RedLock::checkQuorum() - Code Metrics - Inspection of "Merge pull request #1 from remi-san/quorum" - remi-san/lock - Measure and Improve Code Quality continuously with Scrutinizer

Completed

Push — master ( 5c076b...c6f8b5 )

by Rémi

created 2016-08-30 18:34 UTC

RedLock::checkQuorum() A

↳ Parent: RedLock

Complexity

Conditions	2
Paths	2

Size

Total Lines	6
Code Lines	3

Duplication

Lines	0
Ratio	0 %

Code Coverage

Tests	4
CRAP Score	2

Importance

Changes	1
Bugs	0	Features	1

Metric	Value
c	1
b	0
f	1
dl	0
loc	6
ccs	4
cts	4
cp	1
rs	9.4285
cc	2
eloc	3
nc	2
nop	1
crap	2

<?php

namespace RemiSan\Lock\Implementations;

use RemiSan\Lock\Exceptions\LockingException;
use RemiSan\Lock\Exceptions\UnlockingException;
use RemiSan\Lock\Lock;
use RemiSan\Lock\Locker;
use RemiSan\Lock\TokenGenerator;
use Symfony\Component\Stopwatch\Stopwatch;

final class RedLock implements Locker
{
    /** @var float */
    const CLOCK_DRIFT_FACTOR = 0.01;

    /** @var \Redis[] */
    private $instances = [];

    /** @var TokenGenerator */
    private $tokenGenerator;

    /** @var Stopwatch */
    private $stopwatch;

    /** @var int */
    private $quorum;

    /**
     * @param \Redis[]       $instances      Array of pre-connected \Redis objects
     * @param TokenGenerator $tokenGenerator The token generator
     * @param Stopwatch      $stopwatch      A way to measure time passed
     */
    public function __construct(
        array $instances,
        TokenGenerator $tokenGenerator,
        Stopwatch $stopwatch
    ) {
        $this->setInstances($instances);
        $this->setQuorum();

        $this->tokenGenerator = $tokenGenerator;
        $this->stopwatch = $stopwatch;
    }

    /**
     * {@inheritdoc}
     */
    public function lock($resource, $ttl = null, $retryDelay = 0, $retryCount = 0)
    {
        $lock = new Lock($resource, $this->tokenGenerator->generateToken());

        $tried = 0;
        while (true) {
            try {
                return $this->monitoredLockingOfAllInstances($lock, $ttl);
            } catch (LockingException $e) {
                $this->resetLock($lock);
            }

            if ($tried++ === $retryCount) {
                break;
            }

            $this->waitBeforeRetrying($retryDelay);
        }

        throw new LockingException();
    }

    /**
     * {@inheritdoc}
     */
    public function isResourceLocked($resource)
    {
        foreach ($this->instances as $instance) {
            if ($this->isInstanceResourceLocked($instance, $resource)) {
                return true;
            }
        }

        return false;
    }

    /**
     * {@inheritdoc}
     */
    public function unlock(Lock $lock)
    {
        foreach ($this->instances as $instance) {
            if (!$this->unlockInstance($instance, $lock)) {
                if ($this->isInstanceResourceLocked($instance, $lock->getResource())) {
                    throw new UnlockingException(); // Only throw an exception if the lock is still present
                }
            }
        }
    }

    /**
     * @param Lock $lock
     * @param int  $ttl
     *
     * @throws LockingException
     *
     * @return Lock
     */
    private function monitoredLockingOfAllInstances(Lock $lock, $ttl)
    {
        $timeMeasure = $this->stopwatch->start($lock->getToken());
        $instancesLocked = $this->lockInstances($lock, $ttl);
        $timeMeasure->stop();

