpretation 213)
849 #: build/C/man3/sem_post.3:61
850 msgid "The maximum allowable value for a semaphore would be exceeded."
854 #: build/C/man3/sem_post.3:66
855 msgid "The B<sem_post>() function is thread-safe."
859 #: build/C/man3/sem_post.3:72
861 "B<sem_post>() is async-signal-safe: it may be safely called within a signal "
866 #: build/C/man3/sem_post.3:75
867 msgid "See B<sem_wait>(3)."
871 #: build/C/man3/sem_post.3:79
872 msgid "B<sem_getvalue>(3), B<sem_wait>(3), B<sem_overview>(7)"
876 #: build/C/man3/sem_unlink.3:26
882 #: build/C/man3/sem_unlink.3:29
883 msgid "sem_unlink - remove a named semaphore"
887 #: build/C/man3/sem_unlink.3:34
889 msgid "B<int sem_unlink(const char *>I<name>B<);>\n"
893 #: build/C/man3/sem_unlink.3:44
895 "B<sem_unlink>() removes the named semaphore referred to by I<name>. The "
896 "semaphore name is removed immediately. The semaphore is destroyed once all "
897 "other processes that have the semaphore open close it."
901 #: build/C/man3/sem_unlink.3:50
903 "On success B<sem_unlink>() returns 0; on error, -1 is returned, with "
904 "I<errno> set to indicate the error."
908 #: build/C/man3/sem_unlink.3:54
909 msgid "The caller does not have permission to unlink this semaphore."
913 #: build/C/man3/sem_unlink.3:62
914 msgid "There is no semaphore with the given I<name>."
918 #: build/C/man3/sem_unlink.3:67
919 msgid "The B<sem_unlink>() function is thread-safe."
923 #: build/C/man3/sem_unlink.3:75
925 "B<sem_getvalue>(3), B<sem_open>(3), B<sem_post>(3), B<sem_wait>(3), "
930 #: build/C/man3/sem_wait.3:26
936 #: build/C/man3/sem_wait.3:29
937 msgid "sem_wait, sem_timedwait, sem_trywait - lock a semaphore"
941 #: build/C/man3/sem_wait.3:34
943 msgid "B<int sem_wait(sem_t *>I<sem>B<);>\n"
947 #: build/C/man3/sem_wait.3:36
949 msgid "B<int sem_trywait(sem_t *>I<sem>B<);>\n"
953 #: build/C/man3/sem_wait.3:38
956 "B<int sem_timedwait(sem_t *>I<sem>B<, const struct timespec "
957 "*>I<abs_timeout>B<);>\n"
961 #: build/C/man3/sem_wait.3:45 build/C/man2/semop.2:53
962 msgid "Feature Test Macro Requirements for glibc (see B<feature_test_macros>(7)):"
966 #: build/C/man3/sem_wait.3:49
968 "B<sem_timedwait>(): _POSIX_C_SOURCE\\ E<gt>=\\ 200112L || _XOPEN_SOURCE\\ "
973 #: build/C/man3/sem_wait.3:59
975 "B<sem_wait>() decrements (locks) the semaphore pointed to by I<sem>. If "
976 "the semaphore's value is greater than zero, then the decrement proceeds, and "
977 "the function returns, immediately. If the semaphore currently has the value "
978 "zero, then the call blocks until either it becomes possible to perform the "
979 "decrement (i.e., the semaphore value rises above zero), or a signal handler "
980 "interrupts the call."
984 #: build/C/man3/sem_wait.3:69
986 "B<sem_trywait>() is the same as B<sem_wait>(), except that if the decrement "
987 "cannot be immediately performed, then call returns an error (I<errno> set to "
988 "B<EAGAIN>) instead of blocking."
992 #: build/C/man3/sem_wait.3:82
994 "B<sem_timedwait>() is the same as B<sem_wait>(), except that I<abs_timeout> "
995 "specifies a limit on the amount of time that the call should block if the "
996 "decrement cannot be immediately performed. The I<abs_timeout> argument "
997 "points to a structure that specifies an absolute timeout in seconds and "
998 "nanoseconds since the Epoch, 1970-01-01 00:00:00 +0000 (UTC). This "
999 "structure is defined as follows:"
1003 #: build/C/man3/sem_wait.3:89
1006 "struct timespec {\n"
1007 " time_t tv_sec; /* Seconds */\n"
1008 " long tv_nsec; /* Nanoseconds [0 .. 999999999] */\n"
1013 #: build/C/man3/sem_wait.3:100
1015 "If the timeout has already expired by the time of the call, and the "
1016 "semaphore could not be locked immediately, then B<sem_timedwait>() fails "
1017 "with a timeout error (I<errno> set to B<ETIMEDOUT>)."
1021 #: build/C/man3/sem_wait.3:108
1023 "If the operation can be performed immediately, then B<sem_timedwait>() "
1024 "never fails with a timeout error, regardless of the value of "
1025 "I<abs_timeout>. Furthermore, the validity of I<abs_timeout> is not checked "
1030 #: build/C/man3/sem_wait.3:114
1032 "All of these functions return 0 on success; on error, the value of the "
1033 "semaphore is left unchanged, -1 is returned, and I<errno> is set to indicate "
1038 #: build/C/man3/sem_wait.3:115 build/C/man2/semop.2:352
1044 #: build/C/man3/sem_wait.3:119
1045 msgid "The call was interrupted by a signal handler; see B<signal>(7)."
1049 #: build/C/man3/sem_wait.3:126
1050 msgid "The following additional error can occur for B<sem_trywait>():"
1054 #: build/C/man3/sem_wait.3:126 build/C/man2/semop.2:327
1060 #: build/C/man3/sem_wait.3:130
1062 "The operation could not be performed without blocking (i.e., the semaphore "
1063 "currently has the value zero)."
1067 #: build/C/man3/sem_wait.3:133
1068 msgid "The following additional errors can occur for B<sem_timedwait>():"
1072 #: build/C/man3/sem_wait.3:138
1074 "The value of I<abs_timeout.tv_nsecs> is less than 0, or greater than or "
1075 "equal to 1000 million."
1079 #: build/C/man3/sem_wait.3:138
1081 msgid "B<ETIMEDOUT>"
1084 #. POSIX.1-2001 also allows EDEADLK -- "A deadlock condition
1085 #. was detected", but this does not occur on Linux(?).
1087 #: build/C/man3/sem_wait.3:143
1088 msgid "The call timed out before the semaphore could be locked."
