Unsetting variables in a threaded context leads to segfaults.

[jensscherbl]

Especially when using array_shift(), array_pop() etc. in a thread for an array of anonymous functions.

[jensscherbl]

See https://github.com/jensscherbl/threading/blob/master/system/threading/class/QueueStore.php#L59 for an example.

The (memory leaking, debug only) workaround below produces random segfaults as well, but not always and right away.

https://gist.github.com/jensscherbl/8040d244ca8f4cfee436668c52d4355c

[zelgerj]

Ok, could you please provide an executable script to get it reproduced here. thx!

[jensscherbl]

Like this?

https://gist.github.com/jensscherbl/9e7b5c416fbd0a0f57c3491f9ad82807

[zelgerj]

perfect thanks, i'll take a look asap.

[jensscherbl]

Any progress so far?

[zelgerj]

Yes. The garbage collector destroys the list of callables $this->callables because the properties refcount is 1 in this moment. When the gc runs, it will fetch properties, every time so you have to keep care about refcounts on your own to control memory usage as well.

This should work:

<?php

final class Runnable
{
    private $callables;
    public function __construct(callable ...$callables)
    {
        $this->callables = $callables;
    }
    public function run()
    {
        // add ref count by assigning local function scope var to avoid gc
        $callables = $this->callables;

        do {
            $callable = array_shift($callables);
            $callable();
        } while (count($callables) > 0);
    }
}

$runnable = new Runnable(
    function () { echo 'Task 1.' . PHP_EOL; },
    function () { echo 'Task 2.' . PHP_EOL; },
    function () { echo 'Task 3.' . PHP_EOL; },
    function () { echo 'Task 4.' . PHP_EOL; },
    function () { echo 'Task 5.' . PHP_EOL; }
);

$id = null;
$handle = null;

fhread_create(
    $runnable,
    $id,
    $handle
);

fhread_join(
    $handle,
    $error
);

I also noticed that your script ends up with a seq-fault. I'll check this later.

Task 1.
Task 2.
Task 3.
Task 4.
Task 5.
[1]    37678 segmentation fault  sapi/cli/php test.php

You may want to have a look here where i've implemented your logic by using the fhreads lib Threadclass which does not end up with a seq-fault as an example: https://github.com/appserver-io/fhreads/blob/master/examples/Runnable.php

Cheers

[jensscherbl]

I also noticed that your script ends up with a seq-fault.

To be honest, I just assumed the segfault was a direct result of the gc issue.

i've implemented your logic by using the fhreads lib Threadclass which does not end up with a seq-fault

Kinda weird since the Thread class doesn't really do anything different under the hood. Could it be that this also has something to do with reference issues?

// add ref count by assigning local function scope var to avoid gc

How could this (temporary?) workaround be implemented for a simple Worker class?

https://gist.github.com/jensscherbl/fba47d61356e3f2e4e4bd9b39efa88c4

[zelgerj]

just temp. add

    public function run()
    {
        // add ref count by assigning local function scope var to avoid gc
        $callables = $this->callables;

to your workers run function.

cheers.

[jensscherbl]

just temp. add

Ah, got it. I somehow assumed it would create a thread-local copy instead of a reference. Not sure why...

[zelgerj]

ok. i'll leave this issue open until i was able to check if a fix on internals gc manipulation is possible. I'll keep it updated

[jensscherbl]

Let me know if there's anything I can do to help.