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Date: Sat, 26 Jun 2021 09:39:52 +0900
Message-ID: <CABTDVhD9SKNVFrt8NMj4BqdHmsMpSt0DH=SMmb-9C905rgc7PA@mail.gmail.com>
To: PHP internals <internals@lists.php.net>
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Subject: [RFC] Add Random Extension (before: Add Random class)
From: zeriyoshi@gmail.com (Go Kudo)

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Content-Type: text/plain; charset="UTF-8"

Hello Internals.

RFC has been reorganized for finalization.

https://wiki.php.net/rfc/rng_extension

The changes from the previous version are as follows:

- Changed again to a class-based approach. The argument can be omitted, in
which case an instance of XorShift128Plus will be created automatically.
- Future scope was specified in the RFC and the functionality was separated
as a Random extension.
- Changed to separate it as a Random extension and use the appropriate
namespace.
- In order to extend the versatility of the final class, Random, a
RandomInterface has been added, similar in approach to the
DateTimeInterface.

I've done a tidy implementation to make this final, but I'm currently
suffering from error detection by Valgrind for unknown reasons.

Implementation is here: https://github.com/php/php-src/pull/7079

This can be reproduced with the following code.

```sh
# Success
$ valgrind ./sapi/cli/php -r '$random = new Random(); $random->nextInt();'
==95522== Memcheck, a memory error detector
==95522== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==95522== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==95522== Command: ./sapi/cli/php -r $random\ =\ new\ Random();\
$random-\>nextInt();
==95522==
==95522==
==95522== HEAP SUMMARY:
==95522==     in use at exit: 1,286 bytes in 32 blocks
==95522==   total heap usage: 28,445 allocs, 28,413 frees, 4,333,047 bytes
allocated
==95522==
==95522== LEAK SUMMARY:
==95522==    definitely lost: 0 bytes in 0 blocks
==95522==    indirectly lost: 0 bytes in 0 blocks
==95522==      possibly lost: 0 bytes in 0 blocks
==95522==    still reachable: 1,286 bytes in 32 blocks
==95522==         suppressed: 0 bytes in 0 blocks
==95522== Rerun with --leak-check=full to see details of leaked memory
==95522==
==95522== For counts of detected and suppressed errors, rerun with: -v
==95522== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

# Fail
$ valgrind ./sapi/cli/php -r '$random = new Random(); $random->nextInt()
=== $random->nextInt();'
==95395== Memcheck, a memory error detector
==95395== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==95395== Using Valgrind-3.14.0 and LibVEX; rerun with -h for copyright info
==95395== Command: ./sapi/cli/php -r $random\ =\ new\ Random();\
$random-\>nextInt()\ ===\ $random-\>nextInt();
==95395==
==95395== Conditional jump or move depends on uninitialised value(s)
==95395==    at 0x966925: ZEND_IS_IDENTICAL_SPEC_VAR_VAR_HANDLER
(zend_vm_execute.h:27024)
==95395==    by 0x99AC27: execute_ex (zend_vm_execute.h:57236)
==95395==    by 0x99C902: zend_execute (zend_vm_execute.h:59026)
==95395==    by 0x8DB6B4: zend_eval_stringl (zend_execute_API.c:1191)
==95395==    by 0x8DB861: zend_eval_stringl_ex (zend_execute_API.c:1233)
==95395==    by 0x8DB8D6: zend_eval_string_ex (zend_execute_API.c:1243)
==95395==    by 0xA4DAE4: do_cli (php_cli.c:995)
==95395==    by 0xA4E8E2: main (php_cli.c:1366)
==95395==
==95395==
==95395== HEAP SUMMARY:
==95395==     in use at exit: 1,286 bytes in 32 blocks
==95395==   total heap usage: 28,445 allocs, 28,413 frees, 4,333,070 bytes
allocated
==95395==
==95395== LEAK SUMMARY:
==95395==    definitely lost: 0 bytes in 0 blocks
==95395==    indirectly lost: 0 bytes in 0 blocks
==95395==      possibly lost: 0 bytes in 0 blocks
==95395==    still reachable: 1,286 bytes in 32 blocks
==95395==         suppressed: 0 bytes in 0 blocks
==95395== Rerun with --leak-check=full to see details of leaked memory
==95395==
==95395== For counts of detected and suppressed errors, rerun with: -v
==95395== Use --track-origins=yes to see where uninitialised values come
from
==95395== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
```

However, the detection is internal to the Zend VM and the cause has not
been identified. From the code, it looks like memory management is being
done properly.

I have a somewhat tricky way of allocating memory to make the process
common, do I need to give some hints to Valgrind?

If you know, I would appreciate your advice on this issue.

Regards,
Go Kudo

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