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Resumptions in final cycle collection after EventLoop return in DriverSuspension are ignored #90

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bwoebi opened this issue Dec 23, 2023 · 0 comments · May be fixed by #99
Open

Resumptions in final cycle collection after EventLoop return in DriverSuspension are ignored #90

bwoebi opened this issue Dec 23, 2023 · 0 comments · May be fixed by #99

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@bwoebi
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bwoebi commented Dec 23, 2023

Consider these test cases (the one case immediately resumes in cycle collection, the other schedules something on the event loop):

    public function testSuspensionResumptionWithQueueInGarbageCollection(): void
    {
        $suspension = EventLoop::getSuspension();

        $class = new class($suspension) {
            public function __construct(public Suspension $suspension) {}
            public function __destruct() { $this->suspension->resume(true); }
        };
        $cycle = [$class, &$cycle];
        unset($class, $cycle);

        $ended = $suspension->suspend();

        $this->assertTrue($ended);
    }

    public function testEventLoopResumptionWithQueueInGarbageCollection(): void
    {
        $suspension = EventLoop::getSuspension();

        $class = new class($suspension) {
            public function __construct(public Suspension $suspension) {}
            public function __destruct() { EventLoop::queue($this->suspension->resume(...), true); }
        };
        $cycle = [$class, &$cycle];
        unset($class, $cycle);

        $ended = $suspension->suspend();

        $this->assertTrue($ended);
    }

These cases both will fail with:

Error: Event loop terminated without resuming the current suspension (the cause is either a fiber deadlock, or an incorrectly unreferenced/canceled watcher):

(The trailing colon is also weird, it means that no other fibers exist, maybe write that out.)

I was initially very confused when this happened in my code as dumping the event loop showed a pending queue() call, while the EventLoop reported as finished.

I would expect that, after the gc_collect_cycles():

event-loop/src/EventLoop/Internal/DriverSuspension.php

Line 129 in 25de49a

\gc_collect_cycles(); // Collect any circular references before dumping pending suspensions.

the EventLoop is checked for any active, referenced watchers or microtasks, and if yes, is resumed. Similarly, if a suspension was resumed within that cycle collection, it will leave the code path leading to the error being thrown.
@danog danog linked a pull request Dec 6, 2024 that will close this issue
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Allow queueing of callbacks in destructors danog/event-loop
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@bwoebi