rfc:object_scope_prng

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rfc:object_scope_prng [2021/01/17 09:08]
zeriyoshi
rfc:object_scope_prng [2021/04/14 14:38] (current)
zeriyoshi status update
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 ====== PHP RFC: Object scoped RNG Implementations. ====== ====== PHP RFC: Object scoped RNG Implementations. ======
-  * Version: 1.1 +  * Version: 2.1 (Implementation: 1.3) 
-  * Date: 2021-01-17+  * Date: 2020-12-20
   * Author: Go Kudo <zeriyoshi@gmail.com>   * Author: Go Kudo <zeriyoshi@gmail.com>
-  * Status: Under Discussion+  * Status: Declined
   * Implementation: https://github.com/php/php-src/pull/6568   * Implementation: https://github.com/php/php-src/pull/6568
   * First Published at: https://wiki.php.net/rfc/object_scope_prng   * First Published at: https://wiki.php.net/rfc/object_scope_prng
  
 ===== Introduction ===== ===== Introduction =====
 +PHP currently implements an RNG based on the Mersenne Twister, which can be used with mt_srand() and mt_rand().
  
-PHP currently provides the mt_srand() and mt_rand() functions based on the Meresenne Twister as PRNGs+<code php> 
-Howeversince these functions keep their state in global spaceunintended function calls may cause inconsistency even for the same seed value.+\mt_srand(1234); // Seeding internal MT state. 
 +\mt_rand(); // Generate random number
 +</code> 
 + 
 +The shuffle()str_shuffle()and array_rand() functions are also available.
  
 <code php> <code php>
-mt_srand(1234); +$array = [0 => 'foo', 1 => 'bar', 2 => 'baz']; 
-foo(); +\shuffle($array); // Shuffling array using internal MT state. 
-mt_rand() === 411284887; // false+\str_shuffle('foobar'); // Shuffling string using internal MT state. 
 +\array_rand($array, 1); // Randomize array using internal MT state. 
 +</code> 
 + 
 +However, the current implementation of the Mersenne Twister keeps the state in the global scope, which can easily be unrepeatable with additional code. 
 + 
 +<code php> 
 +\mt_srand(1234); 
 +\str_shuffle('foobar'); // Result "afroob", always consistent. 
 + 
 +\mt_srand(1234); 
 +example_of_additional_code(); 
 +\str_shuffle('foobar'); // Result "rfoaob"
  
-function foo() { +function example_of_additional_code() { 
-    mt_rand(); // code added+    \mt_rand(); // Unintended changes in internal MT state!
 } }
 </code> </code>
  
-This is inappropriate for applications that require consistency in the generated values (game logictest code, etc.). +This is fine if you want to get a completely random result, but it is inconsistent with the existence of the mt_srand() function, which accepts arbitrary seed values. Reproducible results are necessary for implementations that need to be reproduced, such as game logic or test code.
-These global states also affect the forked child processes. In fact, the EasySwoole Swoole extension based framework has been alerted to this behavior[5]+
  
-In other languagesRNGs are implemented as objectsso this problem doesn't exists[3] [4]+On the other handif you want to get a true "completely" random resultthe results of the shuffle(), str_shuffle(), and array_rand() functions are not cryptographically secure. This is due to the use of Mersenne Twister internally.
  
-The global state of MT is also used by other functions that use random numbers, and this problem is further exacerbated when the consistency of the results is required by seeding with specific values. (Of courseyou are right that such usage is a bad example.)+The first way to work around this problem is to implement RNG in PHP. In factsuch a library exists and is available. 
 + 
 +However, the PHP implementation of RNG has execution speed issues. This is also the case in PHP 8.x when JIT is enabled. 
 + 
 +**PHP 8.1-dev** 
 +<code shell> 
 +$ git clone "https://github.com/savvot/random" 
 +$ time ./php -r 'require __DIR__ . "/random/src/AbstractRand.php"; require __DIR__ . "/random/src/XorShiftRand.php"; $r = new Savvot\Random\XorShiftRand(1234); for ($i = 0; $i < 1000000; $i++) { $r->random(); }' 
 + 
 +real    0m0.745s 
 +user    0m0.744s 
 +sys     0m0.000s 
 +</code> 
 + 
 +**PHP 8.1-dev + OPcache JIT** 
 +<code shell> 
 +$ git clone "https://github.com/savvot/random" 
 +$ time ./php -dzend_extension="$(pwd)/../../modules/opcache.so" -dopcache.jit_buffer_size=100M -dopcache.enable_cli=1 -r 'require __DIR__ . "/random/src/AbstractRand.php"; require __DIR__ . "/random/src/XorShiftRand.php"; $r = new Savvot\Random\XorShiftRand(1234); for ($i = 0; $i < 1000000; $i++) { $r->random(); }' 
 + 
 +real    0m0.083s 
 +user    0m0.081s 
 +sys     0m0.002s 
 +</code> 
 + 
 +**RFC Implementation (based PHP 8.1-dev)** 
 +<code shell> 
 +$ time ./php -r '$r = new \RNG\XorShift128Plus(1234); for ($i = 0; $i < 1000000; $i++) { rng_next($r); }' 
 + 
 +real    0m0.021s 
 +user    0m0.010s 
 +sys     0m0.011s 
 +</code> 
 + 
 +RFC has been passed and Fiber will be introduced in PHP 8.1. Implementations with unpredictable execution order, such as Fiber, make this problem worse. 
 +For example (with amphp), the following results are difficult for the user to be aware of and are not guaranteed to be consistent in the future.
  