        $this->checkQuorum($instancesLocked);

        if ($ttl) {
            self::checkTtl($timeMeasure->getDuration(), $ttl);
            $lock->setValidityTimeEnd($timeMeasure->getOrigin() + $ttl);
        }

        return $lock;
    }

    /**
     * @param Lock $lock
     * @param int  $ttl
     *
     * @return int The number of instances locked
     */
    private function lockInstances(Lock $lock, $ttl)
    {
        $instancesLocked = 0;

        foreach ($this->instances as $instance) {
            if ($this->lockInstance($instance, $lock, $ttl)) {
                ++$instancesLocked;
            }
        }

        return $instancesLocked;
    }

    /**
     * @param \Redis $instance Server instance to be locked
     * @param Lock   $lock     The lock instance
     * @param int    $ttl      Time to live in milliseconds
     *
     * @return bool
     */
    private function lockInstance(\Redis $instance, Lock $lock, $ttl)
    {
        $options = ['NX'];

        if ($ttl) {
            $options['PX'] = (int) $ttl;
        }

        return (bool) $instance->set($lock->getResource(), (string) $lock->getToken(), $options);
    }

    /**
     * @param Lock $lock
     */
    private function resetLock($lock)
    {
        foreach ($this->instances as $instance) {
            $this->unlockInstance($instance, $lock);
        }
    }

    /**
     * @param \Redis $instance
     * @param string $resource
     *
     * @return bool
     */
    private function isInstanceResourceLocked(\Redis $instance, $resource)
    {
        return (bool) $instance->exists($resource);
    }

    /**
     * @param \Redis $instance Server instance to be unlocked
     * @param Lock   $lock     The lock to unlock
     *
     * @return bool
     */
    private function unlockInstance(\Redis $instance, Lock $lock)
    {
        $script = '
            if redis.call("GET", KEYS[1]) == ARGV[1] then
                return redis.call("DEL", KEYS[1])
            else
                return 0
            end
        ';

        return (bool) $instance->evaluate(
            $script,
            [$lock->getResource(), (string) $lock->getToken()],
            1
        );
    }

    /**
     * @param \Redis[] $instances
     *
     * @throws \Exception
     */
    private function setInstances(array $instances)
    {
        if (count($instances) === 0) {
            throw new \InvalidArgumentException('You must provide at least one Redis instance.');
        }

        foreach ($instances as $instance) {
            if (!$instance->isConnected()) {
                throw new \InvalidArgumentException('The Redis must be connected.');
            }
        }

        $this->instances = $instances;
    }

    private function setQuorum()
    {
        $numberOfRedisInstances = count($this->instances);
        $this->quorum = (int) round(min($numberOfRedisInstances, ($numberOfRedisInstances / 2) + 1));
    }

    /**
     * @param int $instancesLocked
     *
     * @throws LockingException
     */
    private function checkQuorum($instancesLocked)
    {
        if ($instancesLocked < $this->quorum) {
            throw new LockingException();
        }
    }

    /**
     * @param int $retryDelay
     */
    private function waitBeforeRetrying($retryDelay)
    {
        usleep($retryDelay * 1000);
    }

    /**
     * @param int $elapsedTime
     * @param int $ttl
     *
     * @throws LockingException
     */
    private static function checkTtl($elapsedTime, $ttl)
    {
        $adjustedElapsedTime = ($elapsedTime + self::getDrift($ttl));

        if ($adjustedElapsedTime >= $ttl) {
            throw new LockingException();
        }
    }

    /**
     * Get the drift time based on ttl in ms.
     *
     * @param int $ttl
     *
     * @return float
     */
    private static function getDrift($ttl)
    {
        // Add 2 milliseconds to the drift to account for Redis expires
        // precision, which is 1 millisecond, plus 2 millisecond min drift
        // for small TTLs.

