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Full Discussion: How many semaphores?
Top Forums UNIX for Advanced & Expert Users How many semaphores? Post 302144305 by kahuna on Wednesday 7th of November 2007 08:20:54 AM
Old 11-07-2007
Is the requirement that only semaphores be used? It seems to me that all it would take is single semaphore that guards access to a memory location that indicates the last process completed. Each process would wait on the semaphore and once it got access, would check to see if its predecessor had run. If so it would execute and update the last process completed. If not, it would release the semaphore and try again.
 

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SEM_GET(3)								 1								SEM_GET(3)

sem_get - Get a semaphore id

SYNOPSIS
resource sem_get (int $key, [int $max_acquire = 1], [int $perm = 0666], [int $auto_release = 1]) DESCRIPTION
sem_get(3) returns an id that can be used to access the System V semaphore with the given $key. A second call to sem_get(3) for the same key will return a different semaphore identifier, but both identifiers access the same underlying semaphore. PARAMETERS
o $key - o $max_acquire - The number of processes that can acquire the semaphore simultaneously is set to $max_acquire. o $perm - The semaphore permissions. Actually this value is set only if the process finds it is the only process currently attached to the semaphore. o $auto_release - Specifies if the semaphore should be automatically released on request shutdown. RETURN VALUES
Returns a positive semaphore identifier on success, or FALSE on error. CHANGELOG
+--------+-----------------------------------------+ |Version | | | | | | | Description | | | | +--------+-----------------------------------------+ | 4.3.0 | | | | | | | The $auto_release parameter was added. | | | | +--------+-----------------------------------------+ NOTES
Warning When using sem_get(3) to access a semaphore created outside PHP, note that the semaphore must have been created as a set of 3 sema- phores (for example, by specifying 3 as the nsems parameter when calling the C semget() function), otherwise PHP will be unable to access the semaphore. SEE ALSO
sem_acquire(3), sem_release(3), ftok(3). PHP Documentation Group SEM_GET(3)
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