*** Error in `php': malloc(): 0x000055c853bafde0 *** and e.t.c

[antonim]

Hello. When I use code:

for ($i = 0; $i < 1000; $i++) {
    Loop::run(function ()  {
        $threads = [];
        for ($i = 0; $i < 100; $i++) {

            $threads[] = Thread::spawn(function () {
                return rand(1,100);
            });
        }

        foreach ($threads as $thread) {
            $thread->join();
        }
    });
    echo $i . "\n";
}

Everytime I'v get system error ex:

*** Error in `php': malloc(): memory corruption (fast): 0x0000000002209ee2 ***
Aborted (core dumped)

or

Segmentation fault (core dumped)

or

*** Error in `php': free(): invalid pointer: 0x00005579a7f2157d ***

or

*** Error in `php': corrupted double-linked list: 0x000055ca863cc7e0 ***

This can happen after the third iteration and can be after 1000 iterations. I can not find the relationship between the number of iterations and the receipt of this error.

Could you tell me how can I avoid that problem?

[trowski]

You are attempting to spawn 100 * 1000 = 100,000 threads as fast as possible. I would never expect something like this to work. Honestly I'm impressed you get any sort of output. To see something actually work, simply add yield in front of $thread->join(), which will wait for the 100 threads to exit before attempting to spawn another 100 threads.

[bwoebi]

@trowski It actually should wait anyway on the threads to exit first as we have open I/O watchers as long as they exist.
I don't think that's the issue.

[trowski]

@antonim It was pointed out to me by @bwoebi that I missed the obvious: Loop::run() should not exit until the first 100 threads have exited since there will be active watchers in the loop, so only 100 threads should be spawned at a time (which definitely should work fine). I'll look deeper into what might be happening here.

[kelunik]

@antonim I guess you have some extension enabled that isn't thread-safe?

[krakjoe]

So I reproduced the error, it would appear that this originates in PHP itself, at the point where INI entries are copied for new threads - not by pthreads but by ZE - I vaguely remember someone mentioning that this was a problem since we started refcounting strings, but I don't remember the detail.

Let me poke a few people and see what I can find out ...

[krakjoe]

The best advice right now seems to be use pre-release builds of 7.2 with pthreads ... ZTS is broken in 7.0 and 7.1 ... I'm not sure why we didn't fix it when we first became aware of it, but we didn't, and I'm not sure how reasonable it is to back port the changes (zts supports interned strings in 7.2, which are not refcounted), and I don't know who has the appetite or time (I probably don't).

[krakjoe]

This is the commit that fixed it: php/php-src@c698299

It contains ABI breaks, so 7.2 requirement is the only reasonable thing to do ... sorry about that ...

[kelunik]

@krakjoe Thanks for looking into this. It's now segfaulting instead of having that memory corruption error on 7.2.0beta1.

[kelunik]

This runs fine now with the latest pthreads and PHP 7.2.0beta1.