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API C MYSQL vs lock table ???
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sem_wait(2) System Calls Manual sem_wait(2) NAME
sem_wait, sem_trywait - lock a POSIX semaphore SYNOPSIS
DESCRIPTION
is used to lock a semaphore. The calling thread will not return from its call to until one of the following events occur: it successfully obtains a lock on the semaphore; it is interrupted by a signal or an error condition occurs. is used to lock a semaphore, if it is available. The value of the semaphore sem is checked at some unspecified time during the call. If the semaphore is available at the time its value is checked, the calling thread will atomically, with respect to the checking of the value, lock the semaphore. The thread will now own a lock on the semaphore; the call will return successfully. If the semaphore is unavailable at the time its value is checked, then the call returns -1 with errno set to EAGAIN. If the specified semaphore referred to by sem is a named semaphore, then this semaphore must have been opened by the calling process with The calling process must have both read and write permissions on the semaphore to perform these operations. The semaphore will be locked upon successful return and will stay locked until it is explicitly released by a call to To use this function, link in the realtime library by specifying on the compiler or linker command line. EXAMPLES
The following call to will lock the semaphore sem. The following call to will lock the semaphore sem, if it is available. RETURN VALUE
A successful call to will return 0 and the calling thread will then own a lock on the semaphore. Otherwise, the call to will return -1 with errno set to the appropriate value of the error condition. A successful call to will return 0, if the semaphore was available and the calling thread was able to lock the semaphore. Otherwise, the call to will return -1 with errno set to the appropriate value of the error condition. ERRORS
and fail and do not perform the requested operation if any of the following conditions are encountered: [EPERM] The calling process does not have the privileges necessary to lock the semaphore. [EAGAIN] The semaphore was not available and hence could not be locked by This error condition only occurs in [EINVAL] The argument sem does not refer to a valid semaphore. [EINTR] The function was interrupted by a signal SEE ALSO
sem_post(2), <semaphore.h>. STANDARDS CONFORMANCE
sem_wait(2)
API C MYSQL vs lock table ???