man3/sem_post.3

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  23 .TH SEM_POST 3 2006-03-25 "Linux 2.6.16" "Linux Programmer's Manual"
  24 .SH NAME
  25 sem_post \- unlock a semaphore
  26 .SH SYNOPSIS
  27 .nf
  28 .B #include <semaphore.h>
  29 .sp
  30 .BI "int sem_post(sem_t *" sem );
  31 .fi
  32 .SH DESCRIPTION
  33 .BR sem_post ()
  34 increments (unlocks) the semaphore pointed to by
  35 .IR sem .
  36 If the semaphore's value consequently becomes greater than zero,
  37 then another process or thread blocked in a
  38 .BR sem_wait (3)
  39 call will be woken up and proceed to lock the semaphore.
  40 .SH RETURN VALUE
  41 .BR sem_post ()
  42 returns 0 on success;
  43 on error, the value of the semaphore is left unchanged,
  44 \-1 is returned, and
  45 .I errno
  46 is set to indicate the error.
  47 .SH ERRORS
  48 .TP
  49 .B EINVAL
  50 .I sem
  51 is not a valid semaphore.
  52 .SH CONFORMING TO
  53 POSIX.1-2001.
  54 .SH NOTES
  55 .BR sem_post ()
  56 is async-signal-safe:
  57 it may be safely called within a signal handler.
  58 .SH "SEE ALSO"
  59 .BR sem_getvalue (3),
  60 .BR sem_wait (3),
  61 .BR sem_overview (7)