If exit() is called on a thread with an EventLoop in the stack, the
ThreadData storing the array of wake pipes will be destroyed first.
Threads can still take a strong reference to the EventLoop after that,
and will read the fds from freed memory.
Instead, take a copy of the write fd, and swallow EBADF when writing to
it, since that only indicates that the thread and event loop are
exiting, so there's nothing to do with the wake.
Add a thread-safe deferred_invoke() API on WeakEventLoopReference that
queues work onto the owning thread's event queue and wakes that thread
via EventLoopManager hooks. This avoids calling wake() from foreign
threads during teardown.
Implement current_thread_handle()/wake_thread() in each backend and
track per-thread data so handles are validated before waking:
- Unix: wake via per-thread wake pipe
- Windows: wake via thread wake event
- macOS: wake via stored CFRunLoopRef
- Qt: wake via event target or QEventLoop::wakeUp()
- Android: wake via stored ALooper
The DeferredInvocationContext only existed to satisfy the requirement
in ThreadEventQueue that each event has an EventReceiver. However,
deferred_invoke() was not even using the EventReceiver to call its
callback. Therefore, we don't need to allocate one for every deferred
invocation.
This also prevents WeakPtr::strong_ref() from racing and leaking the
context object when invoking a function across threads.
This method was removed in e015a43b51
However, it was not exactly *unused* as the commit message would say.
This method was the only thing that allowed spin_until to exit when
the event loop was cancelled. This happens normally when IPC connections
are closed, but also when the process is killed.
The logic to properly handle process exit from event loop spins needs to
actually notify the caller that their goal condition was not met though.
That will be handled in a later commit.
