--- /dev/null
+<?php
+
+namespace Drupal\Core\Lock;
+
+/**
+ * @defgroup lock Locking mechanisms
+ * @{
+ * Functions to coordinate long 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. For
+ * instance, some implementations of hook_cron() implicitly assume they are
+ * running only once, rather than having multiple calls in parallel. To prevent
+ * problems with such code, the cron system uses a locking process to ensure
+ * that cron is not started again if it is already running.
+ *
+ * To avoid these types of conflicts, Drupal has a cooperative, advisory lock
+ * system. Any long-running operation that could potentially be attempted in
+ * parallel by multiple requests should try to acquire a lock before
+ * proceeding. By obtaining a lock, one request notifies any other requests that
+ * a specific operation is in progress which must not be executed in parallel.
+ *
+ * To use this API, pick a unique name for the lock. A sensible choice is the
+ * name of the function performing the operation. Here is a simple example:
+ * @code
+ * function mymodule_long_operation() {
+ * $lock = \Drupal::lock();
+ * if ($lock->acquire('mymodule_long_operation')) {
+ * // Do the long operation here.
+ * // ...
+ * $lock->release('mymodule_long_operation');
+ * }
+ * }
+ * @endcode
+ *
+ * If a function acquires a lock it should always release it when the operation
+ * is complete by calling $lock->release(), as in the example.
+ *
+ * A function that has acquired a lock may attempt to renew a lock (extend the
+ * duration of the lock) by calling $lock->acquire() again during the operation.
+ * Failure to renew a lock is indicative that another request has acquired the
+ * lock, and that the current operation may need to be aborted.
+ *
+ * If a function fails to acquire a lock it may either immediately return, or
+ * it may call $lock->wait() if the rest of the current page request requires
+ * that the operation in question be complete. After $lock->wait() returns, the
+ * function may again attempt to acquire the lock, or may simply allow the page
+ * request to proceed on the assumption that a parallel request completed the
+ * operation.
+ *
+ * $lock->acquire() and $lock->wait() will automatically break (delete) a lock
+ * whose duration has exceeded the timeout specified when it was acquired.
+ *
+ * The following limitations in this implementation should be carefully noted:
+ * - Time: Timestamps are derived from the local system clock of the environment
+ * the code is executing in. The orderly progression of time from this
+ * viewpoint can be disrupted by external events such as NTP synchronization
+ * and operator intervention. Where multiple web servers are involved in
+ * serving the site, they will have their own independent clocks, introducing
+ * another source of error in the time keeping process. Timeout values applied
+ * to locks must therefore be considered approximate, and should not be relied
+ * upon.
+ * - Uniqueness: Uniqueness of lock names is not enforced. The impact of the
+ * use of a common lock name will depend on what processes and resources the
+ * lock is being used to manage.
+ * - Sharing: There is limited support for resources shared across sites.
+ * The locks are stored as rows in the semaphore table and, as such, they
+ * have the same visibility as the table. If resources managed by a lock are
+ * shared across sites then the semaphore table must be shared across sites
+ * as well. This is a binary situation: either all resources are shared and
+ * the semaphore table is shared or no resources are shared and the semaphore
+ * table is not shared. Mixed mode operation is not supported.
+ *
+ * @} End of "defgroup lock".
+ */
+
+/**
+ * Lock backend interface.
+ *
+ * @ingroup lock
+ */
+interface LockBackendInterface {
+
+ /**
+ * Acquires a lock.
+ *
+ * @param string $name
+ * Lock name. Limit of name's length is 255 characters.
+ * @param float $timeout
+ * (optional) Lock lifetime in seconds. Defaults to 30.0.
+ *
+ * @return bool
+ */
+ public function acquire($name, $timeout = 30.0);
+
+ /**
+ * Checks if a lock is available for acquiring.
+ *
+ * @param string $name
+ * Lock to acquire.
+ *
+ * @return bool
+ */
+ public function lockMayBeAvailable($name);
+
+ /**
+ * Waits a short amount of time before a second lock acquire attempt.
+ *
+ * While this method is subject to have a generic implementation in abstract
+ * backend implementation, some backends may provide non blocking or less I/O
+ * intensive wait mechanism: this is why this method remains on the backend
+ * interface.
+ *
+ * @param string $name
+ * Lock name currently being locked.
+ * @param int $delay
+ * Milliseconds to wait for. Defaults to 30.
+ *
+ * @return bool
+ * TRUE if the lock holds, FALSE if it may be available. You still need to
+ * acquire the lock manually and it may fail again.
+ */
+ public function wait($name, $delay = 30);
+
+ /**
+ * Releases the given lock.
+ *
+ * @param string $name
+ */
+ public function release($name);
+
+ /**
+ * Releases all locks for the given lock token identifier.
+ *
+ * @param string $lockId
+ * (optional) If none given, remove all locks from the current page.
+ * Defaults to NULL.
+ */
+ public function releaseAll($lockId = NULL);
+
+ /**
+ * Gets the unique page token for locks.
+ *
+ * Locks will be wiped out at the end of each page request on a token basis.
+ *
+ * @return string
+ */
+ public function getLockId();
+
+}
projects / yaffs-website / blobdiff