1092 #: build/C/man3/sem_wait.3:151
1094 "The B<sem_wait>(), B<sem_trywait>(), and B<sem_timedwait>() functions are "
1098 #. sem_wait() is always interrupted on most other implementations,
1099 #. but on FreeBSD 5.4 SA_RESTART does cause restarting.
1101 #: build/C/man3/sem_wait.3:161
1103 "A signal handler always interrupts a blocked call to one of these functions, "
1104 "regardless of the use of the B<sigaction>(2) B<SA_RESTART> flag."
1108 #: build/C/man3/sem_wait.3:180
1110 "The (somewhat trivial) program shown below operates on an unnamed "
1111 "semaphore. The program expects two command-line arguments. The first "
1112 "argument specifies a seconds value that is used to set an alarm timer to "
1113 "generate a B<SIGALRM> signal. This handler performs a B<sem_post>(3) to "
1114 "increment the semaphore that is being waited on in I<main()> using "
1115 "B<sem_timedwait>(). The second command-line argument specifies the length "
1116 "of the timeout, in seconds, for B<sem_timedwait>(). The following shows "
1117 "what happens on two different runs of the program:"
1121 #: build/C/man3/sem_wait.3:190
1124 "$B< ./a.out 2 3>\n"
1125 "About to call sem_timedwait()\n"
1126 "sem_post() from handler\n"
1127 "sem_timedwait() succeeded\n"
1128 "$B< ./a.out 2 1>\n"
1129 "About to call sem_timedwait()\n"
1130 "sem_timedwait() timed out\n"
1134 #: build/C/man3/sem_wait.3:192
1136 msgid "Program source"
1140 #: build/C/man3/sem_wait.3:203
1143 "#include E<lt>unistd.hE<gt>\n"
1144 "#include E<lt>stdio.hE<gt>\n"
1145 "#include E<lt>stdlib.hE<gt>\n"
1146 "#include E<lt>semaphore.hE<gt>\n"
1147 "#include E<lt>time.hE<gt>\n"
1148 "#include E<lt>assert.hE<gt>\n"
1149 "#include E<lt>errno.hE<gt>\n"
1150 "#include E<lt>signal.hE<gt>\n"
1154 #: build/C/man3/sem_wait.3:205
1156 msgid "sem_t sem;\n"
1160 #: build/C/man3/sem_wait.3:208
1163 "#define handle_error(msg) \\e\n"
1164 " do { perror(msg); exit(EXIT_FAILURE); } while (0)\n"
1168 #: build/C/man3/sem_wait.3:218
1172 "handler(int sig)\n"
1174 " write(STDOUT_FILENO, \"sem_post() from handler\\en\", 24);\n"
1175 " if (sem_post(&sem) == -1) {\n"
1176 " write(STDERR_FILENO, \"sem_post() failed\\en\", 18);\n"
1177 " _exit(EXIT_FAILURE);\n"
1183 #: build/C/man3/sem_wait.3:225
1187 "main(int argc, char *argv[])\n"
1189 " struct sigaction sa;\n"
1190 " struct timespec ts;\n"
1195 #: build/C/man3/sem_wait.3:231
1198 " if (argc != 3) {\n"
1199 " fprintf(stderr, \"Usage: %s E<lt>alarm-secsE<gt> "
1200 "E<lt>wait-secsE<gt>\\en\",\n"
1202 " exit(EXIT_FAILURE);\n"
1207 #: build/C/man3/sem_wait.3:234
1210 " if (sem_init(&sem, 0, 0) == -1)\n"
1211 " handle_error(\"sem_init\");\n"
1215 #: build/C/man3/sem_wait.3:236
1217 msgid " /* Establish SIGALRM handler; set alarm timer using argv[1] */\n"
1221 #: build/C/man3/sem_wait.3:242
1224 " sa.sa_handler = handler;\n"
1225 " sigemptyset(&sa.sa_mask);\n"
1226 " sa.sa_flags = 0;\n"
1227 " if (sigaction(SIGALRM, &sa, NULL) == -1)\n"
1228 " handle_error(\"sigaction\");\n"
1232 #: build/C/man3/sem_wait.3:244
1234 msgid " alarm(atoi(argv[1]));\n"
1238 #: build/C/man3/sem_wait.3:247
1241 " /* Calculate relative interval as current time plus\n"
1242 " number of seconds given argv[2] */\n"
1246 #: build/C/man3/sem_wait.3:250
1249 " if (clock_gettime(CLOCK_REALTIME, &ts) == -1)\n"
1250 " handle_error(\"clock_gettime\");\n"
1254 #: build/C/man3/sem_wait.3:252
1256 msgid " ts.tv_sec += atoi(argv[2]);\n"
1260 #: build/C/man3/sem_wait.3:256
1263 " printf(\"main() about to call sem_timedwait()\\en\");\n"
1264 " while ((s = sem_timedwait(&sem, &ts)) == -1 && errno == EINTR)\n"
1265 " continue; /* Restart if interrupted by handler */\n"
1269 #: build/C/man3/sem_wait.3:258
1271 msgid " /* Check what happened */\n"
1275 #: build/C/man3/sem_wait.3:266
1279 " if (errno == ETIMEDOUT)\n"
1280 " printf(\"sem_timedwait() timed out\\en\");\n"
1282 " perror(\"sem_timedwait\");\n"
1284 " printf(\"sem_timedwait() succeeded\\en\");\n"
1288 #: build/C/man3/sem_wait.3:269
1291 " exit((s == 0) ? EXIT_SUCCESS : EXIT_FAILURE);\n"
1296 #: build/C/man3/sem_wait.3:276
1298 "B<clock_gettime>(2), B<sem_getvalue>(3), B<sem_post>(3), B<sem_overview>(7), "
1303 #: build/C/man2/semctl.2:41
1309 #: build/C/man2/semctl.2:41
1315 #: build/C/man2/semctl.2:44
1316 msgid "semctl - System V semaphore control operations"
1320 #: build/C/man2/semctl.2:49 build/C/man2/semget.2:44 build/C/man2/semop.2:43
1323 "B<#include E<lt>sys/types.hE<gt>>\n"
1324 "B<#include E<lt>sys/ipc.hE<gt>>\n"
1325 "B<#include E<lt>sys/sem.hE<gt>>\n"
1329 #: build/C/man2/semctl.2:51
1331 msgid "B<int semctl(int >I<semid>B<, int >I<semnum>B<, int >I<cmd>B<, ...);>\n"
1335 #: build/C/man2/semctl.2:62
1337 "B<semctl>() performs the control operation specified by I<cmd> on the "
1338 "System\\ V semaphore set identified by I<semid>, or on the I<semnum>-th "
1339 "semaphore of that set. (The semaphores in a set are numbered starting at "
1344 #: build/C/man2/semctl.2:68
1346 "This function has three or four arguments, depending on I<cmd>. When there "
1347 "are four, the fourth has the type I<union semun>. The I<calling program> "
1348 "must define this union as follows:"
1352 #: build/C/man2/semctl.2:78
1356 " int val; /* Value for SETVAL */\n"