 <code php> <code php>
 +use function Amp\defer;
 +use function Amp\delay;
 +
 +function task(int $i): void {
 +    global $running;
 +
 +    while ($running) {
 +        delay(250);
 +        echo "${i} : " . mt_rand() . "\n";
 +    }
 +}
 +
 mt_srand(1234); mt_srand(1234);
-$arr [123, 4, 5]+ 
-shuffle($arr); +$running true; 
-echo print_r($arr, true); // This result is always consistent.+ 
 +defer(fn() => task(1)); 
 +defer(fn() => task(2)); 
 +defer(fn() => task(3))
 +defer(fn() => task(4)); 
 + 
 +delay(1000); 
 +$running = false;
  
 /* /*
-Array +Result: 
-( +1 : 411284887 
-    [0] => +4 : 1068724585 
-    [1] => +2 : 1335968403 
-    [2] => 5 +: 1756294682 
-    [3] => +: 940013158 
-    [4] => 1 +3 : 1314500282 
-)+4 : 1686544716 
 +: 1656482812 
 +1 : 1674985287 
 +: 1848274264 
 +: 585388171 
 +: 323490420 
 +: 593702477 
 +3 : 426315791 
 +2 : 1722007381 
 +1 : 1750549071
 */ */
 </code> </code>
  
-Thereforeit may be a good idea to consider deprecating global state-dependent RNG functions in the future.+In additionproblems with having state in the global scope have been reported in some extensions. For example, the Swoole extension notes that the use of mt_rand() requires reinitialization in the process after forking.
  
-One currently possible userland solution is to implement the PRNG in pure PHPThere is actually a userland library [1], but it is not fast enough for PHP at the moment, including with JIT (Benchmark results are available at Open Issues.)+https://www.easyswoole.com/En/Other/random.html
  
-This implementation will also allow us to support the PHP paradigm, which will become even more complex in the future.+===== Proposal ===== 
 +Implements class-based object scoped PRNG into PHP.
  
-I have created an extension for PHP to improve these [2]. This could be used to consider what specific goals this RFC is trying to achieve.+First, implement the following interface. This is a hypothetical PHP code.'
  
-===== Proposal =====+Basically, this interface are supposed to be used as arguments to one of the functions. In other words, the next() and next64() methods are not intended to be called directly. next64() returns an invalid value in a 32-bit environment.
  
-Implements an object-scoped PRNG in PHP, providing methods equivalent to functions that use RNG results.+<code php> 
 +namespace RNG;
  
-First, it provides the following interface.+interface RNGInterface 
 +
 +    /** Generates 32bit pseudo random number*/ 
 +    public function next(): int; 
 + 
 +    /** Genrates 64bit pseudo random nunber */ 
 +    public function next64(): int; 
 +
 +</code>
  
-RNG64Interface has a next64() method that returns a 64-bit wide result, but this is not necessary in a 32-bit environment. +The next step is to implement the RNG classes that implement this interfaceThis RFC proposes implementations of XorShift128+MT19937 (similar to mt_srand()), and OS provided (similar to random_bytes()).
-In a 64-bit environmentit is used when trying to generate a number in a range greater than 32 bits.+
  
-The next64() method throws a ValueError exception when running on a non-64bit architecture or not supported RNG class.+These implementations are done in C and are fast. However, by implementing RNGInterface, we can do the same thing in PHP code.
  
