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https://github.com/php-lock/lock

Lock library to provide serialized execution of PHP code.
https://github.com/php-lock/lock

lock mutex semaphore

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Lock library to provide serialized execution of PHP code.

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README 

        
**[Requirements](#requirements)** |

**[Installation](#installation)** |

**[Usage](#usage)** |

**[License and authors](#license-and-authors)** |

**[Donations](#donations)**



# php-lock/lock



[![Latest Stable Version](https://poser.pugx.org/malkusch/lock/version)](https://packagist.org/packages/malkusch/lock)

[![Total Downloads](https://poser.pugx.org/malkusch/lock/downloads)](https://packagist.org/packages/malkusch/lock)

[![Latest Unstable Version](https://poser.pugx.org/malkusch/lock/v/unstable)](//packagist.org/packages/malkusch/lock)

[![Build Status](https://travis-ci.org/php-lock/lock.svg?branch=master)](https://travis-ci.org/php-lock/lock)

[![License](https://poser.pugx.org/malkusch/lock/license)](https://packagist.org/packages/malkusch/lock)



This library helps executing critical code in concurrent situations.



php-lock/lock follows semantic versioning. Read more on [semver.org][1].



----



## Requirements



 - PHP 7.1 or above

 - Optionally [nrk/predis][2] to use the Predis locks.

 - Optionally the [php-pcntl][3] extension to enable locking with `flock()`

   without busy waiting in CLI scripts.

 - Optionally `flock()`, `ext-redis`, `ext-pdo_mysql`, `ext-pdo_sqlite`,

   `ext-pdo_pgsql` or `ext-memcached` can be used as a backend for locks. See

   examples below.

 - If `ext-redis` is used for locking and is configured to use igbinary for

   serialization or lzf for compression, additionally `ext-igbinary` and/or

   `ext-lzf` have to be installed.



----



## Installation



### Composer



To use this library through [composer][4], run the following terminal command

inside your repository's root folder.



```sh

composer require "malkusch/lock"

```



## Usage



This library uses the namespace `malkusch\lock`.



### Mutex



The [`malkusch\lock\mutex\Mutex`][5] class is an abstract class and provides the

base API for this library.



#### Mutex::synchronized()



[`malkusch\lock\mutex\Mutex::synchronized()`][6] executes code exclusively. This

method guarantees that the code is only executed by one process at once. Other

processes have to wait until the mutex is available. The critical code may throw

an exception, which would release the lock as well.



This method returns whatever is returned to the given callable. The return

value is not checked, thus it is up to the user to decide if for example the

return value `false` or `null` should be seen as a failed action.



Example:



```php

$newBalance = $mutex->synchronized(function () use (

    $bankAccount,

    $amount

): int {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException('You have no credit.');

    }

    $bankAccount->setBalance($balance);



    return $balance;

});

```



#### Mutex::check()



[`malkusch\lock\mutex\Mutex::check()`][7] sets a callable, which will be

executed when [`malkusch\lock\util\DoubleCheckedLocking::then()`][8] is called,

and performs a double-checked locking pattern, where it's return value decides

if the lock needs to be acquired and the synchronized code to be executed.



See [https://en.wikipedia.org/wiki/Double-checked_locking][9] for a more

detailed explanation of that feature.



If the check's callable returns `false`, no lock will be acquired and the

synchronized code will not be executed. In this case the

[`malkusch\lock\util\DoubleCheckedLocking::then()`][8] method, will also return

`false` to indicate that the check did not pass either before or after acquiring

the lock.



In the case where the check's callable returns a value other than `false`, the

[`malkusch\lock\util\DoubleCheckedLocking::then()`][8] method, will

try to acquire the lock and on success will perform the check again. Only when

the check returns something other than `false` a second time, the synchronized

code callable, which has been passed to `then()` will be executed. In this case

the return value of `then()` will be what ever the given callable returns and

thus up to the user to return `false` or `null` to indicate a failed action as

this return value will not be checked by the library.



