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/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this file,
* You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef WAITFOR_H_
#define WAITFOR_H_
#include "MediaEventSource.h"
#include "mozilla/Maybe.h"
#include "mozilla/Result.h"
#include "mozilla/SpinEventLoopUntil.h"
namespace mozilla {
/**
* Waits for an occurrence of aEvent on the current thread (by blocking it,
* except tasks added to the event loop may run) and returns the event's
* templated value, if it's non-void.
*
* The caller must be wary of eventloop issues, in
* particular cases where we rely on a stable state runnable, but there is never
* a task to trigger stable state. In such cases it is the responsibility of the
* caller to create the needed tasks, as JS would. A noteworthy API that relies
* on stable state is MediaTrackGraph::GetInstance.
*/
template <typename T>
T WaitFor(MediaEventSource<T>& aEvent) {
Maybe<T> value;
MediaEventListener listener = aEvent.Connect(
AbstractThread::GetCurrent(), [&](T aValue) { value = Some(aValue); });
SpinEventLoopUntil<ProcessFailureBehavior::IgnoreAndContinue>(
[&] { return value.isSome(); });
listener.Disconnect();
return value.value();
}
/**
* Specialization of WaitFor<T> for void.
*/
void WaitFor(MediaEventSource<void>& aEvent) {
bool done = false;
MediaEventListener listener =
aEvent.Connect(AbstractThread::GetCurrent(), [&] { done = true; });
SpinEventLoopUntil<ProcessFailureBehavior::IgnoreAndContinue>(
[&] { return done; });
listener.Disconnect();
}
/**
* Variant of WaitFor that blocks the caller until a MozPromise has either been
* resolved or rejected.
*/
template <typename R, typename E, bool Exc>
Result<R, E> WaitFor(const RefPtr<MozPromise<R, E, Exc>>& aPromise) {
Maybe<R> success;
Maybe<E> error;
aPromise->Then(
GetCurrentSerialEventTarget(), __func__,
[&](R aResult) { success = Some(aResult); },
[&](E aError) { error = Some(aError); });
SpinEventLoopUntil<ProcessFailureBehavior::IgnoreAndContinue>(
[&] { return success.isSome() || error.isSome(); });
if (success.isSome()) {
return success.extract();
}
return Err(error.extract());
}
/**
* A variation of WaitFor that takes a callback to be called each time aEvent is
* raised. Blocks the caller until the callback function returns true.
*/
template <typename T, typename CallbackFunction>
void WaitUntil(MediaEventSource<T>& aEvent, const CallbackFunction& aF) {
bool done = false;
MediaEventListener listener =
aEvent.Connect(AbstractThread::GetCurrent(), [&](T aValue) {
if (!done) {
done = aF(aValue);
}
});
SpinEventLoopUntil<ProcessFailureBehavior::IgnoreAndContinue>(
[&] { return done; });
listener.Disconnect();
}
} // namespace mozilla
#endif // WAITFOR_H_
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