Magic property access skips __get() when another Fiber is suspended in __get() on the same object

Description

Description

When two Fibers access the same undefined property on the same object, and the
first Fiber suspends inside __get(), the second Fiber does not invoke
__get().

Instead, PHP emits an "Undefined property" warning and returns null.
After the first Fiber is resumed, its property access returns the correct value.

The access from the second Fiber is not a recursive property access. It is an
independent access with its own Fiber execution stack.

The issue reproduces with php -n, without loading a php.ini or third-party
extensions.

Steps to reproduce

Save the following script as fiber-magic-get.php:

<?php

declare(strict_types=1);

final class YieldingProperty
{
    public function __get(string $name): int
    {
        Fiber::suspend();
        return 8;
    }
}

$value = new YieldingProperty();

$first = new Fiber(static function () use ($value): void {
    var_dump($value->property);
});

$second = new Fiber(static function () use ($value): void {
    var_dump($value->property);
});

$first->start();
$second->start();
$first->resume();

Run it without loading configuration or extensions:

php -n fiber-magic-get.php

Actual result

Warning: Undefined property: YieldingProperty::$property ...
NULL
int(8)

__get() is skipped for the second Fiber and the property access returns
null.

Expected result

int(8)
int(8)

Both property accesses should invoke __get() independently and return 8.

Suspending one Fiber inside __get() should not make an access from another
Fiber appear recursive.

Reproducibility

Always reproducible.

Tested with:

• PHP 8.3.33 CLI on Linux, using php -n
• PHP 8.4.7 CLI on Windows, using php -n

Additional information

The issue only occurs when the Fibers share the same object.

The following controls do not fail:

• Giving each Fiber its own object
• Replacing the magic property access with a normal method call on the shared
  object

The same problem also affects __isset() and null-coalescing property
expressions such as:

$value = $object->property ?? 0;

Under contention, these expressions can silently return the fallback value
even though __isset() returns true and __get() returns the expected value.

This behavior suggests that the recursion guard for overloaded properties is
associated with the shared object and remains visible to other Fibers while a
magic property handler is suspended.

PHP Version

PHP 8.3.33 (cli) (built: Jul 31 2026 12:56:07) (NTS)
Copyright (c) The PHP Group
Zend Engine v4.3.33, Copyright (c) Zend Technologies
    with Zend OPcache v8.3.33, Copyright (c), by Zend Technologies

PHP 8.4.7 (cli) (built: May  6 2025 14:12:45) (ZTS Visual C++ 2022 x64)
Copyright (c) The PHP Group
Zend Engine v4.4.7, Copyright (c) Zend Technologies

Operating System

Windows 11, Plesk Linux ... 6.8.0-111-generic #111-Ubuntu SMP PREEMPT_DYNAMIC Sat Apr 11 23:16:02 UTC 2026 x86_64 x86_64 x86_64 GNU/Linux

Bắt đầu với bản tái hiện fiber-magic-get.php được cung cấp và chạy nó bằng php -n, sau đó so sánh đầu ra thực tế với đầu ra mong đợi. Điều tra cơ chế bảo vệ chống đệ quy của thuộc tính overloaded giữa hai Fibers dùng chung đối tượng, bao gồm các trường hợp liên quan đến __isset() và phép kết hợp null; hoàn tất khi cả hai lần truy cập độc lập đều gọi các handler tương ứng và trả về các giá trị mong đợi.