sem_getvalue(3p) [centos man page]
SEM_GETVALUE(3P) POSIX Programmer's Manual SEM_GETVALUE(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_getvalue - get the value of a semaphore (REALTIME) SYNOPSIS
#include <semaphore.h> int sem_getvalue(sem_t *restrict sem, int *restrict sval); DESCRIPTION
The sem_getvalue() function shall update the location referenced by the sval argument to have the value of the semaphore referenced by sem without affecting the state of the semaphore. The updated value represents an actual semaphore value that occurred at some unspecified time during the call, but it need not be the actual value of the semaphore when it is returned to the calling process. If sem is locked, then the object to which sval points shall either be set to zero or to a negative number whose absolute value represents the number of processes waiting for the semaphore at some unspecified time during the call. RETURN VALUE
Upon successful completion, the sem_getvalue() function shall return a value of zero. Otherwise, it shall return a value of -1 and set errno to indicate the error. ERRORS
The sem_getvalue() function shall fail if: EINVAL The sem argument does not refer to a valid semaphore. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The sem_getvalue() function is part of the Semaphores option and need not be available on all implementations. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
semctl(), semget(), semop(), sem_post(), sem_timedwait(), sem_trywait(), sem_wait(), 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_GETVALUE(3P)
Check Out this Related 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)