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sem_post(2) [hpux man page]

sem_post(2)							System Calls Manual						       sem_post(2)

NAME
sem_post - unlock a POSIX semaphore SYNOPSIS
DESCRIPTION
is used to post the semaphore referenced by sem. The calling thread will not return from its call to unless it can either: increment the semaphore value, if there are no blocked threads on this semaphore; give the semaphore to a blocked thread, if there are any blocked threads on this semaphore; or have an error condition. If the semaphore value is < 0, the semaphore has blocked threads, waiting for it to become available (the absolute value of the semaphore's value indicates the number of waiters at that moment). If the semaphore value is >= 0, the semaphore has no waiters. If the semaphore has no waiters at the time its value is checked, the semaphore's value will be atomically incremented, with respect to the checking of its value, up to its maximum value as specified by If the semaphore has waiters at the time its value is checked, the semaphore value is not changed. Instead, the calling thread will attempt to wake up a waiter. If the semaphore has waiters having realtime priori- ties, the thread must wake up the highest priority waiter. Otherwise the thread at the head of the channel queue is woken up. When a waiter is successfully woken, the semaphore being posted will be given to the woken waiter. In other words, the state of the sema- phore remains unchanged. Instead, the semaphore being posted will be inherited by the waiter being woken from this call to 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 this operation. The routine may be called asyn- chronously, i.e. from a signal handler. To use this function, link in the realtime library by specifying on the compiler or linker command line. EXAMPLES
The following call to will post the semaphore sem. RETURN VALUE
A successful call to will return 0 and the calling thread would have posted the semaphore. Otherwise, the call to will return -1 with errno set to the appropriate value of the error condition. ERRORS
fails and does not perform the requested operation if any of the following conditions are encountered: [EPERM] The calling process does not have the privileges necessary to post the semaphore. [EINVAL] The argument sem does not refer to a valid semaphore. SEE ALSO
<semaphore.h>. STANDARDS CONFORMANCE
sem_post(2)

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sem_init(2)							System Calls Manual						       sem_init(2)

NAME
sem_init - initialize an unnamed POSIX semaphore SYNOPSIS
DESCRIPTION
is used to initialize an unnamed semaphore. A successful call to will create a new unnamed semaphore referred to by sem, if one does not exist, initialize the unnamed semaphore descriptor, referred to by sem, to the non-negative value specified by value. If the unnamed sema- phore already exists, i.e. created by a previous call to it is re-initialized only if its current value is equal to its initial value (set by the last successful call to If so, the initial value of the unnamed semaphore is re-initialized to the value argument. Otherwise, the call fails. The argument pshared specifies if the unnamed semaphore is sharable with other processes. If pshared is equal to 0, the unnamed semaphore is not shared with other processes. If pshared is non-zero, the unnamed semaphore is sharable with any processes that can access sem. The access mode specified for the unnamed semaphore allows read and write permissions to all processes. If the calling process may attach to the shared structure, it is assumed it may operate on the semaphore. To use this function, link in the realtime library by specifying on the compiler or linker command line. EXAMPLES
The following call to will create a new unnamed semaphore referred to by sem, if one does not exist, initialize the unnamed semaphore descriptor, referred to by sem, to the non-negative value specified by value. RETURN VALUE
If the semaphore was created and initialized, returns 0 to the caller. If the semaphore could not be created/initialized, the call returns -1 and sets to indicate the error. ERRORS
fails and does not perform the requested operation if any of the following conditions are encountered: [EPERM] The calling process does not have the privileges necessary to initialize the semaphore. [EBUSY] There are threads currently blocked on the semaphore or there are outstanding locks held on the semaphore. [EINVAL] The argument value is greater than [ENOSPC] There are insufficient resources to perform the operation or the upper limit on the number of semaphores is reached. SEE ALSO
sem_destroy(2), sem_post(2), sem_trywait(2), sem_wait(2), <semaphore.h>. STANDARDS CONFORMANCE
sem_init(2)
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