        $redisExpiresPrecision = 2;
        $minDrift = ($ttl) ? ceil($ttl * self::CLOCK_DRIFT_FACTOR) : 0;

        return $minDrift + $redisExpiresPrecision;
    }
}


1		<?php
2
3		namespace RemiSan\Lock\Implementations;
4
5		use RemiSan\Lock\Exceptions\LockingException;
6		use RemiSan\Lock\Exceptions\UnlockingException;
7		use RemiSan\Lock\Lock;
8		use RemiSan\Lock\Locker;
9		use RemiSan\Lock\TokenGenerator;
10		use Symfony\Component\Stopwatch\Stopwatch;
11
12		final class RedLock implements Locker
13		{
14		/** @var float */
15		const CLOCK_DRIFT_FACTOR = 0.01;
16
17		/** @var \Redis[] */
18		private $instances = [];
19
20		/** @var TokenGenerator */
21		private $tokenGenerator;
22
23		/** @var Stopwatch */
24		private $stopwatch;
25
26		/** @var int */
27		private $quorum;
28
29		/**
30		* @param \Redis[] $instances Array of pre-connected \Redis objects
31		* @param TokenGenerator $tokenGenerator The token generator
32		* @param Stopwatch $stopwatch A way to measure time passed
33		*/
34	39	public function __construct(
35		array $instances,
36		TokenGenerator $tokenGenerator,
37		Stopwatch $stopwatch
38		) {
39	39	$this->setInstances($instances);
40	39	$this->setQuorum();
41
42	39	$this->tokenGenerator = $tokenGenerator;
43	39	$this->stopwatch = $stopwatch;
44	39	}
45
46		/**
47		* {@inheritdoc}
48		*/
49	12	public function lock($resource, $ttl = null, $retryDelay = 0, $retryCount = 0)
50		{
51	12	$lock = new Lock($resource, $this->tokenGenerator->generateToken());
52
53	12	$tried = 0;
54	12	while (true) {
55		try {
56	12	return $this->monitoredLockingOfAllInstances($lock, $ttl);
57	6	} catch (LockingException $e) {
58	6	$this->resetLock($lock);
59		}
60
61	6	if ($tried++ === $retryCount) {
62	6	break;
63		}
64
65	6	$this->waitBeforeRetrying($retryDelay);
66	4	}
67
68	6	throw new LockingException();
69		}
70
71		/**
72		* {@inheritdoc}
73		*/
74	9	public function isResourceLocked($resource)
75		{
76	9	foreach ($this->instances as $instance) {
77	9	if ($this->isInstanceResourceLocked($instance, $resource)) {
78	7	return true;
79		}
80	4	}
81
82	3	return false;
83		}
84
85		/**
86		* {@inheritdoc}
87		*/
88	12	public function unlock(Lock $lock)
89		{
90	12	foreach ($this->instances as $instance) {
91	12	if (!$this->unlockInstance($instance, $lock)) {
92	9	if ($this->isInstanceResourceLocked($instance, $lock->getResource())) {
93	8	throw new UnlockingException(); // Only throw an exception if the lock is still present
94		}
95	2	}
96	6	}
97	6	}
98
99		/**
100		* @param Lock $lock
101		* @param int $ttl
102		*
103		* @throws LockingException
104		*
105		* @return Lock
106		*/
107	12	private function monitoredLockingOfAllInstances(Lock $lock, $ttl)
108		{
109	12	$timeMeasure = $this->stopwatch->start($lock->getToken());
110	12	$instancesLocked = $this->lockInstances($lock, $ttl);
111	12	$timeMeasure->stop();
112
113	12	$this->checkQuorum($instancesLocked);
114
115	9	if ($ttl) {
116	6	self::checkTtl($timeMeasure->getDuration(), $ttl);
117	3	$lock->setValidityTimeEnd($timeMeasure->getOrigin() + $ttl);
118	2	}
119
120	6	return $lock;
121		}
122
123		/**
124		* @param Lock $lock
125		* @param int $ttl
126		*
127		* @return int The number of instances locked
128		*/
129	12	private function lockInstances(Lock $lock, $ttl)
130		{
131	12	$instancesLocked = 0;
132
133	12	foreach ($this->instances as $instance) {
134	12	if ($this->lockInstance($instance, $lock, $ttl)) {
135	12	++$instancesLocked;
136	8	}
137	8	}
138
139	12	return $instancesLocked;
140		}
141
142		/**
143		* @param \Redis $instance Server instance to be locked
