function lock_acquire
Acquire (or renew) a lock, but do not block if it fails.
Parameters
$name: The name of the lock. Limit of name's length is 255 characters.
$timeout: A number of seconds (float) before the lock expires (minimum of 0.001).
Return value
TRUE if the lock was acquired, FALSE if it failed.
Related topics
18 calls to lock_acquire()
- DrupalCacheArray::set in includes/
bootstrap.inc - Writes a value to the persistent cache immediately.
- DrupalWebTestCase::storeSetupCache in modules/
simpletest/ drupal_web_test_case.php - Store the installation setup to a cache.
- drupal_cron_run in includes/
common.inc - Executes a cron run when called.
- FieldInfo::getBundleExtraFields in modules/
field/ field.info.class.inc - Retrieves the "extra fields" for a bundle.
- FieldInfo::getBundleInstances in modules/
field/ field.info.class.inc - Retrieves the instances for a bundle.
File
-
includes/
lock.inc, line 121
Code
function lock_acquire($name, $timeout = 30.0) {
global $locks;
// Insure that the timeout is at least 1 ms.
$timeout = max($timeout, 0.001);
$expire = microtime(TRUE) + $timeout;
if (isset($locks[$name])) {
// Try to extend the expiration of a lock we already acquired.
$success = (bool) db_update('semaphore')->fields(array(
'expire' => $expire,
))
->condition('name', $name)
->condition('value', _lock_id())
->execute();
if (!$success) {
// The lock was broken.
unset($locks[$name]);
}
return $success;
}
else {
// Optimistically try to acquire the lock, then retry once if it fails.
// The first time through the loop cannot be a retry.
$retry = FALSE;
// We always want to do this code at least once.
do {
try {
db_insert('semaphore')->fields(array(
'name' => $name,
'value' => _lock_id(),
'expire' => $expire,
))
->execute();
// We track all acquired locks in the global variable.
$locks[$name] = TRUE;
// We never need to try again.
$retry = FALSE;
} catch (PDOException $e) {
// Suppress the error. If this is our first pass through the loop,
// then $retry is FALSE. In this case, the insert must have failed
// meaning some other request acquired the lock but did not release it.
// We decide whether to retry by checking lock_may_be_available()
// Since this will break the lock in case it is expired.
$retry = $retry ? FALSE : lock_may_be_available($name);
}
// We only retry in case the first attempt failed, but we then broke
// an expired lock.
} while ($retry);
}
return isset($locks[$name]);
}
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