1357 " struct semid_ds *buf; /* Buffer for IPC_STAT, IPC_SET */\n"
1358 " unsigned short *array; /* Array for GETALL, SETALL */\n"
1359 " struct seminfo *__buf; /* Buffer for IPC_INFO\n"
1360 " (Linux-specific) */\n"
1365 #: build/C/man2/semctl.2:84
1367 "The I<semid_ds> data structure is defined in I<E<lt>sys/sem.hE<gt>> as "
1372 #: build/C/man2/semctl.2:93
1375 "struct semid_ds {\n"
1376 " struct ipc_perm sem_perm; /* Ownership and permissions */\n"
1377 " time_t sem_otime; /* Last semop time */\n"
1378 " time_t sem_ctime; /* Last change time */\n"
1379 " unsigned long sem_nsems; /* No. of semaphores in set */\n"
1384 #: build/C/man2/semctl.2:101
1386 "The I<ipc_perm> structure is defined as follows (the highlighted fields are "
1387 "settable using B<IPC_SET>):"
1391 #: build/C/man2/semctl.2:113
1394 "struct ipc_perm {\n"
1395 " key_t __key; /* Key supplied to semget(2) */\n"
1396 " uid_t B<uid>; /* Effective UID of owner */\n"
1397 " gid_t B<gid>; /* Effective GID of owner */\n"
1398 " uid_t cuid; /* Effective UID of creator */\n"
1399 " gid_t cgid; /* Effective GID of creator */\n"
1400 " unsigned short B<mode>; /* Permissions */\n"
1401 " unsigned short __seq; /* Sequence number */\n"
1406 #: build/C/man2/semctl.2:119
1407 msgid "Valid values for I<cmd> are:"
1411 #: build/C/man2/semctl.2:119
1417 #: build/C/man2/semctl.2:131
1419 "Copy information from the kernel data structure associated with I<semid> "
1420 "into the I<semid_ds> structure pointed to by I<arg.buf>. The argument "
1421 "I<semnum> is ignored. The calling process must have read permission on the "
1426 #: build/C/man2/semctl.2:131
1432 #: build/C/man2/semctl.2:154
1434 "Write the values of some members of the I<semid_ds> structure pointed to by "
1435 "I<arg.buf> to the kernel data structure associated with this semaphore set, "
1436 "updating also its I<sem_ctime> member. The following members of the "
1437 "structure are updated: I<sem_perm.uid>, I<sem_perm.gid>, and (the least "
1438 "significant 9 bits of) I<sem_perm.mode>. The effective UID of the calling "
1439 "process must match the owner (I<sem_perm.uid>) or creator "
1440 "(I<sem_perm.cuid>) of the semaphore set, or the caller must be privileged. "
1441 "The argument I<semnum> is ignored."
1445 #: build/C/man2/semctl.2:154
1451 #: build/C/man2/semctl.2:169
1453 "Immediately remove the semaphore set, awakening all processes blocked in "
1454 "B<semop>(2) calls on the set (with an error return and I<errno> set to "
1455 "B<EIDRM>). The effective user ID of the calling process must match the "
1456 "creator or owner of the semaphore set, or the caller must be privileged. "
1457 "The argument I<semnum> is ignored."
1461 #: build/C/man2/semctl.2:169
1463 msgid "B<IPC_INFO> (Linux-specific)"
1467 #: build/C/man2/semctl.2:181
1469 "Return information about system-wide semaphore limits and parameters in the "
1470 "structure pointed to by I<arg.__buf>. This structure is of type I<seminfo>, "
1471 "defined in I<E<lt>sys/sem.hE<gt>> if the B<_GNU_SOURCE> feature test macro "
1476 #: build/C/man2/semctl.2:203
1479 "struct seminfo {\n"
1480 " int semmap; /* Number of entries in semaphore\n"
1481 " map; unused within kernel */\n"
1482 " int semmni; /* Maximum number of semaphore sets */\n"
1483 " int semmns; /* Maximum number of semaphores in all\n"
1484 " semaphore sets */\n"
1485 " int semmnu; /* System-wide maximum number of undo\n"
1486 " structures; unused within kernel */\n"
1487 " int semmsl; /* Maximum number of semaphores in a\n"
1489 " int semopm; /* Maximum number of operations for\n"
1491 " int semume; /* Maximum number of undo entries per\n"
1492 " process; unused within kernel */\n"
1493 " int semusz; /* Size of struct sem_undo */\n"
1494 " int semvmx; /* Maximum semaphore value */\n"
1495 " int semaem; /* Max. value that can be recorded for\n"
1496 " semaphore adjustment (SEM_UNDO) */\n"
1501 #: build/C/man2/semctl.2:217
1503 "The I<semmsl>, I<semmns>, I<semopm>, and I<semmni> settings can be changed "
1504 "via I</proc/sys/kernel/sem>; see B<proc>(5) for details."
1508 #: build/C/man2/semctl.2:217
1510 msgid "B<SEM_INFO> (Linux-specific)"
1514 #: build/C/man2/semctl.2:231
1516 "Return a I<seminfo> structure containing the same information as for "
1517 "B<IPC_INFO>, except that the following fields are returned with information "
1518 "about system resources consumed by semaphores: the I<semusz> field returns "
1519 "the number of semaphore sets that currently exist on the system; and the "
1520 "I<semaem> field returns the total number of semaphores in all semaphore sets "
1525 #: build/C/man2/semctl.2:231
1527 msgid "B<SEM_STAT> (Linux-specific)"
1531 #: build/C/man2/semctl.2:242
1533 "Return a I<semid_ds> structure as for B<IPC_STAT>. However, the I<semid> "
1534 "argument is not a semaphore identifier, but instead an index into the "
1535 "kernel's internal array that maintains information about all semaphore sets "
1540 #: build/C/man2/semctl.2:242
1546 #: build/C/man2/semctl.2:253
1548 "Return B<semval> (i.e., the current value) for all semaphores of the set "
1549 "into I<arg.array>. The argument I<semnum> is ignored. The calling process "
1550 "must have read permission on the semaphore set."