144		* @param Lock $lock The lock instance
145		* @param int $ttl Time to live in milliseconds
146		*
147		* @return bool
148		*/
149	12	private function lockInstance(\Redis $instance, Lock $lock, $ttl)
150		{
151	12	$options = ['NX'];
152
153	12	if ($ttl) {
154	9	$options['PX'] = (int) $ttl;
155	6	}
156
157	12	return (bool) $instance->set($lock->getResource(), (string) $lock->getToken(), $options);
158		}
159
160		/**
161		* @param Lock $lock
162		*/
163	6	private function resetLock($lock)
164		{
165	6	foreach ($this->instances as $instance) {
166	6	$this->unlockInstance($instance, $lock);
167	4	}
168	6	}
169
170		/**
171		* @param \Redis $instance
172		* @param string $resource
173		*
174		* @return bool
175		*/
176	18	private function isInstanceResourceLocked(\Redis $instance, $resource)
177		{
178	18	return (bool) $instance->exists($resource);
179		}
180
181		/**
182		* @param \Redis $instance Server instance to be unlocked
183		* @param Lock $lock The lock to unlock
184		*
185		* @return bool
186		*/
187	18	private function unlockInstance(\Redis $instance, Lock $lock)
188		{
189		$script = '
190		if redis.call("GET", KEYS[1]) == ARGV[1] then
191		return redis.call("DEL", KEYS[1])
192		else
193		return 0
194		end
195	18	';
196
197	18	return (bool) $instance->evaluate(
198	12	$script,
199	18	[$lock->getResource(), (string) $lock->getToken()],
200	6	1
201	12	);
202		}
203
204		/**
205		* @param \Redis[] $instances
206		*
207		* @throws \Exception
208		*/
209	39	private function setInstances(array $instances)
210		{
211	39	if (count($instances) === 0) {
212	3	throw new \InvalidArgumentException('You must provide at least one Redis instance.');
213		}
214
215	39	foreach ($instances as $instance) {
216	39	if (!$instance->isConnected()) {
217	15	throw new \InvalidArgumentException('The Redis must be connected.');
218		}
219	26	}
220
221	39	$this->instances = $instances;
222	39	}
223
224	39	private function setQuorum()
225		{
226	39	$numberOfRedisInstances = count($this->instances);
227	39	$this->quorum = (int) round(min($numberOfRedisInstances, ($numberOfRedisInstances / 2) + 1));
228	39	}
229
230		/**
231		* @param int $instancesLocked
232		*
233		* @throws LockingException
234		*/
235	12	private function checkQuorum($instancesLocked)
236		{
237	12	if ($instancesLocked < $this->quorum) {
238	3	throw new LockingException();
239		}
240	9	}
241
242		/**
243		* @param int $retryDelay
244		*/
245	6	private function waitBeforeRetrying($retryDelay)
246		{
247	6	usleep($retryDelay * 1000);
248	6	}
249
250		/**
251		* @param int $elapsedTime
252		* @param int $ttl
253		*
254		* @throws LockingException
255		*/
256	6	private static function checkTtl($elapsedTime, $ttl)
257		{
258	6	$adjustedElapsedTime = ($elapsedTime + self::getDrift($ttl));
259
260	6	if ($adjustedElapsedTime >= $ttl) {
261	3	throw new LockingException();
262		}
263	3	}
264
265		/**
266		* Get the drift time based on ttl in ms.
267		*
268		* @param int $ttl
269		*
270		* @return float
271		*/
272	6	private static function getDrift($ttl)
273		{
274		// Add 2 milliseconds to the drift to account for Redis expires
275		// precision, which is 1 millisecond, plus 2 millisecond min drift
276		// for small TTLs.
277
278	6	$redisExpiresPrecision = 2;
279	6	$minDrift = ($ttl) ? ceil($ttl * self::CLOCK_DRIFT_FACTOR) : 0;
280
281	6	return $minDrift + $redisExpiresPrecision;
282		}
283		}
284

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RedLock::checkQuorum() A

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