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<?php |
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namespace FluentBooking\App\Modules\MCP\Support; |
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|
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defined('ABSPATH') || exit; |
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|
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/** |
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* A short-lived exclusive hold on one slot for one host. |
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* |
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* Checking availability and inserting the booking is a race, and the schema |
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* can't close it: group events seat several bookings in one slot, so there is |
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* no unique index on (event, host, start_time). MCP makes the race likelier |
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* because agents retry and the confirm round-trip adds a human-length pause. |
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* |
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* The lock is an INSERT IGNORE on the unique `option_name` index, so exactly |
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* one concurrent caller wins. GET_LOCK is avoided: some managed hosts disable |
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* it, and it is per-connection, which connection pooling breaks. |
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* |
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* Not a general-purpose lock: the TTL is seconds, a failed acquire returns |
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* instead of waiting, and an expired lock is stolen. |
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* |
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* Only MCP writes take these locks. Bookings from the public page and admin UI |
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* don't, so against those, availability re-checking is still the only guard. |
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* |
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* @since 2.3.0 |
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*/ |
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class SlotLock |
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{ |
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// Covers a slot query plus the insert and its hooks; short enough that a |
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// fatal mid-write frees the slot quickly. |
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const TTL = 15; |
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|
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const PREFIX = 'fcal_mcp_slot_'; |
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|
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// Lock granularity in seconds: the finest slot interval the plugin offers. |
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const BUCKET = 900; |
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|
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// A day of buckets, so a bad end time can't become an unbounded insert loop. |
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const MAX_BUCKETS = 96; |
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|
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/** |
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* Take the lock for one slot, or return false when someone else holds it. |
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* |
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* @param int $eventId |
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* @param string $startTimeUtc 'Y-m-d H:i:s' |
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* @param int|null $hostId null on single-host events |
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* |
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* @return string|false the lock key to pass to release(), or false |
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*/ |
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public static function acquire($eventId, $startTimeUtc, $hostId = null) |
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{ |
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global $wpdb; |
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|
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$key = self::key($eventId, $startTimeUtc, $hostId); |
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$owner = wp_generate_password(20, false, false); |
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|
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// Read the stored bytes, not get_option()'s unserialized (and possibly |
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// cached) copy: the steal below deletes by exact value. |
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$existing = $wpdb->get_var( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"SELECT `option_value` FROM `{$wpdb->options}` WHERE `option_name` = %s", |
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$key |
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) |
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); |
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|
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$record = ($existing === null) ? null : maybe_unserialize($existing); |
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|
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// Steal an expired lock left by a request that died mid-write. Deleting |
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// by the value just read stops a slower racer from deleting the |
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// winner's fresh row. |
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if (is_array($record) && !empty($record['expires']) && $record['expires'] < time()) { |
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$wpdb->query( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"DELETE FROM `{$wpdb->options}` WHERE `option_name` = %s AND `option_value` = %s", |
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$key, |
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$existing |
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) |
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); |
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|
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wp_cache_delete($key, 'options'); |
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} |
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|
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// Same primitive as WP_Upgrader::create_lock. Not add_option(): its ON |
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// DUPLICATE KEY UPDATE reports success even when the row already existed. |
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$inserted = $wpdb->query( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"INSERT IGNORE INTO `{$wpdb->options}` (`option_name`, `option_value`, `autoload`) VALUES (%s, %s, 'no')", |
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$key, |
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maybe_serialize(['expires' => time() + self::TTL, 'owner' => $owner]) |
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) |
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); |
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|
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// The row went in behind the options cache's back. |
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wp_cache_delete($key, 'options'); |
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|
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$notoptions = wp_cache_get('notoptions', 'options'); |
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|
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if (is_array($notoptions) && isset($notoptions[$key])) { |
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unset($notoptions[$key]); |
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wp_cache_set('notoptions', $notoptions, 'options'); |
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} |
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|
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if (!$inserted) { |
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return false; |
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} |
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|
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// The owner in the handle lets release() prove it holds this lock and |
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// not a successor's. |
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return $key . '|' . $owner; |
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} |
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|
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/** |
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* Claim one instant for every host a booking would occupy, all or nothing. |
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* |
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* A collective event books each of its hosts. Partial claims are released |
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* before returning false. |
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* |
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* @param int $eventId |
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* @param string $startTimeUtc |
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* @param array $hostIds |
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* |
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* @return array|false handles to pass to releaseAll(), or false |
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*/ |
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public static function acquireAll($eventId, $startTimeUtc, $hostIds) |
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{ |
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$handles = []; |
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|
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foreach (array_unique(array_map('intval', (array) $hostIds)) as $hostId) { |
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$handle = self::acquire($eventId, $startTimeUtc, $hostId); |
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|
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if (!$handle) { |
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self::releaseAll($handles); |
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|
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return false; |
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} |
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$handles[] = $handle; |
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} |
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|
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return $handles; |
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} |
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|
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/** |
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* Claim every bucket a booking would occupy, for every host it would |
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* occupy, all or nothing. |
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* |
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* Overlapping bookings with different starts (10:00 for 30 min, 10:15 for |
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* 15) always share a bucket, so they collide. Abutting ones don't. |
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* |
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* @param int $eventId |
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* @param string $startTimeUtc 'Y-m-d H:i:s' |
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* @param string $endTimeUtc 'Y-m-d H:i:s' |
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* @param array $hostIds |
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* |
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* @return array|false handles to pass to releaseAll(), or false |
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*/ |
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public static function acquireInterval($eventId, $startTimeUtc, $endTimeUtc, $hostIds) |
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{ |
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$buckets = self::buckets($startTimeUtc, $endTimeUtc); |
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|
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if (!$buckets) { |
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return false; |
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} |
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|
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$handles = []; |
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foreach (array_unique(array_map('intval', (array) $hostIds)) as $hostId) { |
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foreach ($buckets as $bucket) { |
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$handle = self::acquire($eventId, $bucket, $hostId); |
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|
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if (!$handle) { |
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self::releaseAll($handles); |
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return false; |
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} |
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$handles[] = $handle; |
