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101 lines
3.1 KiB
C++
101 lines
3.1 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set sw=2 ts=8 et ft=cpp : */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_ipc_AsyncBlockers_h
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#define mozilla_ipc_AsyncBlockers_h
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#include "mozilla/ThreadSafety.h"
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#include "nsTArray.h"
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// FIXME: when bug 1760855 is fixed, it should not be required anymore
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namespace mozilla::ipc {
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/**
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* AsyncBlockers provide a simple registration service that allows to suspend
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* completion of a particular task until all registered entries have been
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* cleared. This can be used to implement a similar service to
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* nsAsyncShutdownService in processes where it wouldn't normally be available.
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* This class is thread-safe.
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*/
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class AsyncBlockers {
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public:
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AsyncBlockers()
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: mLock("AsyncRegistrar"),
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mPromise(new GenericPromise::Private(__func__)) {}
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void Register(void* aBlocker) {
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MutexAutoLock lock(mLock);
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if (mResolved) {
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// Too late.
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return;
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}
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mBlockers.InsertElementSorted(aBlocker);
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}
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void Deregister(void* aBlocker) {
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MutexAutoLock lock(mLock);
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if (mResolved) {
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// Too late.
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return;
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}
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MOZ_ASSERT(mBlockers.ContainsSorted(aBlocker));
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MOZ_ALWAYS_TRUE(mBlockers.RemoveElementSorted(aBlocker));
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MaybeResolve();
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}
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RefPtr<GenericPromise> WaitUntilClear(uint32_t aTimeOutInMs = 0) {
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if (!aTimeOutInMs) {
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// We don't need to wait, resolve the promise right away.
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MutexAutoLock lock(mLock);
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if (!mResolved) {
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mPromise->Resolve(true, __func__);
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mResolved = true;
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}
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} else {
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GetCurrentEventTarget()->DelayedDispatch(
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NS_NewRunnableFunction("AsyncBlockers::WaitUntilClear",
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[promise = mPromise]() {
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// The AsyncBlockers object may have been
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// deleted by now and the object isn't
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// refcounted (nor do we want it to be). We
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// can unconditionally resolve the promise
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// even it has already been resolved as
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// MozPromise are thread-safe and will just
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// ignore the action if already resolved.
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promise->Resolve(true, __func__);
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}),
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aTimeOutInMs);
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}
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return mPromise;
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}
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virtual ~AsyncBlockers() {
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if (!mResolved) {
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mPromise->Resolve(true, __func__);
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}
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}
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private:
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void MaybeResolve() REQUIRES(mLock) {
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mLock.AssertCurrentThreadOwns();
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if (mResolved) {
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return;
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}
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if (!mBlockers.IsEmpty()) {
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return;
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}
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mPromise->Resolve(true, __func__);
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mResolved = true;
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}
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Mutex mLock;
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nsTArray<void*> mBlockers GUARDED_BY(mLock);
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bool mResolved GUARDED_BY(mLock) = false;
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const RefPtr<GenericPromise::Private> mPromise;
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};
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} // namespace mozilla::ipc
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#endif // mozilla_ipc_AsyncBlockers_h
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