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PhpDig is a PHP MySQL based
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sem_get — Returns an identifier for the semaphore with the given key.


int sem_get(key[, max_acquire][, permissions]);
int key: Key of the semaphore for which to get an IDKey of the semaphore for which to get an ID
int max_acquire (optional): Maximum number of processes that can acquire this semaphore simultaneously
int permissions (optional): Permissions for the semaphore


Semaphore ID if successful; FALSE otherwise


sem_get() creates and returns an identifier that can be used to access the semaphore whose key is given in key . This semaphore can then be simultaneously acquired by at most the number of processes defined by max_acquire , which defaults to 1. The semaphore will have the permissions given by the permissions parameter, which defaults to 0666.

key is a unique integer identifier that you supply. The major restriction is that if you want to have multiple scripts accessing the same semaphore, they all need to use the same key to get its ID.


PHP 3 since 3.0.6, PHP 4

See also

See also sem_acquire() , sem_release()


Example 1171. Get a semaphore ID

define('MY_SEMAPHORE_KEY', 30);
if (!$sem_id = @sem_get(MY_SEMAPHORE_KEY)) {
    echo "Could not get ID for the semaphore; reason: $php_errormsg\n";

PHP Functions Essential Reference. Copyright © 2002 by New Riders Publishing (Authors: Zak Greant, Graeme Merrall, Torben Wilson, Brett Michlitsch). This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at The authors of this book have elected not to choose any options under the OPL. This online book was obtained from and is designed to provide information about the PHP programming language, focusing on PHP version 4.0.4 for the most part. The information is provided on an as-is basis, and no warranty or fitness is implied. All persons and entities shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from the information contained in this book.

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