404-solution / includes / stats / StatsRefreshLock.php

StatsRefreshLock.php in 404 Solution trunk, at includes/stats/StatsRefreshLock.php

97 lines 3.7 KB

Raw Download Zip

1	<?php
2
3	if (!defined('ABSPATH')) {
4	exit;
5	}
6
7	/**
8	* Coordinates stats refresh work through WordPress option locks.
9	*/
10	class ABJ_404_Solution_StatsRefreshLock {
11
12	/**
13	* Distributed lock lifetime. This must exceed the longest guarded query
14	* budget (the 60-second high-impact count) so a live worker is never
15	* mistaken for a stale lock while its query is still running.
16	*
17	* @var int
18	*/
19	const REFRESH_LOCK_COOLDOWN_SECONDS = 120;
20
21	/** @var ABJ_404_Solution_DatabaseCoreInterface */
22	private $dbCore;
23
24	/** @var array<string, string> Cache key to exact row value held by this instance. */
25	private $heldValues = array();
26
27	/** @param ABJ_404_Solution_DatabaseCoreInterface $dbCore */
28	public function __construct(ABJ_404_Solution_DatabaseCoreInterface $dbCore) {
29	$this->dbCore = $dbCore;
30	}
31
32	/** @param string $cacheKey @return bool */
33	public function acquire(string $cacheKey): bool {
34	$lockKey = $this->getOptionName($cacheKey);
35	$lockRow = $this->lockRow();
36	$now = abj_clock()->now();
37	$claimValue = ABJ_404_Solution_ExclusiveOptionRow::uniqueClaimValue((string)$now);
38
39	if ($lockRow->claim(array('optionName' => $lockKey, 'value' => $claimValue))) {
40	$this->heldValues[$cacheKey] = $claimValue;
41	return true;
42	}
43
44	// A row already exists. Read it from the table (not from the options
45	// cache, which answers a concurrent request with its own write) and
46	// displace it only when it has genuinely aged out. Both the removal and
47	// the retry are conditional/atomic, so several requests finding the
48	// same expired lock still produce exactly one winner.
49	$lockValue = $lockRow->valueOf($lockKey);
50	if ($lockValue === '') {
51	$claimValue = ABJ_404_Solution_ExclusiveOptionRow::uniqueClaimValue((string)$now);
52	$claimed = $lockRow->claim(array('optionName' => $lockKey, 'value' => $claimValue));
53	if ($claimed) {
54	$this->heldValues[$cacheKey] = $claimValue;
55	}
56	return $claimed;
57	}
58
59	$timestampPart = explode(':', $lockValue, 2)[0];
60	$lockTs = is_numeric($timestampPart) ? (int)$timestampPart : 0;
61	if ($lockTs > 0 && ($now - $lockTs) > self::REFRESH_LOCK_COOLDOWN_SECONDS) {
62	$lockRow->releaseIfValueIs(array('optionName' => $lockKey, 'value' => $lockValue));
63	$claimValue = ABJ_404_Solution_ExclusiveOptionRow::uniqueClaimValue((string)$now);
64	$claimed = $lockRow->claim(array('optionName' => $lockKey, 'value' => $claimValue));
65	if ($claimed) {
66	$this->heldValues[$cacheKey] = $claimValue;
67	}
68	return $claimed;
69	}
70
71	return false;
72	}
73
74	/** @param string $cacheKey @return void */
75	public function release(string $cacheKey): void {
76	if (!isset($this->heldValues[$cacheKey])) {
77	return;
78	}
79	$this->lockRow()->releaseIfValueIs(array(
80	'optionName' => $this->getOptionName($cacheKey),
81	'value' => $this->heldValues[$cacheKey],
82	));
83	unset($this->heldValues[$cacheKey]);
84	}
85
86	/** The lock row itself. Stateless, so a fresh instance costs nothing.
87	* @return ABJ_404_Solution_ExclusiveOptionRow */
88	private function lockRow(): ABJ_404_Solution_ExclusiveOptionRow {
89	return new ABJ_404_Solution_ExclusiveOptionRow();
90	}
91
92	/** @param string $cacheKey @return string */
93	private function getOptionName(string $cacheKey): string {
94	return $this->dbCore->tableNameResolver()->getLowercasePrefix() . 'abj404_view_cache_lock_' . md5((string)$cacheKey);
95	}
96	}
97