DB_Lock.php — Pods – Custom Content Types and Fields 2.9.19.4

pods / tribe-common / src / Tribe / DB_Lock.php

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DB_Lock.php

353 lines

1	<?php
2	/**
3	* Manages database locks using MySQL fucntions or queries.
4	*
5	* The MySQL functions used by this class are `GET_LOCK`, `IS_FREE_LOCK` and `RELEASE_LOCK`.
6	* The functions are part of MySQL 5.6 and in line with WordPress minimum requirement of MySQL version (5.6).
7	*
8	* @see https://dev.mysql.com/doc/refman/5.6/en/locking-functions.html#function_get-lock
9	*
10	* @since 4.12.6
11	*
12	* @package Tribe
13	*/
14
15	namespace Tribe;
16
17	/**
18	* Class DB_Lock
19	*
20	* @since 4.12.6
21	*
22	* @package Tribe
23	*/
24	class DB_Lock {
25
26	/**
27	* The prefix of the options used to manage the database lock without use of MySQL functions
28	* in the options table.
29	*
30	* @since 4.12.6
31	*
32	* @var string
33	*/
34	public static $db_lock_option_prefix = 'tribe_db_lock_';
35
36	/**
37	* A map, shared among all instance of this trait in the session, of the currently held locks the
38	* time the locks where acquired, a UNIX timestamp w/ micro-seconds.
39	*
40	* @since 4.12.6
41	*
42	* @var array<string,float>
43	*/
44	protected static $held_db_locks = [];
45
46	/**
47	* Prunes the stale locks stored in the options table.
48	*
49	* @since 4.12.6
50	*
51	* @return int\|false The number of pruned locks, or `false` to indicate the query to prune the locks generated
52	* an error (logged).
53	*/
54	public static function prune_stale_db_locks() {
55	global $wpdb;
56	$prefix = static::$db_lock_option_prefix;
57	$affected_rows = $wpdb->query(
58	"DELETE FROM {$wpdb->options}
59	WHERE option_name LIKE '{$prefix}%'
60	AND option_value < ( UNIX_TIMESTAMP() - 86400 )"
61	);
62
63	if ( false === $affected_rows ) {
64	$log_data = [
65	'message' => 'Error while trying to prune stale db locks.',
66	'error' => $wpdb->last_error
67	];
68	do_action( 'tribe_log', 'error', __CLASS__, $log_data );
69
70	return false;
71	}
72
73	return (int) $affected_rows;
74	}
75
76	/**
77	* Acquires a db lock.
78	*
79	* To ensure back-compatibility with MySQL 5.6, the lock will hash the lock key using SHA1.
80	*
81	* @since 4.12.6
82	*
83	* @param string $lock_key The name of the db lock key to acquire.
84	*
85	* @return bool Whether the lock acquisition was successful or not.
86	*/
87	public function acquire_db_lock( $lock_key ) {
88	/**
89	* Filters the timeout, in seconds, of the database lock acquisition attempts.
90	*
91	* The timeout will not be used when locks are managed using queries in place of
92	* MySQL functions.
93	*
94	* @since 4.12.6
95	*
96	* @param int $timeout The timeout, in seconds, of the lock acquisition attempt.
97	* @param string $lock_key The lock key the target of the acquisition attempt.
98	* @param static $this The object that's trying to acquire the lock by means of the trait.
99	*/
100	$timeout = apply_filters( 'tribe_db_lock_timeout', 3, $lock_key, $this );
101
102	if ( $this->manage_db_lock_w_mysql_functions() ) {
103	return $this->acquire_db_lock_w_mysql_functions( $lock_key, $timeout );
104	}
105
106	return $this->acquire_db_lock_w_queries( $lock_key );
107	}
108
109	/**
110	* Returns whether the traits should try to acquire and release locks using MySQL `GET_LOCK` and `RELEASE_LOCK`
111	* functions or not.
112	*
113	* If not, then the trait will manage the locks by means of direct SQL queries on the options table.
114	*
115	* @since 4.12.6
116	*
117	* @return bool Whether the trait should use MySQL functions to manage the locks, or not.
