1 files changed, 82 insertions, 0 deletions
diff --git a/ipc/glue/AsyncBlockers.h b/ipc/glue/AsyncBlockers.h
new file mode 100644
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+++ b/ipc/glue/AsyncBlockers.h
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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