1554 #: build/C/man2/semctl.2:253 build/C/man2/semctl.2:351
1560 #: build/C/man2/semctl.2:266
1562 "Return the value of B<semncnt> for the I<semnum>-th semaphore of the set "
1563 "(i.e., the number of processes waiting for an increase of B<semval> for the "
1564 "I<semnum>-th semaphore of the set). The calling process must have read "
1565 "permission on the semaphore set."
1569 #: build/C/man2/semctl.2:266 build/C/man2/semctl.2:355
1575 #: build/C/man2/semctl.2:279
1577 "Return the value of B<sempid> for the I<semnum>-th semaphore of the set "
1578 "(i.e., the PID of the process that executed the last B<semop>(2) call for "
1579 "the I<semnum>-th semaphore of the set). The calling process must have read "
1580 "permission on the semaphore set."
1584 #: build/C/man2/semctl.2:279 build/C/man2/semctl.2:359
1590 #: build/C/man2/semctl.2:287
1592 "Return the value of B<semval> for the I<semnum>-th semaphore of the set. "
1593 "The calling process must have read permission on the semaphore set."
1597 #: build/C/man2/semctl.2:287 build/C/man2/semctl.2:363
1603 #: build/C/man2/semctl.2:300
1605 "Return the value of B<semzcnt> for the I<semnum>-th semaphore of the set "
1606 "(i.e., the number of processes waiting for B<semval> of the I<semnum>-th "
1607 "semaphore of the set to become 0). The calling process must have read "
1608 "permission on the semaphore set."
1612 #: build/C/man2/semctl.2:300
1618 #: build/C/man2/semctl.2:322
1620 "Set B<semval> for all semaphores of the set using I<arg.array>, updating "
1621 "also the I<sem_ctime> member of the I<semid_ds> structure associated with "
1622 "the set. Undo entries (see B<semop>(2)) are cleared for altered semaphores "
1623 "in all processes. If the changes to semaphore values would permit blocked "
1624 "B<semop>(2) calls in other processes to proceed, then those processes are "
1625 "woken up. The argument I<semnum> is ignored. The calling process must have "
1626 "alter (write) permission on the semaphore set."
1630 #: build/C/man2/semctl.2:322
1636 #: build/C/man2/semctl.2:340
1638 "Set the value of B<semval> to I<arg.val> for the I<semnum>-th semaphore of "
1639 "the set, updating also the I<sem_ctime> member of the I<semid_ds> structure "
1640 "associated with the set. Undo entries are cleared for altered semaphores in "
1641 "all processes. If the changes to semaphore values would permit blocked "
1642 "B<semop>(2) calls in other processes to proceed, then those processes are "
1643 "woken up. The calling process must have alter permission on the semaphore "
1648 #: build/C/man2/semctl.2:347
1649 msgid "On failure, B<semctl>() returns -1 with I<errno> indicating the error."
1653 #: build/C/man2/semctl.2:351
1655 "Otherwise, the system call returns a nonnegative value depending on I<cmd> "
1660 #: build/C/man2/semctl.2:355
1661 msgid "the value of B<semncnt>."
1665 #: build/C/man2/semctl.2:359
1666 msgid "the value of B<sempid>."
1670 #: build/C/man2/semctl.2:363
1671 msgid "the value of B<semval>."
1675 #: build/C/man2/semctl.2:367
1676 msgid "the value of B<semzcnt>."
1680 #: build/C/man2/semctl.2:367
1686 #: build/C/man2/semctl.2:375
1688 "the index of the highest used entry in the kernel's internal array recording "
1689 "information about all semaphore sets. (This information can be used with "
1690 "repeated B<SEM_STAT> operations to obtain information about all semaphore "
1691 "sets on the system.)"
1695 #: build/C/man2/semctl.2:375
1701 #: build/C/man2/semctl.2:379
1702 msgid "as for B<IPC_INFO>."
1706 #: build/C/man2/semctl.2:379
1712 #: build/C/man2/semctl.2:383
1713 msgid "the identifier of the semaphore set whose index was given in I<semid>."
1717 #: build/C/man2/semctl.2:387
1718 msgid "All other I<cmd> values return 0 on success."
1722 #: build/C/man2/semctl.2:391 build/C/man2/semget.2:157
1723 msgid "On failure, I<errno> will be set to one of the following:"
1727 #: build/C/man2/semctl.2:410
1729 "The argument I<cmd> has one of the values B<GETALL>, B<GETPID>, B<GETVAL>, "
1730 "B<GETNCNT>, B<GETZCNT>, B<IPC_STAT>, B<SEM_STAT>, B<SETALL>, or B<SETVAL> "
1731 "and the calling process does not have the required permissions on the "
1732 "semaphore set and does not have the B<CAP_IPC_OWNER> capability."
1736 #: build/C/man2/semctl.2:410 build/C/man2/semop.2:336
1742 #: build/C/man2/semctl.2:417
1743 msgid "The address pointed to by I<arg.buf> or I<arg.array> isn't accessible."
1747 #: build/C/man2/semctl.2:417 build/C/man2/semop.2:349
1753 #: build/C/man2/semctl.2:420 build/C/man2/semop.2:352
1754 msgid "The semaphore set was removed."
1758 #: build/C/man2/semctl.2:431
1760 "Invalid value for I<cmd> or I<semid>. Or: for a B<SEM_STAT> operation, the "
1761 "index value specified in I<semid> referred to an array slot that is "
1766 #: build/C/man2/semctl.2:431
1772 #: build/C/man2/semctl.2:449
1774 "The argument I<cmd> has the value B<IPC_SET> or B<IPC_RMID> but the "
1775 "effective user ID of the calling process is not the creator (as found in "
1776 "I<sem_perm.cuid>) or the owner (as found in I<sem_perm.uid>) of the "
1777 "semaphore set, and the process does not have the B<CAP_SYS_ADMIN> "
1782 #: build/C/man2/semctl.2:449 build/C/man2/semop.2:371
1788 #: build/C/man2/semctl.2:462
1790 "The argument I<cmd> has the value B<SETALL> or B<SETVAL> and the value to "
1791 "which B<semval> is to be set (for some semaphore of the set) is less than 0 "
1792 "or greater than the implementation limit B<SEMVMX>."
1795 #. SVr4 documents additional error conditions EINVAL, EFBIG, ENOSPC.