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} |
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} |
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|
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return $handles; |
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} |
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|
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/** |
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* Bucket starts an interval touches. Half open, so a booking ending on a |
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* boundary doesn't claim the next bucket. |
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* |
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* @return array of 'Y-m-d H:i:s' |
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*/ |
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private static function buckets($startTimeUtc, $endTimeUtc) |
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{ |
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$start = strtotime($startTimeUtc . ' UTC'); |
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$end = strtotime($endTimeUtc . ' UTC'); |
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|
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if (!$start) { |
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return []; |
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} |
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if (!$end || $end <= $start) { |
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$end = $start + 1; |
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} |
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|
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$buckets = []; |
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|
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for ($t = $start - ($start % self::BUCKET); $t < $end; $t += self::BUCKET) { |
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$buckets[] = gmdate('Y-m-d H:i:s', $t); // phpcs:ignore WordPress.DateTime.RestrictedFunctions.date_date |
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if (count($buckets) >= self::MAX_BUCKETS) { |
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break; |
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} |
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} |
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|
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return $buckets; |
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} |
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|
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/** |
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* @param array|string|false $handles |
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* |
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* @return bool whether every lease is still held |
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*/ |
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public static function renewAll($handles) |
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{ |
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foreach ((array) $handles as $handle) { |
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if (!self::renew($handle)) { |
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return false; |
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} |
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} |
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|
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return true; |
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} |
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|
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/** |
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* @param array|string|false $handles |
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*/ |
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public static function releaseAll($handles) |
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{ |
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foreach ((array) $handles as $handle) { |
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self::release($handle); |
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} |
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} |
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|
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/** |
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* Re-assert a lease this caller still owns, pushing its expiry out. |
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* |
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* isSpotAvailable() can make a live FreeBusy call per calendar per host, |
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* which on a team event can outlast TTL, and acquire() steals expired |
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* leases. Renewing before the write keeps the lock held. |
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* |
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* Matches the exact stored bytes, so a caller whose lease was stolen gets |
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* false instead of overwriting the new owner. |
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* |
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* @param string|false $handle the value returned by acquire() |
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* |
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* @return bool whether the caller still holds the lock |
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*/ |
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public static function renew($handle) |
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{ |
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global $wpdb; |
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|
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if (!$handle || strpos($handle, '|') === false) { |
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return false; |
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} |
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|
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list($key, $owner) = explode('|', $handle, 2); |
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|
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$existing = $wpdb->get_var( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"SELECT `option_value` FROM `{$wpdb->options}` WHERE `option_name` = %s", |
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$key |
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) |
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); |
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|
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if ($existing === null) { |
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return false; |
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} |
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|
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$record = maybe_unserialize($existing); |
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|
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if (!is_array($record) || !isset($record['owner']) || !hash_equals((string) $record['owner'], $owner)) { |
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return false; |
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} |
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|
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$renewed = maybe_serialize(['expires' => time() + self::TTL, 'owner' => $owner]); |
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|
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$updated = $wpdb->query( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"UPDATE `{$wpdb->options}` SET `option_value` = %s WHERE `option_name` = %s AND `option_value` = %s", |
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$renewed, |
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$key, |
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$existing |
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) |
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); |
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|
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wp_cache_delete($key, 'options'); |
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|
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// MySQL counts changed rows, not matched ones, so a renew within the |
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// same second reports zero even though the row is still ours. |
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return $updated ? true : ($renewed === $existing); |
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} |
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|
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/** |
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* Release a lock this caller actually holds. |
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* |
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* A lease can expire during a slow booking hook and be taken by another |
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* request; a plain delete_option() would then free the successor's lock. |
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* The delete matches the exact value checked, so a lapsed owner's delete |
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* matches nothing. |
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* |
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* @param string|false $handle the value returned by acquire() |
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*/ |
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public static function release($handle) |
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{ |
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global $wpdb; |
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|
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if (!$handle || strpos($handle, '|') === false) { |
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return; |
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} |
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|
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list($key, $owner) = explode('|', $handle, 2); |
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|
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$existing = $wpdb->get_var( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"SELECT `option_value` FROM `{$wpdb->options}` WHERE `option_name` = %s", |
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$key |
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) |
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); |
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|
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if ($existing === null) { |
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return; |
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} |
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|
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$record = maybe_unserialize($existing); |
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|
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if (!is_array($record) || !isset($record['owner']) || !hash_equals((string) $record['owner'], $owner)) { |
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return; |
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} |
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|
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$wpdb->query( // phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching |
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$wpdb->prepare( |
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"DELETE FROM `{$wpdb->options}` WHERE `option_name` = %s AND `option_value` = %s", |
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$key, |
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$existing |
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) |
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); |
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|
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wp_cache_delete($key, 'options'); |
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} |
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|
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/** |
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* Keyed on the host, since the person is the constrained resource: it blocks |
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* one host double-booked via two event types, while two team hosts can |
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* still take the same minute. Round robin has no host until |
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* isSpotAvailable() picks one, so it keys on the event and the caller takes |
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* a host-keyed lock afterwards. |
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* |
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* @return string |
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*/ |
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private static function key($eventId, $startTimeUtc, $hostId) |
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{ |
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$scope = $hostId ? 'h' . (int) $hostId : 'e' . (int) $eventId; |
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|
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return self::PREFIX . md5($scope . '|' . $startTimeUtc); |
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} |
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} |
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|