118	*/
119	protected function manage_db_lock_w_mysql_functions() {
120	/**
121	* Filters whether the database lock should be acquired using the `GET_LOCK` and `RELEASE_LOCK`
122	* MySQL functions or not.
123	*
124	* If the filter returns a falsy value, then the trait will attempt to manage locks using `SELECT`
125	* and `UPDATE` queries on the options table.
126	*
127	* @since 4.12.6
128	*/
129	return tribe_is_truthy( apply_filters( 'tribe_db_lock_use_msyql_functions', true ) );
130	}
131
132	/**
133	* Tries to acquire the database lock using MySQL functions (`GET_LOCK` and `IS_FREE_LOCK`).
134	*
135	* @since 4.12.6
136	*
137	* @param string $lock_key The lock key to try and acquire the lock for.
138	* @param int $timeout The timeout, in seconds, to try and acquire the lock.
139	*
140	* @return bool Whether the lock was acquired or not.
141	*/
142	protected function acquire_db_lock_w_mysql_functions( $lock_key, $timeout ) {
143	/*
144	* On MySQL 5.6 if a session (a db connection) fires two requests of `GET_LOCK`, the lock is
145	* implicitly released and re-acquired.
146	* While this will not cause issues in the context of different db sessions (e.g. two diff. PHP
147	* processes competing for a lock), it would cause issues when the lock acquisition is attempted
148	* in the context of the same PHP process.
149	* To avoid a read-what-you-write issue in the context of the same request, we check if the lock is
150	* free, using `IS_FREE_LOCK` first.
151	*/
152
153	global $wpdb;
154
155	$free = $wpdb->get_var(
156	$wpdb->prepare( 'SELECT IS_FREE_LOCK( SHA1( %s ) )', $lock_key )
157	);
158
159	if ( ! $free ) {
160	return false;
161	}
162
163	$acquired = $wpdb->get_var(
164	$wpdb->prepare( 'SELECT GET_LOCK( SHA1( %s ),%d )', $lock_key, $timeout )
165
166	);
167
168	if ( false === $acquired ) {
169	// Only log errors, a failure to acquire lock is not an error.
170	$log_data = [
171	'message' => 'Error while trying to acquire lock.',
172	'key' => $lock_key,
173	'error' => $wpdb->last_error
174	];
175	do_action( 'tribe_log', 'error', __CLASS__, $log_data );
176
177	return false;
178	}
179
180	return true;
181	}
182
183	/**
184	* Tries to acquire the lock using SQL queries.
185	*
186	* This kind of lock does not support timeout to avoid sieging the MySQL server during processes
187	* that are most likely already stressing it. Either the lock is available the moment it's required or not.
188	* The method leverages `INSERT IGNORE` that it's available on MySQL 5.6 and is atomic provided one of the values
189	* we're trying to insert is UNIQUE or PRIMARY: `option_name` is UNIQUE in the `options` table.
190	*
191	* @since 4.12.6
192	*
193	* @param string $lock_key The lock key to try and acquire the lock for.
194	*
195	* @return bool Whether the lock was acquired or not.
196	*/
197	protected function acquire_db_lock_w_queries( $lock_key ) {
198	global $wpdb;
199	$option_name = $this->get_db_lock_option_name( $lock_key );
200	$lock_time = microtime( true );
201
202	//phpcs:disable
203	$rows_affected = $wpdb->query(
204	$wpdb->prepare( "INSERT IGNORE INTO {$wpdb->options}
205	(option_name, option_value, autoload)
206	VALUES
207	(%s, %s, 'no')",
208	$option_name,
209	$lock_time
210	)
211	);
212	//phpcs:enable
213
214	if ( false === $rows_affected ) {
215	$log_data = [
216	'message' => 'Error while trying to acquire lock with database.',
217	'key' => $lock_key,
218	'option_name' => $option_name,
219	'error' => $wpdb->last_error,
220	];
221	do_action( 'tribe_log', 'error', __CLASS__, $log_data );
222
223	return false;
224	}
225
226	/*
227	* The `wpdb::query()` method will return the number of affected rows when using `INSERT`.
