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115 lines
3.7 KiB
115 lines
3.7 KiB
<?php
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namespace JobLock;
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use DateTime;
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use Doctrine\ORM\EntityManager;
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/**
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* Simple service that persist lock information into database. Used when application with multiple
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* instances needs to run a job or some other procedure only once and avoid other instances spawning
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* concurrent processes.
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*
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* @author Jan Pavlíček <jan@pavlicek.dev>
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*/
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class JobLockService
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{
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// determines default expiration date for locks - after this date, locks are not considered valid even if not released
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const MAXIMUM_LOCK_DURATION = '23 hours 50 minutes';
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// determines how long are expired locks left in the database
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const MAXIMUM_LOCK_LIFETIME = '3 days';
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// determines minimum sleep duration when the job is invoked - used to avoid running the job multiple times
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// from different containers, along with WAIT_MS_MAX - a value is assigned randomly between those two boundaries
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// to create artifical inacurracy and give enough time for locks to be created in other processes
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const WAIT_MS_MIN = 0;
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// upper boundry, same as WAIT_MS_MIN but it is also used as a timeout between job finish and lock release
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const WAIT_MS_MAX = 20000;
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protected EntityManager $em;
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public function __construct(EntityManager $em)
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{
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$this->em = $em;
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}
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/**
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* Create a lock for a job with identifier. If the job is already locked, throw an exception.
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* Uses a random short sleep duration to avoid concurrent runs not seeing each others locks.
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*
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* @throws Common\JobLock\JobLockedException
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*/
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public function acquireLock(string $identifier) : void
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{
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// random sleep is used to avoid too much accuracy which can lead to other instance starting
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// the job while the lock is being created
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usleep(rand(self::WAIT_MS_MIN * 1000, self::WAIT_MS_MAX * 1000));
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// check for current locks that have not expired yet
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$current_lock = $this->em->createQuery('SELECT l FROM ' . JobLock::class . ' l
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WHERE l.identifier = :identifier
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AND l.expires > CURRENT_DATE()
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AND l.released IS NULL')
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->setParameter('identifier', $identifier)
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->getResult();
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if ($current_lock) {
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throw new JobLockedException;
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}
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// persist the new lock
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$lock = new JobLock;
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$lock->setIdentifier($identifier);
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$lock->setExpires(new DateTime('+' . self::MAXIMUM_LOCK_DURATION));
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$lock->setAcquired(new DateTime);
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$this->em->persist($lock);
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$this->em->flush();
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}
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/**
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* find all unreleased locks for given identifier and release them
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*/
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public function releaseLock(string $identifier) : void
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{
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// sleep for maximum amount before releasing the lock to avoid another process with higher
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// wait time to start after the lock is released
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usleep(self::WAIT_MS_MAX * 1000);
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$locks = $this->em->getRepository(JobLock::class)->findBy(['identifier' => $identifier, 'released' => null]);
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$now = new DateTime;
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foreach ($locks as $lock) {
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$lock->setReleased($now);
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}
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$this->em->flush();
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$this->cleanupExpiredLocks();
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}
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/**
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* Removes all locks that have expiration date further in the past than the maximum lock lifetime
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* config constant from the database
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*/
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public function cleanupExpiredLocks() : void
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{
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$threshold = new DateTime('-' . self::MAXIMUM_LOCK_LIFETIME);
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$this->em->createQueryBuilder()
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->delete(JobLock::class, 'l')
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->where('l.expires <= :threshold')
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->setParameter('threshold', $threshold)
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->getQuery()
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->execute();
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}
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}
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