If you want to implement this sort of semaphore access (which is usually what is needed if doing ipc) one thing you can do is create shared memory which is simply an int. Use this int between processes as the value of the semaphore. You can write wrapper functions which use this to allow you to do the desired readers-writers stuff or just use the shared memory plain. I wouldn't be too worried about race conditions in this case as the shared memory is only an int. If you are worried about race conditions, the wrapper functions for doing the semaphore stuff could actually use a semaphore to elimate any race conditions. Also, an added bonus of doing it this way is you can check the value of the int.
sem_release
(PHP 4, PHP 5, PHP 7, PHP 8)
sem_release — Libère un sémaphore
Description
sem_release() libère le sémaphore
sem_identifier, s'il a été réservé par le
processus courant, sinon génère une erreur.
Après libération du sémaphore, sem_acquire() peut être appelé pour le réserver à nouveau.
Valeurs de retour
Cette fonction retourne true en cas de succès ou false si une erreur survient.
Historique
| Version | Description |
|---|---|
| 8.0.0 |
semaphore attend désormais une SysvSemaphore;
auparavant, une resource était attendue.
|
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User Contributed Notes 2 notes
danno at circumsolutions dot com ¶
23 years ago
apua at communiplex dot com ¶
25 years ago
The fact that sem_release only resease the semaphore if it is currently acquired by the calling process is, in fact, a misfeature since sometimes (eg in a readers-writers implementation) it is desirable to release a semaphore acquired by another process. In C you can do that.
I'm telling this because I was trying to write a chat app in php3 made of two programs: a listener and a speaker. The speaker releases a semaphore to inform that there is a new message in a shared memory var. And listeners wait in that semaphore before outputting the message.
