* @ingroup Cache
*/
abstract class BagOStuff implements LoggerAwareInterface {
- private $debugMode = false;
-
+ /** @var array[] Lock tracking */
+ protected $locks = array();
/** @var integer */
protected $lastError = self::ERR_NONE;
- /**
- * @var LoggerInterface
- */
+ /** @var LoggerInterface */
protected $logger;
+ /** @var bool */
+ private $debugMode = false;
+
/** Possible values for getLastError() */
const ERR_NONE = 0; // no error
const ERR_NO_RESPONSE = 1; // no response
$this->clearLastError();
$currentValue = $this->get( $key );
- if ( !$this->getLastError() ) {
+ if ( $this->getLastError() ) {
+ $success = false;
+ } else {
// Derive the new value from the old value
$value = call_user_func( $callback, $this, $key, $currentValue );
-
if ( $value === false ) {
$success = true; // do nothing
} else {
}
/**
+ * Acquire an advisory lock on a key string
+ *
+ * Note that if reentry is enabled, duplicate calls ignore $expiry
+ *
* @param string $key
* @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
- * @param int $expiry Lock expiry [optional]
+ * @param int $expiry Lock expiry [optional]; 1 day maximum
+ * @param string $rclass Allow reentry if set and the current lock used this value
* @return bool Success
*/
- public function lock( $key, $timeout = 6, $expiry = 6 ) {
+ public function lock( $key, $timeout = 6, $expiry = 6, $rclass = '' ) {
+ // Avoid deadlocks and allow lock reentry if specified
+ if ( isset( $this->locks[$key] ) ) {
+ if ( $rclass != '' && $this->locks[$key]['class'] === $rclass ) {
+ ++$this->locks[$key]['depth'];
+ return true;
+ } else {
+ return false;
+ }
+ }
+
+ $expiry = min( $expiry ?: INF, 86400 );
+
$this->clearLastError();
$timestamp = microtime( true ); // starting UNIX timestamp
if ( $this->add( "{$key}:lock", 1, $expiry ) ) {
- return true;
- } elseif ( $this->getLastError() ) {
- return false;
+ $locked = true;
+ } elseif ( $this->getLastError() || $timeout <= 0 ) {
+ $locked = false; // network partition or non-blocking
+ } else {
+ $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
+ $sleep = 2 * $uRTT; // rough time to do get()+set()
+
+ $attempts = 0; // failed attempts
+ do {
+ if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
+ // Exponentially back off after failed attempts to avoid network spam.
+ // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
+ $sleep *= 2;
+ }
+ usleep( $sleep ); // back off
+ $this->clearLastError();
+ $locked = $this->add( "{$key}:lock", 1, $expiry );
+ if ( $this->getLastError() ) {
+ $locked = false; // network partition
+ break;
+ }
+ } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
}
- $uRTT = ceil( 1e6 * ( microtime( true ) - $timestamp ) ); // estimate RTT (us)
- $sleep = 2 * $uRTT; // rough time to do get()+set()
-
- $locked = false; // lock acquired
- $attempts = 0; // failed attempts
- do {
- if ( ++$attempts >= 3 && $sleep <= 5e5 ) {
- // Exponentially back off after failed attempts to avoid network spam.
- // About 2*$uRTT*(2^n-1) us of "sleep" happen for the next n attempts.
- $sleep *= 2;
- }
- usleep( $sleep ); // back off
- $this->clearLastError();
- $locked = $this->add( "{$key}:lock", 1, $expiry );
- if ( $this->getLastError() ) {
- return false;
- }
- } while ( !$locked && ( microtime( true ) - $timestamp ) < $timeout );
+ if ( $locked ) {
+ $this->locks[$key] = array( 'class' => $rclass, 'depth' => 1 );
+ }
return $locked;
}
/**
+ * Release an advisory lock on a key string
+ *
* @param string $key
* @return bool Success
*/
public function unlock( $key ) {
- return $this->delete( "{$key}:lock" );
+ if ( isset( $this->locks[$key] ) && --$this->locks[$key]['depth'] <= 0 ) {
+ unset( $this->locks[$key] );
+
+ return $this->delete( "{$key}:lock" );
+ }
+
+ return true;
+ }
+
+ /**
+ * Get a lightweight exclusive self-unlocking lock
+ *
+ * Note that the same lock cannot be acquired twice.
+ *
+ * This is useful for task de-duplication or to avoid obtrusive
+ * (though non-corrupting) DB errors like INSERT key conflicts
+ * or deadlocks when using LOCK IN SHARE MODE.
+ *
+ * @param string $key
+ * @param int $timeout Lock wait timeout; 0 for non-blocking [optional]
+ * @param int $expiry Lock expiry [optional]; 1 day maximum
+ * @param string $rclass Allow reentry if set and the current lock used this value
+ * @return ScopedCallback|null Returns null on failure
+ * @since 1.26
+ */
+ final public function getScopedLock( $key, $timeout = 6, $expiry = 30, $rclass = '' ) {
+ $expiry = min( $expiry ?: INF, 86400 );
+
+ if ( !$this->lock( $key, $timeout, $expiry, $rclass ) ) {
+ return null;
+ }
+
+ $lSince = microtime( true ); // lock timestamp
+ // PHP 5.3: Can't use $this in a closure
+ $that = $this;
+ $logger = $this->logger;
+
+ return new ScopedCallback( function() use ( $that, $logger, $key, $lSince, $expiry ) {
+ $latency = .050; // latency skew (err towards keeping lock present)
+ $age = ( microtime( true ) - $lSince + $latency );
+ if ( ( $age + $latency ) >= $expiry ) {
+ $logger->warning( "Lock for $key held too long ($age sec)." );
+ return; // expired; it's not "safe" to delete the key
+ }
+ $that->unlock( $key );
+ } );
}
/**
dépôts / lhc / web / wiklou.git / blobdiff