 <code php> <code php>
 namespace RNG; namespace RNG;
  
-interface RNGInterface+class XorShift128Plus implements RNGInterface // Fast modern PRNG.
 { {
-    public function next(): int;+    public function __construct(int $seed) {} 
 +    public function next(): int {} 
 +    public function next64(): int {} 
 +    public function __serialize(): array {} 
 +    public function __unserialize(array $data): void {}
 } }
  
-interface RNG64Interface extends RNGInterface+class MT19937 implements RNGInterface // Completely consistent \mt_srand() and \mt_rand() implementation.
 { {
-    /** @throws ValueError *+    public function __construct(int $seed) {} 
-    public function next64(): int;+    public function next(): int {} 
 +    public function next64(): int {} 
 +    public function __serialize(): array {} 
 +    public function __unserialize(array $data): void {} 
 +
 + 
 +class OS implements RNGInterface // // Cryptographically Secure PRNG. 
 +
 +    public function next(): int {} 
 +    public function next64(): int {}
 } }
 </code> </code>
  
-Next, make some changes to the existing functions and add some new ones.+Some RNG implementations can serialize state using the standard PHP serialization methods (serialize() and unserialize() function). This is useful for the purpose of storing state.
  
 <code php> <code php>
-function shuffle(array &$array, ?RNGInterface $rng = null): bool {} +$rng = new RNG\XorShift128Plus(1234); 
-function str_shuffle(string $string, ?RNGInterface $rng = null): string {} +  
-function array_rand(array $array, int $num 1, ?RNGInterface $rng = null): int|string|array {} +\rng_next($rng)
-/** Generates a random number for the specified range using RNG. */ +  
-function rng_range(RNGInterface $rng, int $min, int $max): int [} +$serialized_string \serialize($rng); 
-/** Generates a sequence of bytes for a specified range using RNG. */ +  
-function rng_bytes(RNGInterface $rng, int $length): string {}+$rng2 = \unserialize($serialized_string); 
 +  
 +\rng_next($rng) === rng_next($rng2); // true
 </code> </code>
  
-Existing RNG-specifying functions will now be able to explicitly specify the source of the RNG. This makes it clear that these functions are using the RNG internally.+For existing functions that use RNGs, make changes to accept these classes as arguments. If an argument is specified, the function will use that RNG instead of the internal MT.
  
-Finallywe provide an RNG class that implements these interfaces. +<code php> 
-At this timeconsidering support for XorShift128+ MT19937 and OSRNG.+function shuffle(array &$array?RNG\RNGInterface $rng = null): bool {} 
 + 
 +function str_shuffle(string $string?RNG\RNGInterface $rng = null): string {} 
 + 
 +function array_rand(array $arrayint $num = 1, ?RNG\RNGInterface $rng = null): int|string|array {} 
 +</code> 
 + 
 +Finally, implement a function that can generate values from RNGs, such as the mt_rand(), random_bytes() function. If the $unsigned argument is false, it will return the value generated by the RNG as is.
  
 <code php> <code php>
-namespace RNG;+function rng_bytes(RNG\RNGInterface $rng, int $length): string {} // simlar random_bytes()
  
-final class XorShift128Plus implements RNG64Interface {} // use XorShift128+ algorithm +function rng_int(RNG\RNGInterface $rng, int $min, int $max): int {} // simlar mt_rand() with optional arguments 
-final class MT19937 implements RNG64Interface {} // use MT19937 algorithm + 
-final class OSRNG implements RNG64Interface {} // use php_random_bytes() internal API+function rng_next(RNG\RNGInterface $rng, bool $unsigned = true): int {} // simlar mt_rand() without optional arguments 
 + 
 +/** @throws ValueError */ 
 +function rng_next64(RNG\RNGInterface $rng, bool $unsigned = true): int {} // Generates 64bit random number
 </code> </code>
  
-===== Backward Incompatible Changes =====+The rng_next64() function will throw a ValueError exception if 64-bit integer is not available on the platform.
  
-With the provides of new classes, some class names (or namespaceswill no longer be available in userland.+This is for proper handling of next64() in a 32-bit environment and to improve interoperability with the mt_rand() function. The mt_rand() function performs a bit shift on the result and always returns an unsigned integer.
  
-Some of the functions that use RNGs will have additional optional $rng arguments.+<code php> 
 +// If the second argument is true (default), rng_next() performs bit shifting like mt_rand() and always returns an unsigned integer. 
 +\mt_srand(1234); 
 +$mt_state = new \RNG\MT19937(1234); 
 +\mt_rand() === \rng_next($mt_state); // true 
 +  
 +// If false, it will return the value as is. This is exactly the same result as $rng->next(). 
 +\mt_rand() === \rng_next($mt_state, false); // false 
 +  
 +// This is useful if you want to use the numbers generated by the RNG directly. 
 +\rng_next(new \RNG\MT19937(1234), false) === 822569775; // true 
 +</code> 
 + 
 +===== Backward Incompatible Changes ===== 
 +A new optional argument will be added to the existing arguments below. If you are using reflection for these functions, this may cause problems.
  
