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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