Example:



```php

$newBalance = $mutex->check(function () use ($bankAccount, $amount): bool {

    return $bankAccount->getBalance() >= $amount;

})->then(function () use ($bankAccount, $amount): int {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    $bankAccount->setBalance($balance);



    return $balance;

});



if (false === $newBalance) {

    if ($balance < 0) {

        throw new \DomainException('You have no credit.');

    }

}

```



### Extracting code result after lock release exception



Mutex implementations based on [`malkush\lock\mutex\LockMutex`][12] will throw

[`malkusch\lock\exception\LockReleaseException`][13] in case of lock release

problem, but the synchronized code block will be already executed at this point.

In order to read the code result (or an exception thrown there),

`LockReleaseException` provides methods to extract it.



Example:

```php

try {

    // or $mutex->check(...)

    $result = $mutex->synchronized(function () {

        if (someCondition()) {

            throw new \DomainException();

        }



        return "result";

    });

} catch (LockReleaseException $unlockException) {

    if ($unlockException->getCodeException() !== null) {

        $codeException = $unlockException->getCodeException()

        // do something with the code exception

    } else {

        $code_result = $unlockException->getCodeResult();

        // do something with the code result

    }



    // deal with LockReleaseException or propagate it

    throw $unlockException;

}

```



### Implementations



Because the [`malkusch\lock\mutex\Mutex`](#mutex) class is an abstract class,

you can choose from one of the provided implementations or create/extend your

own implementation.



- [`CASMutex`](#casmutex)

- [`FlockMutex`](#flockmutex)

- [`MemcachedMutex`](#memcachedmutex)

- [`PHPRedisMutex`](#phpredismutex)

- [`PredisMutex`](#predismutex)

- [`SemaphoreMutex`](#semaphoremutex)

- [`TransactionalMutex`](#transactionalmutex)

- [`MySQLMutex`](#mysqlmutex)

- [`PgAdvisoryLockMutex`](#pgadvisorylockmutex)



#### CASMutex



The **CASMutex** has to be used with a [Compare-and-swap][10] operation. This

mutex is lock free. It will repeat executing the code until the CAS operation

was successful. The code should therefore notify the mutex by calling

[`malkusch\lock\mutex\CASMutex::notify()`][11].



As the mutex keeps executing the critical code, it must not have any side

effects as long as the CAS operation was not successful.



Example:



```php

$mutex = new CASMutex();

$mutex->synchronized(function () use ($memcached, $mutex, $amount): void {

    $balance = $memcached->get("balance", null, $casToken);

    $balance -= $amount;

    if (!$memcached->cas($casToken, "balance", $balance)) {

        return;

    }

    $mutex->notify();

});

```



#### FlockMutex



The **FlockMutex** is a lock implementation based on

[`flock()`](http://php.net/manual/en/function.flock.php).



Example:

```php

$mutex = new FlockMutex(fopen(__FILE__, "r"));

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



Timeouts are supported as an optional second argument. This uses the `ext-pcntl`

extension if possible or busy waiting if not.



#### MemcachedMutex



The **MemcachedMutex** is a spinlock implementation which uses the

[`Memcached` API](http://php.net/manual/en/book.memcached.php).



Example:

```php

$memcache = new \Memcached();

$memcache->addServer("localhost", 11211);



$mutex = new MemcachedMutex("balance", $memcache);

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



#### PHPRedisMutex



The **PHPRedisMutex** is the distributed lock implementation of

[RedLock](http://redis.io/topics/distlock) which uses the

[`phpredis` extension](https://github.com/phpredis/phpredis).



This implementation requires at least `phpredis-2.2.4`.



If used with a cluster of Redis servers, acquiring and releasing locks will

continue to function as long as a majority of the servers still works.



Example:

```php

$redis = new Redis();

$redis->connect("localhost");



$mutex = new PHPRedisMutex([$redis], "balance");

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



#### PredisMutex



The **PredisMutex** is the distributed lock implementation of

[RedLock](http://redis.io/topics/distlock) which uses the

[`Predis` API](https://github.com/nrk/predis).



Example:

```php

$redis = new Client("redis://localhost");



$mutex = new PredisMutex([$redis], "balance");

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



#### SemaphoreMutex



The **SemaphoreMutex** is a lock implementation based on

[Semaphore](http://php.net/manual/en/ref.sem.php).



