1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
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23 .TH FLOCKFILE 3 2008-08-29 "" "Linux Programmer's Manual"
25 flockfile, ftrylockfile, funlockfile \- lock FILE for stdio
30 .BI "void flockfile(FILE *" filehandle );
32 .BI "int ftrylockfile(FILE *" filehandle );
34 .BI "void funlockfile(FILE *" filehandle );
38 Feature Test Macro Requirements for glibc (see
39 .BR feature_test_macros (7)):
43 All functions shown above:
45 _POSIX_C_SOURCE\ >=\ 1 || _XOPEN_SOURCE || _BSD_SOURCE ||
46 _SVID_SOURCE || _POSIX_SOURCE
50 The stdio functions are thread-safe.
51 This is achieved by assigning
54 object a lockcount and (if the lockcount is nonzero)
56 For each library call, these functions wait until the
59 is no longer locked by a different thread, then lock it, do the
60 requested I/O, and unlock the object again.
62 (Note: this locking has nothing to do with the file locking done
68 All this is invisible to the C-programmer, but there may be two
69 reasons to wish for more detailed control.
70 On the one hand, maybe
71 a series of I/O actions by one thread belongs together, and should
72 not be interrupted by the I/O of some other thread.
73 On the other hand, maybe the locking overhead should be avoided
74 for greater efficiency.
76 To this end, a thread can explicitly lock the
79 then do its series of I/O actions, then unlock.
81 other threads from coming in between.
82 If the reason for doing
83 this was to achieve greater efficiency, one does the I/O with
84 the nonlocking versions of the stdio functions: with
95 function waits for \fI*filehandle\fP to be
96 no longer locked by a different thread, then makes the
97 current thread owner of \fI*filehandle\fP, and increments
102 function decrements the lock count.
106 function is a nonblocking version
109 It does nothing in case some other thread
110 owns \fI*filehandle\fP, and it obtains ownership and increments
111 the lockcount otherwise.
115 function returns zero for success
116 (the lock was obtained), and nonzero for failure.
122 These functions are available when
123 .B _POSIX_THREAD_SAFE_FUNCTIONS
125 They are in libc since libc 5.1.1 and in glibc
128 .BR unlocked_stdio (3)