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)
Check Out this Related Man Page
SEM_INIT(3P) POSIX Programmer's Manual SEM_INIT(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_init - initialize an unnamed semaphore (REALTIME) SYNOPSIS
#include <semaphore.h> int sem_init(sem_t *sem, int pshared, unsigned value); DESCRIPTION
The sem_init() function shall initialize the unnamed semaphore referred to by sem. The value of the initialized semaphore shall be value. Following a successful call to sem_init(), the semaphore may be used in subsequent calls to sem_wait(), sem_trywait(), sem_post(), and sem_destroy(). This semaphore shall remain usable until the semaphore is destroyed. If the pshared argument has a non-zero value, then the semaphore is shared between processes; in this case, any process that can access the semaphore sem can use sem for performing sem_wait(), sem_trywait(), sem_post(), and sem_destroy() operations. Only sem itself may be used for performing synchronization. The result of referring to copies of sem in calls to sem_wait(), sem_try- wait(), sem_post(), and sem_destroy() is undefined. If the pshared argument is zero, then the semaphore is shared between threads of the process; any thread in this process can use sem for performing sem_wait(), sem_trywait(), sem_post(), and sem_destroy() operations. The use of the semaphore by threads other than those cre- ated in the same process is undefined. Attempting to initialize an already initialized semaphore results in undefined behavior. RETURN VALUE
Upon successful completion, the sem_init() function shall initialize the semaphore in sem. Otherwise, it shall return -1 and set errno to indicate the error. ERRORS
The sem_init() function shall fail if: EINVAL The value argument exceeds {SEM_VALUE_MAX}. ENOSPC A resource required to initialize the semaphore has been exhausted, or the limit on semaphores ( {SEM_NSEMS_MAX}) has been reached. EPERM The process lacks the appropriate privileges to initialize the semaphore. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The sem_init() function is part of the Semaphores option and need not be available on all implementations. RATIONALE
Although this volume of IEEE Std 1003.1-2001 fails to specify a successful return value, it is likely that a later version may require the implementation to return a value of zero if the call to sem_init() is successful. FUTURE DIRECTIONS
None. SEE ALSO
sem_destroy(), 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_INIT(3P)