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-rw-r--r--xpcom/threads/nsThreadSyncDispatch.h65
1 files changed, 65 insertions, 0 deletions
diff --git a/xpcom/threads/nsThreadSyncDispatch.h b/xpcom/threads/nsThreadSyncDispatch.h
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+++ b/xpcom/threads/nsThreadSyncDispatch.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* 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 nsThreadSyncDispatch_h_
+#define nsThreadSyncDispatch_h_
+
+#include "mozilla/Atomics.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/SpinEventLoopUntil.h"
+
+#include "nsThreadUtils.h"
+#include "LeakRefPtr.h"
+
+class nsThreadSyncDispatch : public mozilla::Runnable {
+ public:
+ nsThreadSyncDispatch(already_AddRefed<nsIEventTarget> aOrigin,
+ already_AddRefed<nsIRunnable>&& aTask)
+ : Runnable("nsThreadSyncDispatch"),
+ mOrigin(aOrigin),
+ mSyncTask(std::move(aTask)),
+ mIsPending(true) {}
+
+ bool IsPending() {
+ // This is an atomic acquire on the origin thread.
+ return mIsPending;
+ }
+
+ void SpinEventLoopUntilComplete(const nsACString& aVeryGoodReasonToDoThis) {
+ mozilla::SpinEventLoopUntil(aVeryGoodReasonToDoThis,
+ [&]() -> bool { return !IsPending(); });
+ }
+
+ private:
+ NS_IMETHOD Run() override {
+ if (nsCOMPtr<nsIRunnable> task = mSyncTask.take()) {
+ MOZ_ASSERT(!mSyncTask);
+
+ mozilla::DebugOnly<nsresult> result = task->Run();
+ MOZ_ASSERT(NS_SUCCEEDED(result), "task in sync dispatch should not fail");
+
+ // We must release the task here to ensure that when the original
+ // thread is unblocked, this task has been released.
+ task = nullptr;
+
+ // This is an atomic release on the target thread.
+ mIsPending = false;
+
+ // unblock the origin thread
+ mOrigin->Dispatch(this, NS_DISPATCH_IGNORE_BLOCK_DISPATCH);
+ }
+
+ return NS_OK;
+ }
+
+ nsCOMPtr<nsIEventTarget> mOrigin;
+ // The task is leaked by default when Run() is not called, because
+ // otherwise we may release it in an incorrect thread.
+ mozilla::LeakRefPtr<nsIRunnable> mSyncTask;
+ mozilla::Atomic<bool, mozilla::ReleaseAcquire> mIsPending;
+};
+
+#endif // nsThreadSyncDispatch_h_