1 .\" Copyright (C) 2003 Davide Libenzi
2 .\" Davide Libenzi <davidel@xmailserver.org>
4 .\" %%%LICENSE_START(GPLv2+_SW_3_PARA)
5 .\" This program is free software; you can redistribute it and/or modify
6 .\" it under the terms of the GNU General Public License as published by
7 .\" the Free Software Foundation; either version 2 of the License, or
8 .\" (at your option) any later version.
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11 .\" but WITHOUT ANY WARRANTY; without even the implied warranty of
12 .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 .\" GNU General Public License for more details.
15 .\" You should have received a copy of the GNU General Public
16 .\" License along with this manual; if not, see
17 .\" <http://www.gnu.org/licenses/>.
20 .\" 2007-04-30: mtk, Added description of epoll_pwait()
22 .TH EPOLL_WAIT 2 2012-08-17 "Linux" "Linux Programmer's Manual"
24 epoll_wait, epoll_pwait \- wait for an I/O event on an epoll file descriptor
27 .B #include <sys/epoll.h>
29 .BI "int epoll_wait(int " epfd ", struct epoll_event *" events ,
30 .BI " int " maxevents ", int " timeout );
31 .BI "int epoll_pwait(int " epfd ", struct epoll_event *" events ,
32 .BI " int " maxevents ", int " timeout ,
33 .BI " const sigset_t *" sigmask );
38 system call waits for events on the
40 instance referred to by the file descriptor
42 The memory area pointed to by
44 will contain the events that will be available for the caller.
51 argument must be greater than zero.
55 argument specifies the minimum number of milliseconds that
58 (This interval will be rounded up to the system clock granularity,
59 and kernel scheduling delays mean that the blocking interval
60 may overrun by a small amount.)
65 to block indefinitely, while specifying a
69 to return immediately, even if no events are available.
77 typedef union epoll_data {
85 uint32_t events; /* Epoll events */
86 epoll_data_t data; /* User data variable */
93 of each returned structure will contain the same data the user set with an
95 .RB ( EPOLL_CTL_ADD ", " EPOLL_CTL_MOD )
98 member will contain the returned event bit field.
100 The relationship between
104 is analogous to the relationship between
111 allows an application to safely wait until either a file descriptor
112 becomes ready or until a signal is caught.
119 ready = epoll_pwait(epfd, &events, maxevents, timeout, &sigmask);
124 executing the following calls:
129 sigprocmask(SIG_SETMASK, &sigmask, &origmask);
130 ready = epoll_wait(epfd, &events, maxevents, timeout);
131 sigprocmask(SIG_SETMASK, &origmask, NULL);
136 argument may be specified as NULL, in which case
143 returns the number of file descriptors ready for the requested I/O, or zero
144 if no file descriptor became ready during the requested
147 When an error occurs,
151 is set appropriately.
156 is not a valid file descriptor.
159 The memory area pointed to by
161 is not accessible with write permissions.
164 The call was interrupted by a signal handler before either any of the
165 requested events occurred or the
176 is less than or equal to zero.
179 was added to the kernel in version 2.6.
180 .\" To be precise: kernel 2.5.44.
181 .\" The interface should be finalized by Linux kernel 2.5.66.
182 Library support is provided in glibc starting with version 2.3.2.
185 was added to Linux in kernel 2.6.19.
186 Library support is provided in glibc starting with version 2.6.
191 While one thread is blocked in a call to
193 it is possible for another thread to add a file descriptor to the waited-upon
196 If the new file descriptor becomes ready,
201 For a discussion of what may happen if a file descriptor in an
203 instance being monitored by
205 is closed in another thread, see
208 In kernels before 2.6.37, a
210 value larger than approximately
212 milliseconds is treated as \-1 (i.e., infinity).
213 Thus, for example, on a system where the
218 this means that timeouts greater than 35.79 minutes are treated as infinity.
220 .BR epoll_create (2),