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This library helps executing critical code in concurrent situations.
php-lock/lock follows semantic versioning. Read more on semver.org.
- PHP 7.1 or above
- Optionally nrk/predis to use the Predis locks.
- Optionally the php-pcntl extension to enable locking with
flock()without busy waiting in CLI scripts. - Optionally
flock(),ext-redis,ext-pdo_mysql,ext-pdo_sqlite,ext-pdo_pgsqlorext-memcachedcan be used as a backend for locks. See examples below. - If
ext-redisis used for locking and is configured to use igbinary for serialization or lzf for compression, additionallyext-igbinaryand/orext-lzfhave to be installed.
To use this library through composer, run the following terminal command inside your repository's root folder.
composer require "malkusch/lock"This library uses the namespace malkusch\lock.
The malkusch\lock\mutex\Mutex class is an abstract class and provides the
base API for this library.
malkusch\lock\mutex\Mutex::synchronized() 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:
$newBalance = $mutex->synchronized(function () use (
$bankAccount,
$amount
): int {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException('You have no credit.');
}
$bankAccount->setBalance($balance);
return$balance;
});malkusch\lock\mutex\Mutex::check() sets a callable, which will be
executed when malkusch\lock\util\DoubleCheckedLocking::then() 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 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() 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() 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:
$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) {
thrownew \DomainException('You have no credit.');
}
}Mutex implementations based on malkush\lock\mutex\LockMutex will throw
malkusch\lock\exception\LockReleaseException 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:
try {
// or $mutex->check(...)$result = $mutex->synchronized(function () {
if (someCondition()) {
thrownew \DomainException();
}
return"result";
});
} catch (LockReleaseException$unlockException) {
if ($unlockException->getCodeException() !== null) {
$codeException = $unlockException->getCodeException()
// do something with the code exception
} else {
$code_result = $unlockException->getCodeResult();
// do something with the code result
}
// deal with LockReleaseException or propagate itthrow$unlockException;
}Because the malkusch\lock\mutex\Mutex class is an abstract class,
you can choose from one of the provided implementations or create/extend your
own implementation.
CASMutexFlockMutexMemcachedMutexPHPRedisMutexPredisMutexSemaphoreMutexTransactionalMutexMySQLMutexPgAdvisoryLockMutex
The CASMutex has to be used with a Compare-and-swap 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().
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:
$mutex = newCASMutex();
$mutex->synchronized(function () use ($memcached, $mutex, $amount): void {
$balance = $memcached->get("balance", null, $casToken);
$balance -= $amount;
if (!$memcached->cas($casToken, "balance", $balance)) {
return;
}
$mutex->notify();
});The FlockMutex is a lock implementation based on
flock().
Example:
$mutex = newFlockMutex(fopen(__FILE__, "r"));
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \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.
The MemcachedMutex is a spinlock implementation which uses the
Memcached API.
Example:
$memcache = new \Memcached();
$memcache->addServer("localhost", 11211);
$mutex = newMemcachedMutex("balance", $memcache);
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException("You have no credit.");
}
$bankAccount->setBalance($balance);
});The PHPRedisMutex is the distributed lock implementation of
RedLock which uses the
phpredis extension.
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:
$redis = newRedis();
$redis->connect("localhost");
$mutex = newPHPRedisMutex([$redis], "balance");
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException("You have no credit.");
}
$bankAccount->setBalance($balance);
});The PredisMutex is the distributed lock implementation of
RedLock which uses the
Predis API.
Example:
$redis = newClient("redis://localhost");
$mutex = newPredisMutex([$redis], "balance");
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException("You have no credit.");
}
$bankAccount->setBalance($balance);
});The SemaphoreMutex is a lock implementation based on Semaphore.
Example:
$semaphore = sem_get(ftok(__FILE__, "a"));
$mutex = newSemaphoreMutex($semaphore);
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException("You have no credit.");
}
$bankAccount->setBalance($balance);
});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:
$mutex = newTransactionalMutex($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) {
thrownew \DomainException("You have no credit.");
}
$pdo->prepare("UPDATE account SET balance = ? WHERE id = ?")
->execute([$balance, $accountId]);
});The MySQLMutex uses MySQL's
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.
$pdo = newPDO("mysql:host=localhost;dbname=test", "username");
$mutex = newMySQLMutex($pdo, "balance", 15);
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException("You have no credit.");
}
$bankAccount->setBalance($balance);
});The PgAdvisoryLockMutex uses PostgreSQL's advisory locking 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.
$pdo = newPDO("pgsql:host=localhost;dbname=test;", "username");
$mutex = newPgAdvisoryLockMutex($pdo, "balance");
$mutex->synchronized(function () use ($bankAccount, $amount) {
$balance = $bankAccount->getBalance();
$balance -= $amount;
if ($balance < 0) {
thrownew \DomainException("You have no credit.");
}
$bankAccount->setBalance($balance);
});This project is free and under the WTFPL. Responsible for this project is Willem Stuursma-Ruwen willem@stuursma.name.
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