1797 #: build/C/man2/semctl.2:465 build/C/man2/semget.2:214 build/C/man2/semop.2:389
1798 msgid "SVr4, POSIX.1-2001."
1802 #: build/C/man2/semctl.2:476
1804 "POSIX.1-2001 specifies the I<sem_nsems> field of the I<semid_ds> structure "
1805 "as having the type I<unsigned\\ short>, and the field is so defined on most "
1806 "other systems. It was also so defined on Linux 2.2 and earlier, but, since "
1807 "Linux 2.4, the field has the type I<unsigned\\ long>."
1810 #. Like Linux, the FreeBSD man pages still document
1811 #. the inclusion of these header files.
1813 #: build/C/man2/semctl.2:489 build/C/man2/semget.2:227 build/C/man2/semop.2:402
1815 "The inclusion of I<E<lt>sys/types.hE<gt>> and I<E<lt>sys/ipc.hE<gt>> isn't "
1816 "required on Linux or by any version of POSIX. However, some old "
1817 "implementations required the inclusion of these header files, and the SVID "
1818 "also documented their inclusion. Applications intended to be portable to "
1819 "such old systems may need to include these header files."
1823 #: build/C/man2/semctl.2:501
1825 "The B<IPC_INFO>, B<SEM_STAT> and B<SEM_INFO> operations are used by the "
1826 "B<ipcs>(1) program to provide information on allocated resources. In the "
1827 "future these may modified or moved to a I</proc> filesystem interface."
1831 #: build/C/man2/semctl.2:514
1833 "Various fields in a I<struct semid_ds> were typed as I<short> under Linux "
1834 "2.2 and have become I<long> under Linux 2.4. To take advantage of this, a "
1835 "recompilation under glibc-2.1.91 or later should suffice. (The kernel "
1836 "distinguishes old and new calls by an B<IPC_64> flag in I<cmd>.)"
1840 #: build/C/man2/semctl.2:523
1842 "In some earlier versions of glibc, the I<semun> union was defined in "
1843 "I<E<lt>sys/sem.hE<gt>>, but POSIX.1-2001 requires that the caller define "
1844 "this union. On versions of glibc where this union is I<not> defined, the "
1845 "macro B<_SEM_SEMUN_UNDEFINED> is defined in I<E<lt>sys/sem.hE<gt>>."
1849 #: build/C/man2/semctl.2:527
1850 msgid "The following system limit on semaphore sets affects a B<semctl>() call:"
1854 #: build/C/man2/semctl.2:527 build/C/man2/semop.2:466
1860 #: build/C/man2/semctl.2:532
1861 msgid "Maximum value for B<semval>: implementation dependent (32767)."
1865 #: build/C/man2/semctl.2:536
1867 "For greater portability, it is best to always call B<semctl>() with four "
1872 #: build/C/man2/semctl.2:543
1874 "B<ipc>(2), B<semget>(2), B<semop>(2), B<capabilities>(7), "
1875 "B<sem_overview>(7), B<svipc>(7)"
1879 #: build/C/man2/semget.2:36
1885 #: build/C/man2/semget.2:36
1891 #: build/C/man2/semget.2:39
1892 msgid "semget - get a System V semaphore set identifier"
1896 #: build/C/man2/semget.2:49
1897 msgid "B<int semget(key_t >I<key>B<,> B<int >I<nsems>B<,> B<int >I<semflg>B<);>"
1901 #: build/C/man2/semget.2:67
1903 "The B<semget>() system call returns the System\\ V semaphore set identifier "
1904 "associated with the argument I<key>. A new set of I<nsems> semaphores is "
1905 "created if I<key> has the value B<IPC_PRIVATE> or if no existing semaphore "
1906 "set is associated with I<key> and B<IPC_CREAT> is specified in I<semflg>."
1910 #: build/C/man2/semget.2:86
1912 "If I<semflg> specifies both B<IPC_CREAT> and B<IPC_EXCL> and a semaphore set "
1913 "already exists for I<key>, then B<semget>() fails with I<errno> set to "
1914 "B<EEXIST>. (This is analogous to the effect of the combination B<O_CREAT | "
1915 "O_EXCL> for B<open>(2).)"
1919 #: build/C/man2/semget.2:99
1921 "Upon creation, the least significant 9 bits of the argument I<semflg> define "
1922 "the permissions (for owner, group and others) for the semaphore set. These "
1923 "bits have the same format, and the same meaning, as the I<mode> argument of "
1924 "B<open>(2) (though the execute permissions are not meaningful for "
1925 "semaphores, and write permissions mean permission to alter semaphore "
1930 #: build/C/man2/semget.2:107
1932 "When creating a new semaphore set, B<semget>() initializes the set's "
1933 "associated data structure, I<semid_ds> (see B<semctl>(2)), as follows:"
1937 #: build/C/man2/semget.2:112
1939 "I<sem_perm.cuid> and I<sem_perm.uid> are set to the effective user ID of the "
1944 #: build/C/man2/semget.2:117
1946 "I<sem_perm.cgid> and I<sem_perm.gid> are set to the effective group ID of "
1947 "the calling process."
1951 #: build/C/man2/semget.2:122
1953 "The least significant 9 bits of I<sem_perm.mode> are set to the least "
1954 "significant 9 bits of I<semflg>."
1958 #: build/C/man2/semget.2:126
1959 msgid "I<sem_nsems> is set to the value of I<nsems>."
1963 #: build/C/man2/semget.2:129
1964 msgid "I<sem_otime> is set to 0."
1968 #: build/C/man2/semget.2:132
1969 msgid "I<sem_ctime> is set to the current time."
1973 #: build/C/man2/semget.2:143
1975 "The argument I<nsems> can be 0 (a don't care) when a semaphore set is not "
1976 "being created. Otherwise, I<nsems> must be greater than 0 and less than or "
1977 "equal to the maximum number of semaphores per semaphore set (B<SEMMSL>)."
1980 #. and a check is made to see if it is marked for destruction.
1982 #: build/C/man2/semget.2:147
1983 msgid "If the semaphore set already exists, the permissions are verified."
1987 #: build/C/man2/semget.2:153
1989 "If successful, the return value will be the semaphore set identifier (a "
1990 "nonnegative integer), otherwise, -1 is returned, with I<errno> indicating "
1995 #: build/C/man2/semget.2:165
1997 "A semaphore set exists for I<key>, but the calling process does not have "
1998 "permission to access the set, and does not have the B<CAP_IPC_OWNER> "
2004 #. The semaphore set is marked to be deleted.