Example:

```php

$semaphore = sem_get(ftok(__FILE__, "a"));

$mutex = new SemaphoreMutex($semaphore);

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



#### TransactionalMutex



The **TransactionalMutex**

delegates the serialization to the DBS. The exclusive code is executed within

a transaction. It's up to you to set the correct transaction isolation level.

However if the transaction fails (i.e. a `PDOException` was thrown), the code

will be executed again in a new transaction. Therefore the code must not have

any side effects besides SQL statements. Also the isolation level should be

conserved for the repeated transaction. If the code throws an exception,

the transaction is rolled back and not replayed again.



Example:

```php

$mutex = new TransactionalMutex($pdo);

$mutex->synchronized(function () use ($pdo, $accountId, $amount) {

    $select = $pdo->prepare(

        "SELECT balance FROM account WHERE id = ? FOR UPDATE"

    );

    $select->execute([$accountId]);

    $balance = $select->fetchColumn();



    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $pdo->prepare("UPDATE account SET balance = ? WHERE id = ?")

        ->execute([$balance, $accountId]);

});

```



#### MySQLMutex



The **MySQLMutex** uses MySQL's

[`GET_LOCK`](https://dev.mysql.com/doc/refman/8.0/en/miscellaneous-functions.html#function_get-lock)

function.



It supports time outs. If the connection to the database server is lost or

interrupted, the lock is automatically released.



Note that before MySQL 5.7.5 you cannot use nested locks, any new lock will

silently release already held locks. You should probably refrain from using this

mutex on MySQL versions < 5.7.5.



```php

$pdo = new PDO("mysql:host=localhost;dbname=test", "username");



$mutex = new MySQLMutex($pdo, "balance", 15);

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



#### PgAdvisoryLockMutex



The **PgAdvisoryLockMutex** uses PostgreSQL's

[advisory locking](https://www.postgresql.org/docs/9.4/static/functions-admin.html#FUNCTIONS-ADVISORY-LOCKS)

functions.



Named locks are offered. PostgreSQL locking functions require integers but the

conversion is handled automatically.



No time outs are supported. If the connection to the database server is lost or

interrupted, the lock is automatically released.



```php

$pdo = new PDO("pgsql:host=localhost;dbname=test;", "username");



$mutex = new PgAdvisoryLockMutex($pdo, "balance");

$mutex->synchronized(function () use ($bankAccount, $amount) {

    $balance = $bankAccount->getBalance();

    $balance -= $amount;

    if ($balance < 0) {

        throw new \DomainException("You have no credit.");

    }

    $bankAccount->setBalance($balance);

});

```



## License and authors



This project is free and under the WTFPL.

Responsible for this project is Willem Stuursma-Ruwen .



## Donations



If you like this project and feel generous donate a few Bitcoins here:

[1P5FAZ4QhXCuwYPnLZdk3PJsqePbu1UDDA](bitcoin:1P5FAZ4QhXCuwYPnLZdk3PJsqePbu1UDDA)



[1]: http://semver.org

[2]: https://github.com/nrk/predis

[3]: http://php.net/manual/en/book.pcntl.php

[4]: https://getcomposer.org

[5]: https://github.com/php-lock/lock/blob/master/classes/mutex/Mutex.php

[6]: https://github.com/php-lock/lock/blob/master/classes/mutex/Mutex.php#L38

[7]: https://github.com/php-lock/lock/blob/master/classes/mutex/Mutex.php#L57

[8]: https://github.com/php-lock/lock/blob/master/classes/util/DoubleCheckedLocking.php#L72

[9]: https://en.wikipedia.org/wiki/Double-checked_locking

[10]: https://en.wikipedia.org/wiki/Compare-and-swap

[11]: https://github.com/php-lock/lock/blob/master/classes/mutex/CASMutex.php#L44

[12]: https://github.com/php-lock/lock/blob/master/classes/mutex/LockMutex.php

[13]: https://github.com/php-lock/lock/blob/master/classes/exception/LockReleaseException.php