Commit 2fe64c55 authored by catch's avatar catch

Issues #969998, #1131140 and #1144394: forward port lock improvements from 6.x branch.

parent 00ae2056
......@@ -329,7 +329,8 @@ function dmemcache_key($key, $bin = 'cache') {
static $prefix;
// memcache_key_prefix can be set in settings.php to support site namespaces
// in a multisite environment.
if (empty($prefix)) {
if (!isset($prefix)) {
$prefix = '';
if ($prefix = variable_get('memcache_key_prefix', '')) {
$prefix .= '-';
}
......
......@@ -6,15 +6,10 @@
* See includes/lock.inc for documenation
*/
// Set up a define to make the code more readable, so we know we're setting a
// value for our lock and not simply passing dmemcache a flag.
define('LOCK_VALUE', TRUE);
/**
* Initialize the locking system.
*/
function lock_initialize() {
function lock_init() {
global $locks;
$locks = array();
......@@ -35,19 +30,14 @@ function lock_acquire($name, $timeout = 30) {
// Ensure that the timeout is at least 1 sec. This is a limitation
// imposed by memcached.
$timeout = max($timeout, 1);
$now = microtime(TRUE);
$expire = $now + $timeout;
$timeout = (int) max($timeout, 1);
$result = dmemcache_get($name, 'semaphore');
if ($result && isset($locks[$name]) && $locks[$name] > $now) {
// Only renew the lock if we already set it and it has not expired.
if (dmemcache_set($name, LOCK_VALUE, $timeout, 'semaphore')) {
$locks[$name] = $expire;
}
if (dmemcache_add($name, _lock_id(), $timeout, 'semaphore')) {
$locks[$name] = _lock_id();
}
else if (dmemcache_add($name, LOCK_VALUE, $timeout, 'semaphore')) {
$locks[$name] = $expire;
elseif ($result = dmemcache_get($name, 'semaphore') && isset($locks[$name]) && $locks[$name] == _lock_id()) {
// Only renew the lock if we already set it and it has not expired.
dmemcache_set($name, _lock_id(), $timeout, 'semaphore');
}
else {
// Failed to acquire the lock. Unset the key from the $locks array even if
......@@ -79,7 +69,7 @@ function lock_may_be_available($name) {
* lock. This will block further execution until the lock is available or the
* specified delay in seconds is reached. This should not be used with locks
* that are acquired very frequently, since the lock is likely to be acquired
* again by a different request during the sleep().
* again by a different request while waiting.
*
* @param $name
* The name of the lock.
......@@ -89,12 +79,32 @@ function lock_may_be_available($name) {
* TRUE if the lock holds, FALSE if it is available.
*/
function lock_wait($name, $delay = 30) {
$delay = (int) $delay;
while ($delay--) {
// Pause the process for short periods between calling
// lock_may_be_available(). This prevents hitting the database with constant
// database queries while waiting, which could lead to performance issues.
// However, if the wait period is too long, there is the potential for a
// large number of processes to be blocked waiting for a lock, especially
// if the item being rebuilt is commonly requested. To address both of these
// concerns, begin waiting for 25ms, then add 25ms to the wait period each
// time until it reaches 500ms. After this point polling will continue every
// 500ms until $delay is reached.
// $delay is passed in seconds, but we will be using usleep(), which takes
// microseconds as a parameter. Multiply it by 1 million so that all
// further numbers are equivalent.
$delay = (int) $delay * 1000000;
// Begin sleeping at 25ms.
$sleep = 25000;
while ($delay > 0) {
// This function should only be called by a request that failed to get a
// lock, so we sleep first to give the parallel request a chance to finish
// and release the lock.
sleep(1);
usleep($sleep);
// After each sleep, increase the value of $sleep until it reaches
// 500ms, to reduce the potential for a lock stampede.
$delay = $delay - $sleep;
$sleep = min(500000, $sleep + 25000, $delay);
if (!dmemcache_get($name, 'semaphore')) {
// No longer need to wait.
return FALSE;
......@@ -120,3 +130,29 @@ function lock_release($name) {
unset($locks[$name]);
}
/**
* Generate a unique identifier for locks generated during this request.
*/
function _lock_id() {
static $lock_id;
if (!isset($lock_id)) {
$lock_id = uniqid(mt_rand(), TRUE);
// We only register a shutdown function if a lock is used.
register_shutdown_function('lock_release_all', $lock_id);
}
return $lock_id;
}
/**
* Release all locks acquired by this request.
*/
function lock_release_all($lock_id) {
global $locks;
foreach ($locks as $name => $id) {
$value = dmemcache_get($name, 'semaphore');
if ($value == $id) {
dmemcache_delete($name, 'semaphore');
}
}
}
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