2006 #: build/C/man2/semget.2:177
2008 "B<IPC_CREAT> and B<IPC_EXCL> were specified in I<semflg>, but a semaphore "
2009 "set already exists for I<key>."
2013 #: build/C/man2/semget.2:183
2015 "I<nsems> is less than 0 or greater than the limit on the number of "
2016 "semaphores per semaphore set (B<SEMMSL>)."
2020 #: build/C/man2/semget.2:190
2022 "A semaphore set corresponding to I<key> already exists, but I<nsems> is "
2023 "larger than the number of semaphores in that set."
2027 #: build/C/man2/semget.2:198
2029 "No semaphore set exists for I<key> and I<semflg> did not specify "
2034 #: build/C/man2/semget.2:202
2036 "A semaphore set has to be created but the system does not have enough memory "
2037 "for the new data structure."
2041 #: build/C/man2/semget.2:202
2047 #: build/C/man2/semget.2:210
2049 "A semaphore set has to be created but the system limit for the maximum "
2050 "number of semaphore sets (B<SEMMNI>), or the system wide maximum number of "
2051 "semaphores (B<SEMMNS>), would be exceeded."
2055 #: build/C/man2/semget.2:238
2057 "B<IPC_PRIVATE> isn't a flag field but a I<key_t> type. If this special "
2058 "value is used for I<key>, the system call ignores all but the least "
2059 "significant 9 bits of I<semflg> and creates a new semaphore set (on "
2064 #: build/C/man2/semget.2:238
2066 msgid "Semaphore initialization"
2069 #. In truth, every one of the many implementations that I've tested sets
2070 #. the values to zero, but I suppose there is/was some obscure
2071 #. implementation out there that does not.
2073 #: build/C/man2/semget.2:250
2075 "The values of the semaphores in a newly created set are indeterminate. "
2076 "(POSIX.1-2001 and POSIX.1-2008 are explicit on this point, although "
2077 "POSIX.1-2008 notes that a future version of the standard may require an "
2078 "implementation to initialize the semaphores to 0.) Although Linux, like "
2079 "many other implementations, initializes the semaphore values to 0, a "
2080 "portable application cannot rely on this: it should explicitly initialize "
2081 "the semaphores to the desired values."
2085 #: build/C/man2/semget.2:265
2087 "Initialization can be done using B<semctl>(2) B<SETVAL> or B<SETALL> "
2088 "operation. Where multiple peers do not know who will be the first to "
2089 "initialize the set, checking for a nonzero I<sem_otime> in the associated "
2090 "data structure retrieved by a B<semctl>(2) B<IPC_STAT> operation can be "
2091 "used to avoid races."
2095 #: build/C/man2/semget.2:265 build/C/man2/semop.2:454
2097 msgid "Semaphore limits"
2101 #: build/C/man2/semget.2:269
2103 "The following limits on semaphore set resources affect the B<semget>() "
2108 #: build/C/man2/semget.2:269
2113 #. This /proc file is not available in Linux 2.2 and earlier -- MTK
2115 #: build/C/man2/semget.2:275
2117 "System-wide limit on the number of semaphore sets: policy dependent (on "
2118 "Linux, this limit can be read and modified via the fourth field of "
2119 "I</proc/sys/kernel/sem>)."
2123 #: build/C/man2/semget.2:275
2129 #: build/C/man2/semget.2:280
2131 "Maximum number of semaphores per semaphore ID: implementation dependent (on "
2132 "Linux, this limit can be read and modified via the first field of "
2133 "I</proc/sys/kernel/sem>)."
2137 #: build/C/man2/semget.2:280
2143 #: build/C/man2/semget.2:290
2145 "System-wide limit on the number of semaphores: policy dependent (on Linux, "
2146 "this limit can be read and modified via the second field of "
2147 "I</proc/sys/kernel/sem>). Note that the number of semaphores system-wide is "
2148 "also limited by the product of B<SEMMSL> and B<SEMMNI>."
2152 #: build/C/man2/semget.2:290 build/C/man2/semop.2:478
2158 #: build/C/man2/semget.2:296
2160 "The name choice B<IPC_PRIVATE> was perhaps unfortunate, B<IPC_NEW> would "
2161 "more clearly show its function."
2165 #: build/C/man2/semget.2:303
2167 "B<semctl>(2), B<semop>(2), B<ftok>(3), B<capabilities>(7), "
2168 "B<sem_overview>(7), B<svipc>(7)"
2172 #: build/C/man2/semop.2:35
2178 #: build/C/man2/semop.2:35
2184 #: build/C/man2/semop.2:38
2185 msgid "semop, semtimedop - System V semaphore operations"
2189 #: build/C/man2/semop.2:45
2192 "B<int semop(int >I<semid>B<, struct sembuf *>I<sops>B<, size_t "
2197 #: build/C/man2/semop.2:48
2200 "B<int semtimedop(int >I<semid>B<, struct sembuf *>I<sops>B<, size_t "
2202 "B< const struct timespec *>I<timeout>B<);>\n"
2206 #: build/C/man2/semop.2:57
2207 msgid "B<semtimedop>(): _GNU_SOURCE"
2211 #: build/C/man2/semop.2:60
2213 "Each semaphore in a System\\ V semaphore set has the following associated "
2218 #: build/C/man2/semop.2:67
2221 "unsigned short semval; /* semaphore value */\n"
2222 "unsigned short semzcnt; /* # waiting for zero */\n"
2223 "unsigned short semncnt; /* # waiting for increase */\n"
2224 "pid_t sempid; /* ID of process that did last op */\n"
2228 #: build/C/man2/semop.2:82
2230 "B<semop>() performs operations on selected semaphores in the set indicated "
2231 "by I<semid>. Each of the I<nsops> elements in the array pointed to by "
2232 "I<sops> is a structure that specifies an operation to be performed on a "
2233 "single semaphore. The elements of this structure are of type I<struct "
2234 "sembuf>, containing the following members:"
2238 #: build/C/man2/semop.2:88
2241 "unsigned short sem_num; /* semaphore number */\n"
2242 "short sem_op; /* semaphore operation */\n"
2243 "short sem_flg; /* operation flags */\n"
2247 #: build/C/man2/semop.2:100
2249 "Flags recognized in I<sem_flg> are B<IPC_NOWAIT> and B<SEM_UNDO>. If an "
2250 "operation specifies B<SEM_UNDO>, it will be automatically undone when the "
2251 "process terminates."
