sem_trywait(3p) [centos 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 (REALTIME)

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() and sem_wait() functions shall fail if:

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

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

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

       EDEADLK
	      A deadlock condition was detected.

       EINTR  A signal interrupted this function.

       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
       IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.

       The sem_trywait() and sem_wait() functions are part of the Semaphores option and need not be provided on all implementations.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       semctl(), semget(), semop(), sem_post(), sem_timedwait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. 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 Standard is the referee document. The original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							   SEM_TRYWAIT(3P)

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 (REALTIME)

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() and sem_wait() functions shall fail if:

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

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

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

       EDEADLK
	      A deadlock condition was detected.

       EINTR  A signal interrupted this function.

       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
       IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.

       The sem_trywait() and sem_wait() functions are part of the Semaphores option and need not be provided on all implementations.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       semctl(), semget(), semop(), sem_post(), sem_timedwait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
       Electrical  and	Electronics  Engineers, Inc and The Open Group. 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 Standard is the referee document. The original Standard can  be  obtained
       online at http://www.opengroup.org/unix/online.html .

IEEE
/The Open Group						       2003							   SEM_TRYWAIT(3P)