   * shuffle()   * shuffle()
Line 125: Line 251:
  
 ==== To Existing Extensions ==== ==== To Existing Extensions ====
-orng [[https://pecl.php.net/package/orng]] : it is a PECL extension that provides almost the same functionality. If the interface is provided by the core in the future, it will need to be supported. And that's me.+none
  
 ==== To Opcache ==== ==== To Opcache ====
Line 137: Line 263:
  
 ===== Open Issues ===== ===== Open Issues =====
 +=== In other languages, what methods do you use to get around this problem? ===
 +Similar to this proposal, a class-based implementation is in place.
  
-=== With JIT, won't the userland implementation reach a useful speed? === +  * C# https://docs.microsoft.com/en-us/dotnet/api/system.random 
-Comparing the speed of the userland implementation of XorShift128+ and the orng extension.+  * Java https://docs.oracle.com/javase/8/docs/api/java/util/Random.html
  
-**PHP 8.0** +===== Unaffected PHP Functionality ===== 
-<code shell> +It does not affect any related existing functions.
-$ time php -r 'require __DIR__ . "/vendor/savvot/random/src/AbstractRand.php"; require __DIR__ . "/vendor/savvot/random/src/XorShiftRand.php"; $r new Savvot\Random\XorShiftRand(1234); for ($i 0; $i < 1000000; $i++) { $r->random(); }' +
- +
-real 0m0.441s +
-user 0m0.429s +
-sys 0m0.010s +
-</code>+
  
-**PHP 8.0 + OPcache JIT** 
-<code shell> 
-$ time php -dopcache.jit_buffer_size=100M -dopcache.enable_cli=1 -r 'require __DIR__ . "/vendor/savvot/random/src/AbstractRand.php"; require __DIR__ . "/vendor/savvot/random/src/XorShiftRand.php"; $r = new Savvot\Random\XorShiftRand(1234); for ($i = 0; $i < 1000000; $i++) { $r->random(); }' 
- 
-real 0m0.155s 
-user 0m0.139s 
-sys 0m0.015s 
-</code> 
- 
-**PHP 8.0 + orng** 
-<code shell> 
-$ time php -r '$r = new \ORNG\XorShift128Plus(1234); for ($i = 0; $i < 1000000; $i++) { $r->next(); }' 
- 
-real 0m0.056s 
-user 0m0.048s 
-sys 0m0.008s 
-</code> 
- 
-This provides a significant improvement, but still slow from the C implementation. 
- 
-=== Why do we need this feature in the core and not in the extension? === 
-In order to use the features related to pseudo-random numbers that PHP currently provides, an understanding of the core is required. If this proposal is implemented, users will be able to use pseudo-random numbers under the easy to understand concept of objects. This is a useful improvement to the overall functionality of the language. 
- 
-===== Unaffected PHP Functionality ===== 
-It does not affect any related existing functions. (However, in the case of Type II, non-destructive arguments will be added.) 
   * mt_srand()   * mt_srand()
   * mt_rand()   * mt_rand()
-  * shuffle() 
-  * str_shuffle() 
-  * array_rand() 
  
-===== Proposed Voting Choices ===== +===== Vote ===== 
-Yes/No, requiring 2/3 majority+Voting opens 2021-04-01 and 2021-04-15 at 00:00:00 EDT. 2/3 required to accept.
  
-There are a few additional options for implementation. +<doodle title="Add object-scoped RNG" auth="zeriyoshi" voteType="single" closed="true"> 
- +   Yes 
-<doodle title="Which implementation looks good?" auth="user" voteType="single" closed="true"> +   No
-   Type I +
-   Type II +
-</doodle> +
- +
-<doodle title="To which namespace should these classes and interfaces belong?" auth="user" voteType="single" closed="true"> +
-   * Top Level (\RNGInterface) +
-   * "RNG" namespace (\RNG\RNGInterface) +
-   * "PHP\RNG" namespace (\PHP\RNG\RNGInterface)+
 </doodle> </doodle>
  
 ===== Patches and Tests ===== ===== Patches and Tests =====
-  * https://github.com/php/php-src/pull/6568 (Type I [outdated]) +  * https://github.com/php/php-src/pull/6568
-  * https://github.com/zeriyoshi/php-src/tree/object_scope_rng_type2 (Type II) +
- +
-===== References ===== +
-  * [1] https://github.com/savvot/random +
-  * [2] https://github.com/zeriyoshi/php-ext-orng +
-  * [3] https://docs.microsoft.com/en-us/dotnet/api/system.random +
-  * [4] https://docs.oracle.com/javase/8/docs/api/java/util/Random.html +
-  * [5] https://www.easyswoole.com/En/Other/random.html+
rfc/object_scope_prng.1610874482.txt.gz · Last modified: 2021/01/17 09:08 by zeriyoshi