2255 #: build/C/man2/semop.2:115
2257 "The set of operations contained in I<sops> is performed in I<array order>, "
2258 "and I<atomically>, that is, the operations are performed either as a "
2259 "complete unit, or not at all. The behavior of the system call if not all "
2260 "operations can be performed immediately depends on the presence of the "
2261 "B<IPC_NOWAIT> flag in the individual I<sem_flg> fields, as noted below."
2265 #: build/C/man2/semop.2:122
2267 "Each operation is performed on the I<sem_num>-th semaphore of the semaphore "
2268 "set, where the first semaphore of the set is numbered 0. There are three "
2269 "types of operation, distinguished by the value of I<sem_op>."
2273 #: build/C/man2/semop.2:137
2275 "If I<sem_op> is a positive integer, the operation adds this value to the "
2276 "semaphore value (I<semval>). Furthermore, if B<SEM_UNDO> is specified for "
2277 "this operation, the system subtracts the value I<sem_op> from the semaphore "
2278 "adjustment (I<semadj>) value for this semaphore. This operation can always "
2279 "proceed\\(emit never forces a thread to wait. The calling process must have "
2280 "alter permission on the semaphore set."
2284 #: build/C/man2/semop.2:162
2286 "If I<sem_op> is zero, the process must have read permission on the semaphore "
2287 "set. This is a \"wait-for-zero\" operation: if I<semval> is zero, the "
2288 "operation can immediately proceed. Otherwise, if B<IPC_NOWAIT> is specified "
2289 "in I<sem_flg>, B<semop>() fails with I<errno> set to B<EAGAIN> (and none of "
2290 "the operations in I<sops> is performed). Otherwise, I<semzcnt> (the count "
2291 "of threads waiting until this semaphore's value becomes zero) is "
2292 "incremented by one and the thread sleeps until one of the following occurs:"
2296 #: build/C/man2/semop.2:162 build/C/man2/semop.2:167 build/C/man2/semop.2:175 build/C/man2/semop.2:227 build/C/man2/semop.2:232 build/C/man2/semop.2:239
2302 #: build/C/man2/semop.2:167
2303 msgid "I<semval> becomes 0, at which time the value of I<semzcnt> is decremented."
2307 #: build/C/man2/semop.2:175
2309 "The semaphore set is removed: B<semop>() fails, with I<errno> set to "
2314 #: build/C/man2/semop.2:185
2316 "The calling thread catches a signal: the value of I<semzcnt> is decremented "
2317 "and B<semop>() fails, with I<errno> set to B<EINTR>."
2321 #: build/C/man2/semop.2:227
2323 "If I<sem_op> is less than zero, the process must have alter permission on "
2324 "the semaphore set. If I<semval> is greater than or equal to the absolute "
2325 "value of I<sem_op>, the operation can proceed immediately: the absolute "
2326 "value of I<sem_op> is subtracted from I<semval>, and, if B<SEM_UNDO> is "
2327 "specified for this operation, the system adds the absolute value of "
2328 "I<sem_op> to the semaphore adjustment (I<semadj>) value for this "
2329 "semaphore. If the absolute value of I<sem_op> is greater than I<semval>, "
2330 "and B<IPC_NOWAIT> is specified in I<sem_flg>, B<semop>() fails, with "
2331 "I<errno> set to B<EAGAIN> (and none of the operations in I<sops> is "
2332 "performed). Otherwise, I<semncnt> (the counter of threads waiting for this "
2333 "semaphore's value to increase) is incremented by one and the thread sleeps "
2334 "until one of the following occurs:"
2338 #: build/C/man2/semop.2:232
2340 "I<semval> becomes greater than or equal to the absolute value of I<sem_op>: "
2341 "the operation now proceeds, as described above."
2345 #: build/C/man2/semop.2:239
2347 "The semaphore set is removed from the system: B<semop>() fails, with "
2348 "I<errno> set to B<EIDRM>."
2352 #: build/C/man2/semop.2:249
2354 "The calling thread catches a signal: the value of I<semncnt> is decremented "
2355 "and B<semop>() fails, with I<errno> set to B<EINTR>."
2361 #: build/C/man2/semop.2:260
2363 "On successful completion, the I<sempid> value for each semaphore specified "
2364 "in the array pointed to by I<sops> is set to the caller's process ID. In "
2365 "addition, the I<sem_otime> is set to the current time."
2369 #: build/C/man2/semop.2:260
2371 msgid "semtimedop()"
2375 #: build/C/man2/semop.2:290
2377 "B<semtimedop>() behaves identically to B<semop>() except that in those "
2378 "cases where the calling thread would sleep, the duration of that sleep is "
2379 "limited by the amount of elapsed time specified by the I<timespec> structure "
2380 "whose address is passed in the I<timeout> argument. (This sleep interval "
2381 "will be rounded up to the system clock granularity, and kernel scheduling "
2382 "delays mean that the interval may overrun by a small amount.) If the "
2383 "specified time limit has been reached, B<semtimedop>() fails with I<errno> "
2384 "set to B<EAGAIN> (and none of the operations in I<sops> is performed). If "
2385 "the I<timeout> argument is NULL, then B<semtimedop>() behaves exactly like "
2390 #: build/C/man2/semop.2:298
2392 "Note that if B<semtimeop>() is interrupted by a signal, causing the call to "
2393 "fail with the error B<EINTR>, the contents of I<timeout> are left unchanged."
2397 #: build/C/man2/semop.2:308
2399 "If successful, B<semop>() and B<semtimedop>() return 0; otherwise they "
2400 "return -1 with I<errno> indicating the error."
2404 #: build/C/man2/semop.2:312
2405 msgid "On failure, I<errno> is set to one of the following:"
2409 #: build/C/man2/semop.2:312
2415 #: build/C/man2/semop.2:320
2417 "The argument I<nsops> is greater than B<SEMOPM>, the maximum number of "
2418 "operations allowed per system call."
2422 #: build/C/man2/semop.2:327
2424 "The calling process does not have the permissions required to perform the "
2425 "specified semaphore operations, and does not have the B<CAP_IPC_OWNER> "
2430 #: build/C/man2/semop.2:336
2432 "An operation could not proceed immediately and either B<IPC_NOWAIT> was "
2433 "specified in I<sem_flg> or the time limit specified in I<timeout> expired."
2437 #: build/C/man2/semop.2:343
2439 "An address specified in either the I<sops> or the I<timeout> argument isn't "
2444 #: build/C/man2/semop.2:343
2450 #: build/C/man2/semop.2:349
2452 "For some operation the value of I<sem_num> is less than 0 or greater than or "
2453 "equal to the number of semaphores in the set."