228	* 1 row affected means we could INSERT and have the lock, 0 rows affected means we could not INSERT
229	* and have not the lock.
230	*/
231
232	if ( $rows_affected ) {
233	self::$held_db_locks[ $lock_key ] = $lock_time;
234	}
235
236	return (bool) $rows_affected;
237	}
238
239	/**
240	* Returns the option name used to manage the lock for a key in the options table.
241	*
242	* @since 4.12.6
243	*
244	* @param string $lock_key The lock key to build the option name for.
245	*
246	* @return string The name of the option that will be used to manage the lock for the specified key in the
247	* options table.
248	*/
249	public function get_db_lock_option_name( $lock_key ) {
250	return self::$db_lock_option_prefix . $lock_key;
251	}
252
253	/**
254	* Releases the database lock of the record.
255	*
256	* Release a not held db lock will return `null`, not `false`.
257	*
258	* @since 4.12.6
259	*
260	* @param string $lock_key The name of the lock to release.
261	*
262	* @return bool Whether the lock was correctly released or not.
263	*/
264	public function release_db_lock( $lock_key ) {
265	if ( $this->manage_db_lock_w_mysql_functions() ) {
266	return $this->release_db_lock_w_mysql_functions( $lock_key );
267	}
268
269	return $this->release_db_lock_w_queries( $lock_key );
270	}
271
272	/**
273	* Releases a DB lock held by the current database session (`$wpdb` instance) by
274	* using the MySQL `RELEASE_LOCK` function.
275	*
276	* @since 4.12.6
277	*
278	* @param string $lock_key The lock key to release the lock for.
279	*
280	* @return bool Whether the lock was correctly released or not.
281	*/
282	protected function release_db_lock_w_mysql_functions( $lock_key ) {
283	global $wpdb;
284
285	$released = $wpdb->query(
286	$wpdb->prepare( "SELECT RELEASE_LOCK( SHA1( %s ) )", $lock_key )
287	);
288
289	if ( false === $released ) {
290	$log_data = [
291	'message' => 'Error while trying to release lock.',
292	'key' => $lock_key,
293	'error' => $wpdb->last_error
294	];
295	do_action( 'tribe_log', 'error', __CLASS__, $log_data );
296
297	return false;
298	}
299
300	return true;
301	}
302
303	/**
304	* Releases a lock using SQL queries.
305	*
306	* Note: differently from the `release_db_lock_w_mysql_functions`, this method will release the lock
307	* even if the current session is not the one holding the lock.
308	* To protect from this the trait uses a map of registered locks and when the locks where registered.
309	*
310	* @since 4.12.6
311	*
312	* @param string $lock_key The lock key to release the lock for.
313	*
314	* @return bool Whether the lock was released or not, errors will be logged, a `false` value is returned if
315	* the lock was not held to begin with.
316	*/
317	protected function release_db_lock_w_queries( $lock_key ) {
318	if ( ! isset( self::$held_db_locks[ $lock_key ] ) ) {
319	// Avoid sessions that do nothold the lock to release it.
320	return false;
321	}
322
323	global $wpdb;
324	$option_name = $this->get_db_lock_option_name( $lock_key );
325	//phpcs:disable
326	$rows_affected = $wpdb->delete(
327	$wpdb->options,
328	[ 'option_name' => $option_name ],
329	[ '%s' ]
330	);
331	//phpcs:enable
332
333	if ( false === $rows_affected ) {
334	$log_data = [
335	'message' => 'Error while trying to release lock with database.',
336	'key' => $lock_key,
337	'option_name' => $option_name,
338	'error' => $wpdb->last_error,
339	];
340	do_action( 'tribe_log', 'error', __CLASS__, $log_data );
341
342	return false;
343	}
344
345	if ( $rows_affected ) {
346	// Lock successfully released.
347	unset( self::$held_db_locks[ $lock_key ] );
348	}
349
350	return (bool) $rows_affected;
351	}
352	}
353