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1. drupal
   1. drupal6

Acquire (or renew) a lock, but do not block if it fails.

Übergabeparameter

$name The name of the lock.

$timeout A number of seconds (float) before the lock expires.

Rückgabewert

TRUE if the lock was acquired, FALSE if it failed.

Verwandte Themen

Functions to coordinate long-running operations across requests.

In most environments, multiple Drupal page requests (a.k.a. threads or processes) will execute in parallel. This leads to potential conflicts or race conditions when two requests execute the same code at the same time. A common example of this is a…

Code

includes/lock.inc, line 97

<?php
function lock_acquire($name, $timeout = 30.0) {
  global $locks;

  // Insure that the timeout is at least 1 ms.
  $timeout = max($timeout, 0.001);
  list($usec, $sec) = explode(' ', microtime());
  $expire = (float) $usec + (float) $sec + $timeout;
  if (isset($locks[$name])) {
    // Try to extend the expiration of a lock we already acquired.
    if (!db_result(db_query("UPDATE {semaphore} SET expire = %f WHERE name = '%s' AND value = '%s'", $expire, $name, _lock_id()))) {
      // The lock was broken.
      unset($locks[$name]);
    }
  }
  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 {
      if (@db_query("INSERT INTO {semaphore} (name, value, expire) VALUES ('%s', '%s', %f)", $name, _lock_id(), $expire)) {
        // We track all acquired locks in the global variable.
        $locks[$name] = TRUE;
        // We never need to try again.
        $retry = FALSE;
      }
      else {
        // 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]);
}
?>