SunshinePHP Developer Conference 2015

sem_release

(PHP 4, PHP 5)

sem_releaseセマフォを解放する

説明

bool sem_release ( resource $sem_identifier )

sem_release() は、そのセマフォが コール元のプロセスにより現在確保されている場合、解放します。 そうでない場合、警告が表示されます。

セマフォを解放した後、再び確保するには、sem_acquire() をコールします。

パラメータ

sem_identifier

sem_get() が返すセマフォリソースハンドル。

返り値

成功した場合に TRUE を、失敗した場合に FALSE を返します。

参考

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User Contributed Notes 2 notes

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1
danno at circumsolutions dot com
13 years ago
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.
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apua at communiplex dot com
14 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.
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