sem_trywait(3p) [posix man page]

SEM_TRYWAIT(3P) 					     POSIX Programmer's Manual						   SEM_TRYWAIT(3P)

PROLOG

       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME

       sem_trywait, sem_wait -- lock a semaphore

SYNOPSIS

       #include <semaphore.h>

       int sem_trywait(sem_t *sem);
       int sem_wait(sem_t *sem);

DESCRIPTION

       The sem_trywait() function shall lock the semaphore referenced by sem only if the semaphore is currently not locked; that is, if the  sema-
       phore value is currently positive. Otherwise, it shall not lock the semaphore.

       The sem_wait() function shall lock the semaphore referenced by sem by performing a semaphore lock operation on that semaphore. If the sema-
       phore value is currently zero, then the calling thread shall not return from the call to sem_wait() until it either locks the semaphore	or
       the call is interrupted by a signal.

       Upon  successful  return,  the state of the semaphore shall be locked and shall remain locked until the sem_post() function is executed and
       returns successfully.

       The sem_wait() function is interruptible by the delivery of a signal.

RETURN VALUE

       The sem_trywait() and sem_wait() functions shall return zero if the calling process successfully performed the semaphore lock operation	on
       the  semaphore  designated  by  sem.   If  the call was unsuccessful, the state of the semaphore shall be unchanged, and the function shall
       return a value of -1 and set errno to indicate the error.

ERRORS

       The sem_trywait() function shall fail if:

       EAGAIN The semaphore was already locked, so it cannot be immediately locked by the sem_trywait() operation.

       The sem_trywait() and sem_wait() functions may fail if:

       EDEADLK
	      A deadlock condition was detected.

       EINTR  A signal interrupted this function.

       EINVAL The sem argument does not refer to a valid semaphore.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       Applications using these functions may be subject to priority inversion, as discussed in the Base Definitions volume of POSIX.1-2008,  Sec-
       tion 3.287, Priority Inversion.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       semctl(), semget(), semop(), sem_post(), sem_timedwait()

       The Base Definitions volume of POSIX.1-2008, Section 3.287, Priority Inversion, Section 4.11, Memory Synchronization, <semaphore.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
       event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013							   SEM_TRYWAIT(3P)

Check Out this Related Man Page

sem_wait(3)						     Library Functions Manual						       sem_wait(3)

NAME

       sem_wait, sem_trywait - Performs (or conditionally performs) a semaphore lock (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <semaphore.h>

       int sem_wait (
       sem_t *sem);

       int sem_trywait (
       sem_t *sem);

PARAMETERS

       sem	 Specifies a pointer to the semaphore to be locked.

DESCRIPTION

       The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero,
       the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.

       The sem_trywait function locks a semaphore only if the semaphore is currently not locked.  If the semaphore value is zero, the  sem_trywait
       function returns without locking the semaphore.

       These  functions  help ensure that the resource associated with the semaphore cannot be accessed by other processes.  The semaphore remains
       locked until the process unlocks it with a call to the sem_post function.

       Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.

RETURN VALUES

       If the sem_wait or sem_trywait function returns successfully, a value of 0 (zero) is returned and the function executes the semaphore  lock
       operation.

       On  an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains
       unchanged.

ERRORS

       The sem_wait and sem_trywait functions fail under the following conditions:

       [EAGAIN]       The semaphore was already locked and cannot be locked by the sem_trywait operation (sem_trywait only).

       [EINTR]	      A signal interrupted this function.

       [EINVAL]       The sem argument does not refer to a valid semaphore.

RELATED INFORMATION

       Functions: sem_post(3)

       Guide to Realtime Programming delim off

																       sem_wait(3)

Linux and UNIX Man Pages

sem_trywait(3p) [posix man page]

Check Out this Related Man Page