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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set sw=2 ts=8 et ft=cpp : */
/* 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 mozilla_ipc_AsyncBlockers_h
#define mozilla_ipc_AsyncBlockers_h
#include "mozilla/MozPromise.h"
#include "mozilla/ThreadSafety.h"
#include "nsTArray.h"
// FIXME: when bug 1760855 is fixed, it should not be required anymore
namespace mozilla::ipc {
/**
* AsyncBlockers provide a simple registration service that allows to suspend
* completion of a particular task until all registered entries have been
* cleared. This can be used to implement a similar service to
* nsAsyncShutdownService in processes where it wouldn't normally be available.
* This class is thread-safe.
*/
class AsyncBlockers {
public:
AsyncBlockers()
: mLock("AsyncRegistrar"),
mPromise(new GenericPromise::Private(__func__)) {}
void Register(void* aBlocker) {
MutexAutoLock lock(mLock);
mBlockers.InsertElementSorted(aBlocker);
}
void Deregister(void* aBlocker) {
MutexAutoLock lock(mLock);
MOZ_ASSERT(mBlockers.ContainsSorted(aBlocker));
MOZ_ALWAYS_TRUE(mBlockers.RemoveElementSorted(aBlocker));
MaybeResolve();
}
RefPtr<GenericPromise> WaitUntilClear(uint32_t aTimeOutInMs = 0) {
{
MutexAutoLock lock(mLock);
MaybeResolve();
}
if (aTimeOutInMs > 0) {
GetCurrentSerialEventTarget()->DelayedDispatch(
NS_NewRunnableFunction("AsyncBlockers::WaitUntilClear",
[promise = mPromise]() {
// The AsyncBlockers object may have been
// deleted by now and the object isn't
// refcounted (nor do we want it to be). We
// can unconditionally resolve the promise
// even it has already been resolved as
// MozPromise are thread-safe and will just
// ignore the action if already resolved.
promise->Resolve(true, __func__);
}),
aTimeOutInMs);
}
return mPromise;
}
virtual ~AsyncBlockers() { mPromise->Resolve(true, __func__); }
private:
void MaybeResolve() MOZ_REQUIRES(mLock) {
mLock.AssertCurrentThreadOwns();
if (!mBlockers.IsEmpty()) {
return;
}
mPromise->Resolve(true, __func__);
}
Mutex mLock;
nsTArray<void*> mBlockers MOZ_GUARDED_BY(mLock);
const RefPtr<GenericPromise::Private> mPromise;
};
} // namespace mozilla::ipc
#endif // mozilla_ipc_AsyncBlockers_h
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