Memory leak in Ds\Set and Ds\Map when using Ds\Hashable as a key

[WebOtaku]

Hello everyone. The problem arises when we place an object belonging to a class implementing the Ds\Hashable interface into a Ds\Set or when we use it as a key in a Ds\Map.

Example:

<?php

class HashableObj implements \Ds\Hashable // No memory leak if not implements \Ds\Hashable
{
    public static int $countDestroyed = 0;

    public function __construct(public int $id, public string $name)
    {
    }

    public function __destruct()
    {
        ++self::$countDestroyed;
    }

    public function hash(): string
    {
        // return md5($this->id . '|' . $this->name);   // More memory leaked with bigger hashes
        // return crc32($this->id . '|' . $this->name);
        // return $this->id & 0x0f;                     // Less leaks with small hashes
        return $this->id;
    }

    public function equals($obj): bool
    {
        if (!$obj instanceof \app\commands\HashableObj) {
            return false;
        }

        return $this->id === $obj->id && $this->name === $obj->name;
    }
}

$baseMemory = memory_get_usage(true);
echo "Memory usage (start): " . (int)($baseMemory / 1048576) . " MB" . PHP_EOL;

$objectsCreated = 0;

for ($i = 0; $i < 25; $i++) {
    srand((new DateTimeImmutable())->getTimestamp());

    $map = new \Ds\Map();
    $map->allocate(50000);

    for ($j = 0; $j < 50000; $j++) {
        ++$objectsCreated;
        $map->put(new HashableObj(rand(1, 50000), "test_$j"), $j);
        // $map->put($j, new HashableObj(rand(1, 50000), "test_$j")); // No memory leak
    }

    $map->clear();

    echo "Memory usage: " . (int)((memory_get_usage(true) - $baseMemory) / 1048576) . " MB" . PHP_EOL;
    echo "Memory peak usage: " . (int)(memory_get_peak_usage(true) / 1048576) . " MB" . PHP_EOL;
    echo "$objectsCreated objects created" . PHP_EOL;
    echo HashableObj::$countDestroyed . " objects destroyed" . PHP_EOL;
}

echo "Memory usage (end): " . (int)((memory_get_usage(true) - $baseMemory) / 1048576) . " MB" . PHP_EOL;

Result:

Memory usage (start): 2 MB
Memory usage: 8 MB
Memory peak usage: 12 MB
50000 objects created
50000 objects destroyed
Memory usage: 10 MB
Memory peak usage: 14 MB
100000 objects created
100000 objects destroyed
Memory usage: 10 MB
Memory peak usage: 14 MB
150000 objects created
150000 objects destroyed
Memory usage: 12 MB
Memory peak usage: 16 MB
200000 objects created
200000 objects destroyed
Memory usage: 14 MB
Memory peak usage: 18 MB
250000 objects created
250000 objects destroyed
Memory usage: 16 MB
Memory peak usage: 20 MB
300000 objects created
300000 objects destroyed
Memory usage: 16 MB
Memory peak usage: 20 MB
350000 objects created
350000 objects destroyed
Memory usage: 18 MB
Memory peak usage: 22 MB
400000 objects created
400000 objects destroyed
Memory usage: 20 MB
Memory peak usage: 24 MB
450000 objects created
450000 objects destroyed
Memory usage: 22 MB
Memory peak usage: 26 MB
500000 objects created
500000 objects destroyed
Memory usage: 22 MB
Memory peak usage: 26 MB
550000 objects created
550000 objects destroyed
Memory usage: 24 MB
Memory peak usage: 28 MB
600000 objects created
600000 objects destroyed
Memory usage: 26 MB
Memory peak usage: 30 MB
650000 objects created
650000 objects destroyed
Memory usage: 28 MB
Memory peak usage: 32 MB
700000 objects created
700000 objects destroyed
Memory usage: 28 MB
Memory peak usage: 32 MB
750000 objects created
750000 objects destroyed
Memory usage: 30 MB
Memory peak usage: 34 MB
800000 objects created
800000 objects destroyed
Memory usage: 32 MB
Memory peak usage: 36 MB
850000 objects created
850000 objects destroyed
Memory usage: 34 MB
Memory peak usage: 38 MB
900000 objects created
900000 objects destroyed
Memory usage: 36 MB
Memory peak usage: 40 MB
950000 objects created
950000 objects destroyed
Memory usage: 36 MB
Memory peak usage: 40 MB
1000000 objects created
1000000 objects destroyed
Memory usage: 38 MB
Memory peak usage: 42 MB
1050000 objects created
1050000 objects destroyed
Memory usage: 40 MB
Memory peak usage: 44 MB
1100000 objects created
1100000 objects destroyed
Memory usage: 42 MB
Memory peak usage: 46 MB
1150000 objects created
1150000 objects destroyed
Memory usage: 42 MB
Memory peak usage: 46 MB
1200000 objects created
1200000 objects destroyed
Memory usage: 44 MB
Memory peak usage: 48 MB
1250000 objects created
1250000 objects destroyed
Memory usage (end): 44 MB

Environment:

PHP 8.1.28 (cli) (built: Apr 22 2024 09:45:11) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.1.28, Copyright (c) Zend Technologies
    with Zend OPcache v8.1.28, Copyright (c), by Zend Technologies
    with Xdebug v3.3.2, Copyright (c) 2002-2024, by Derick Rethans

DS extension ver.: 1.6.0

[PHP Modules]
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Zend OPcache
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[Zend Modules]
Xdebug
Zend OPcache

This problem was also observed on PHP 8.3 with the DS extension version 1.5.0.

[ndossche]

Fix here: #218