The audio enqueuer thread goes to sleep when there is no more audio data
present, and through normal Core::EventLoop events it can be woken up.
However, that waking up only happens when the thread is not currently
running, so that the wake-up events don't queue up and cause weirdness.
The atomic variable responsible for keeping track of whether the thread
is active can lead to a racy deadlock however, where the audio enqueuer
thread will never wake up again despite there being audio data to
enqueue. Consider this scenario:
- Main thread calls into async_enqueue. It detects that according to the
atomic variable, the other thread is still running, skipping the event
queue wake.
- Enqueuer thread has just finished playing the last chunk of audio and
detects that there is no audio left. It enters the if block with the
dbgln "Reached end of provided audio data..."
- Main thread enqueues audio, making the user sample queue non-empty.
- Enqueuer thread does not check this condition again, instead setting
the atomic variable to indicate that it is not running. It exits into
an event loop sleep.
- Main thread exits async_enqueue. The calling audio enqueuing system
(see e.g. Piano, but all of them function similarly) will wait until
the enqueuer thread has played enough samples before async_enqueue is
called again. However, since the enqueuer thread will never play any
audio, this condition is never fulfilled and audio playback deadlocks
This commit fixes that by allowing the event loop to not enqueue an
event that already exists, therefore overloading the audio enqueuer
event loop by at maximum one message in weird situations. We entirely
get rid of the atomic variable and the race condition is prevented.
The main event loop functionality was used in just two places where the
alternative is a bit simpler. Remove it in favor of referencing the
event loop directly, or just invoking `EventLoop::current()`.
Note that we don't need locking in the constructor since we're now only
modifying a thread-local `Vector`. We also don't need locking in the
old call sites to `::with_main_locked()` since we already lock the
event loop in the subsequent `::post_event()` invocation.
Because the wake pipe is thread-local, it was previously not possible
to wake an event loop across a thread. Therefore, this commit
rearchitects event loop waking by making the wake function a member of
the event loop itself and having it keep a pointer to its thread's wake
pipe. The global wake() function calls wake on the current thread's
event loop.
This also fixes a bug in BackgroundAction: it should wake the event loop
it was created on, instead of the current thread's event loop.
After the previous change, the wake pipe was only being created on the
main thread by the main event loop. This change utilizes a flag to
always initialize the wake pipe on other threads. Because the pipe is
quite expensive (it will count towards the file descriptor limit, for
instance), we do the initialization "lazily": Only when an event loop is
constructed and it notices that there hasn't been a wake pipe created on
its thread, it will create the pipe. Conversely, this means that there
are no pipes on threads that never use an event loop.
The event loop system was previously very singletony to the point that
there's only a single event loop stack per process and only one event
loop (the topmost) can run at a time. This commit simply makes the event
loop stack and related structures thread-local so that each thread has
an isolated event loop system.
Some things are kept at a global level and synchronized with the new
MutexProtected: The main event loop needs to still be obtainable from
anywhere, as it closes down the application when it exits. The ID
allocator is global as IDs should not be shared even between threads.
And for the inspector server connection, the same as for the main loop
holds.
Note that currently, the wake pipe is only created by the main thread,
so notifications don't work on other threads.
This removes the temporary mutex fix for notifiers, introduced in
0631d3fed5 .
Sometimes, pumping the event loop will cause new events to be
generated. For example, an IPC message could be delivered which then
dispatches a new event to be handled by the GUI. To the invoker of
`EventLoop::pump()`, it is not obvious if any events were processed at
all.
Libraries like SDL2 might not have the opportunity to run the event
loop often enough that events can be processed swiftly, since it might
spend time doing other things. This can result in stuttering GUI
interactions.
This changes `EventLoop::pump()` to return the number of processed
events. This functionality will be used by our SDL2 port in another PR.
Core::deferred_invoke is a way of executing an action after previously
queued events have been processed. It removes the requirement of
having/being a Core::Object subclass in order to defer invocation
through Core::Object::deferred_invoke.
Core::Object::deferred_invoke now delegates to Core::deferred_invoke.
The version with the Object& argument is still present but will be
removed in the following commits.
This commit additionally fixes a new places where the
DeferredInvocationEvent was dispatched to the event loop directly, and
replaces them with the Core::deferred_invoke equivalent.
This static bool getter can be used to VERIFY that an event loop exists,
in situations where one is expected.
This is helpful if the absence of an event loop would generate strange
and/or loud errors that don't immediately point to this as a cause.
This functionality, while neat, isn't really something you need enabled
all the time. Let's make it opt-in instead. Pass MakeInspectable::Yes
to the Core::EventLoop constructor if you want your program to become
inspectable.
Core::EventLoop now makes an outbound connection to InspectorServer
instead of listening for incoming connections on a /tmp/rpc/PID socket.
This has many benefits, for example:
- We no longer keep an open listening socket in most applications
- We stop leaking socket files in /tmp/rpc
- We can tighten the pledges in many programs (patch coming)
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