2457 #: build/C/man2/semop.2:356
2459 "While blocked in this system call, the thread caught a signal; see "
2464 #: build/C/man2/semop.2:363
2466 "The semaphore set doesn't exist, or I<semid> is less than zero, or I<nsops> "
2467 "has a nonpositive value."
2471 #: build/C/man2/semop.2:371
2473 "The I<sem_flg> of some operation specified B<SEM_UNDO> and the system does "
2474 "not have enough memory to allocate the undo structure."
2478 #: build/C/man2/semop.2:379
2480 "For some operation I<sem_op+semval> is greater than B<SEMVMX>, the "
2481 "implementation dependent maximum value for I<semval>."
2485 #: build/C/man2/semop.2:379
2491 #: build/C/man2/semop.2:386
2493 "B<semtimedop>() first appeared in Linux 2.5.52, and was subsequently "
2494 "backported into kernel 2.4.22. Glibc support for B<semtimedop>() first "
2495 "appeared in version 2.3.3."
2499 #: build/C/man2/semop.2:410
2501 "The I<sem_undo> structures of a process aren't inherited by the child "
2502 "produced by B<fork>(2), but they are inherited across an B<execve>(2) "
2507 #: build/C/man2/semop.2:416
2509 "B<semop>() is never automatically restarted after being interrupted by a "
2510 "signal handler, regardless of the setting of the B<SA_RESTART> flag when "
2511 "establishing a signal handler."
2515 #: build/C/man2/semop.2:449
2517 "A semaphore adjustment (I<semadj>) value is a per-process, per-semaphore "
2518 "integer that is the negated sum of all operations performed on a semaphore "
2519 "specifying the B<SEM_UNDO> flag. Each process has a list of I<semadj> "
2520 "values\\(emone value for each semaphore on which it has operated using "
2521 "B<SEM_UNDO>. When a process terminates, each of its per-semaphore I<semadj> "
2522 "values is added to the corresponding semaphore, thus undoing the effect of "
2523 "that process's operations on the semaphore (but see BUGS below). When a "
2524 "semaphore's value is directly set using the B<SETVAL> or B<SETALL> request "
2525 "to B<semctl>(2), the corresponding I<semadj> values in all processes are "
2526 "cleared. The B<clone>(2) B<CLONE_SYSVSEM> flag allows more than one "
2527 "process to share a I<semadj> list; see B<clone>(2) for details."
2531 #: build/C/man2/semop.2:454
2533 "The I<semval>, I<sempid>, I<semzcnt>, and I<semnct> values for a semaphore "
2534 "can all be retrieved using appropriate B<semctl>(2) calls."
2538 #: build/C/man2/semop.2:458
2539 msgid "The following limits on semaphore set resources affect the B<semop>() call:"
2543 #: build/C/man2/semop.2:458
2548 #. This /proc file is not available in Linux 2.2 and earlier -- MTK
2550 #: build/C/man2/semop.2:466
2552 "Maximum number of operations allowed for one B<semop>() call (32) (on "
2553 "Linux, this limit can be read and modified via the third field of "
2554 "I</proc/sys/kernel/sem>)."
2558 #: build/C/man2/semop.2:471
2559 msgid "Maximum allowable value for I<semval>: implementation dependent (32767)."
2563 #: build/C/man2/semop.2:478
2565 "The implementation has no intrinsic limits for the adjust on exit maximum "
2566 "value (B<SEMAEM>), the system wide maximum number of undo structures "
2567 "(B<SEMMNU>) and the per-process maximum number of undo entries system "
2572 #: build/C/man2/semop.2:499
2574 "When a process terminates, its set of associated I<semadj> structures is "
2575 "used to undo the effect of all of the semaphore operations it performed with "
2576 "the B<SEM_UNDO> flag. This raises a difficulty: if one (or more) of these "
2577 "semaphore adjustments would result in an attempt to decrease a semaphore's "
2578 "value below zero, what should an implementation do? One possible approach "
2579 "would be to block until all the semaphore adjustments could be performed. "
2580 "This is however undesirable since it could force process termination to "
2581 "block for arbitrarily long periods. Another possibility is that such "
2582 "semaphore adjustments could be ignored altogether (somewhat analogously to "
2583 "failing when B<IPC_NOWAIT> is specified for a semaphore operation). Linux "
2584 "adopts a third approach: decreasing the semaphore value as far as possible "
2585 "(i.e., to zero) and allowing process termination to proceed immediately."
2589 #. http://marc.theaimsgroup.com/?l=linux-kernel&m=110260821123863&w=2
2591 #. http://marc.theaimsgroup.com/?l=linux-kernel&m=110261701025794&w=2
2593 #: build/C/man2/semop.2:508
2595 "In kernels 2.6.x, x E<lt>= 10, there is a bug that in some circumstances "
2596 "prevents a thread that is waiting for a semaphore value to become zero from "
2597 "being woken up when the value does actually become zero. This bug is fixed "
2602 #: build/C/man2/semop.2:513
2604 "The following code segment uses B<semop>() to atomically wait for the value "
2605 "of semaphore 0 to become zero, and then increment the semaphore value by "
2610 #: build/C/man2/semop.2:517
2613 " struct sembuf sops[2];\n"
2618 #: build/C/man2/semop.2:519
2620 msgid " /* Code to set I<semid> omitted */\n"
2624 #: build/C/man2/semop.2:523
2627 " sops[0].sem_num = 0; /* Operate on semaphore 0 */\n"
2628 " sops[0].sem_op = 0; /* Wait for value to equal 0 */\n"
2629 " sops[0].sem_flg = 0;\n"
2633 #: build/C/man2/semop.2:527
2636 " sops[1].sem_num = 0; /* Operate on semaphore 0 */\n"
2637 " sops[1].sem_op = 1; /* Increment value by one */\n"
2638 " sops[1].sem_flg = 0;\n"
2642 #: build/C/man2/semop.2:532
2645 " if (semop(semid, sops, 2) == -1) {\n"
2646 " perror(\"semop\");\n"
2647 " exit(EXIT_FAILURE);\n"
2652 #: build/C/man2/semop.2:542
2654 "B<clone>(2), B<semctl>(2), B<semget>(2), B<sigaction>(2), "
2655 "B<capabilities>(7), B<sem_overview>(7), B<svipc>(7), B<time>(7)"