decalog / includes / libraries / lock / mutex / CASMutex.php

CASMutex.php in DecaLog 4.4.0, at includes/libraries/lock/mutex/CASMutex.php

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1	<?php
2
3	declare(strict_types=1);
4
5	namespace malkusch\lock\mutex;
6
7	use malkusch\lock\exception\TimeoutException;
8	use malkusch\lock\util\Loop;
9
10	/**
11	* CAS based mutex implementation.
12	*
13	* This mutex doesn't lock at all. It implements the compare-and-swap
14	* approach. I.e. it will repeat executing the code block until it wasn't
15	* modified in between. Use this only when you know that concurrency is
16	* a rare event.
17	*
18	* @author Markus Malkusch <[email protected]>
19	* @link bitcoin:1P5FAZ4QhXCuwYPnLZdk3PJsqePbu1UDDA Donations
20	* @license WTFPL
21	*/
22	class CASMutex extends Mutex
23	{
24	/**
25	* @var Loop The loop.
26	*/
27	private $loop;
28
29	/**
30	* Sets the timeout.
31	*
32	* The default is 3 seconds.
33	*
34	* @param int $timeout The timeout in seconds.
35	* @throws \LengthException The timeout must be greater than 0.
36	*/
37	public function __construct(int $timeout = 3)
38	{
39	$this->loop = new Loop($timeout);
40	}
41
42	/**
43	* Notifies the Mutex about a successful CAS operation.
44	*/
45	public function notify(): void
46	{
47	$this->loop->end();
48	}
49
50	/**
51	* Repeats executing a code until a compare-and-swap operation was successful.
52	*
53	* The code has to be designed in a way that it can be repeated without any
54	* side effects. When the CAS operation was successful it should notify
55	* this mutex by calling {@link CASMutex::notify()}. I.e. the only side effects
56	* of the code may happen after a successful CAS operation. The CAS
57	* operation itself is a valid side effect as well.
58	*
59	* If the code throws an exception it will stop repeating the execution.
60	*
61	* Example:
62	* <code>
63	* $mutex = new CASMutex();
64	* $mutex->synchronized(function () use ($memcached, $mutex, $amount) {
65	* $balance = $memcached->get("balance", null, $casToken);
66	* $balance -= $amount;
67	* if (!$memcached->cas($casToken, "balance", $balance)) {
68	* return;
69	*
70	* }
71	* $mutex->notify();
72	* });
73	* </code>
74	*
75	* @param callable $code The synchronized execution block.
76	* @throws \Exception The execution block threw an exception.
77	* @throws TimeoutException The timeout was reached.
78	* @return mixed The return value of the execution block.
79	*
80	*/
81	public function synchronized(callable $code)
82	{
83	return $this->loop->execute($code);
84	}
85	}
86