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-rw-r--r--xpcom/threads/SyncRunnable.h157
1 files changed, 157 insertions, 0 deletions
diff --git a/xpcom/threads/SyncRunnable.h b/xpcom/threads/SyncRunnable.h
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+++ b/xpcom/threads/SyncRunnable.h
@@ -0,0 +1,157 @@
+/* -*- 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 mozilla_SyncRunnable_h
+#define mozilla_SyncRunnable_h
+
+#include <utility>
+
+#include "mozilla/AbstractThread.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/dom/JSExecutionManager.h"
+#include "nsThreadUtils.h"
+
+namespace mozilla {
+
+/**
+ * This class will wrap a nsIRunnable and dispatch it to the target thread
+ * synchronously. This is different from
+ * NS_DispatchAndSpinEventLoopUntilComplete: this class does not spin the event
+ * loop waiting for the event to be dispatched. This means that you don't risk
+ * reentrance from pending messages, but you must be sure that the target thread
+ * does not ever block on this thread, or else you will deadlock.
+ *
+ * Typical usage:
+ * RefPtr<SyncRunnable> sr = new SyncRunnable(new myrunnable...());
+ * sr->DispatchToThread(t);
+ *
+ * We also provide convenience wrappers:
+ * SyncRunnable::DispatchToThread(pThread, new myrunnable...());
+ * SyncRunnable::DispatchToThread(pThread, NS_NewRunnableFunction(...));
+ *
+ */
+class SyncRunnable : public Runnable {
+ public:
+ explicit SyncRunnable(nsIRunnable* aRunnable)
+ : Runnable("SyncRunnable"),
+ mRunnable(aRunnable),
+ mMonitor("SyncRunnable"),
+ mDone(false) {}
+
+ explicit SyncRunnable(already_AddRefed<nsIRunnable> aRunnable)
+ : Runnable("SyncRunnable"),
+ mRunnable(std::move(aRunnable)),
+ mMonitor("SyncRunnable"),
+ mDone(false) {}
+
+ nsresult DispatchToThread(nsIEventTarget* aThread,
+ bool aForceDispatch = false) {
+ nsresult rv;
+ bool on;
+
+ if (!aForceDispatch) {
+ rv = aThread->IsOnCurrentThread(&on);
+ MOZ_ASSERT(NS_SUCCEEDED(rv));
+ if (NS_SUCCEEDED(rv) && on) {
+ mRunnable->Run();
+ return NS_OK;
+ }
+ }
+
+ rv = aThread->Dispatch(this, NS_DISPATCH_NORMAL);
+ if (NS_SUCCEEDED(rv)) {
+ mozilla::MonitorAutoLock lock(mMonitor);
+ // This could be synchronously dispatching to a thread currently waiting
+ // for JS execution clearance. Yield JS execution.
+ dom::AutoYieldJSThreadExecution yield;
+
+ while (!mDone) {
+ lock.Wait();
+ }
+ }
+ return rv;
+ }
+
+ nsresult DispatchToThread(AbstractThread* aThread,
+ bool aForceDispatch = false) {
+ if (!aForceDispatch && aThread->IsCurrentThreadIn()) {
+ mRunnable->Run();
+ return NS_OK;
+ }
+
+ // Check we don't have tail dispatching here. Otherwise we will deadlock
+ // ourself when spinning the loop below.
+ MOZ_ASSERT(!aThread->RequiresTailDispatchFromCurrentThread());
+
+ nsresult rv = aThread->Dispatch(RefPtr<nsIRunnable>(this).forget());
+ if (NS_SUCCEEDED(rv)) {
+ mozilla::MonitorAutoLock lock(mMonitor);
+ while (!mDone) {
+ lock.Wait();
+ }
+ }
+ return rv;
+ }
+
+ static nsresult DispatchToThread(nsIEventTarget* aThread,
+ nsIRunnable* aRunnable,
+ bool aForceDispatch = false) {
+ RefPtr<SyncRunnable> s(new SyncRunnable(aRunnable));
+ return s->DispatchToThread(aThread, aForceDispatch);
+ }
+
+ static nsresult DispatchToThread(AbstractThread* aThread,
+ nsIRunnable* aRunnable,
+ bool aForceDispatch = false) {
+ RefPtr<SyncRunnable> s(new SyncRunnable(aRunnable));
+ return s->DispatchToThread(aThread, aForceDispatch);
+ }
+
+ static nsresult DispatchToThread(nsIEventTarget* aThread,
+ already_AddRefed<nsIRunnable> aRunnable,
+ bool aForceDispatch = false) {
+ RefPtr<SyncRunnable> s(new SyncRunnable(std::move(aRunnable)));
+ return s->DispatchToThread(aThread, aForceDispatch);
+ }
+
+ static nsresult DispatchToThread(AbstractThread* aThread,
+ already_AddRefed<nsIRunnable> aRunnable,
+ bool aForceDispatch = false) {
+ RefPtr<SyncRunnable> s(new SyncRunnable(std::move(aRunnable)));
+ return s->DispatchToThread(aThread, aForceDispatch);
+ }
+
+ // These deleted overloads prevent accidentally (if harmlessly) double-
+ // wrapping SyncRunnable, which was previously a common anti-pattern.
+ static nsresult DispatchToThread(nsIEventTarget* aThread,
+ SyncRunnable* aRunnable,
+ bool aForceDispatch = false) = delete;
+ static nsresult DispatchToThread(AbstractThread* aThread,
+ SyncRunnable* aRunnable,
+ bool aForceDispatch = false) = delete;
+
+ protected:
+ NS_IMETHOD Run() override {
+ mRunnable->Run();
+
+ mozilla::MonitorAutoLock lock(mMonitor);
+ MOZ_ASSERT(!mDone);
+
+ mDone = true;
+ mMonitor.Notify();
+
+ return NS_OK;
+ }
+
+ private:
+ nsCOMPtr<nsIRunnable> mRunnable;
+ mozilla::Monitor mMonitor;
+ bool mDone MOZ_GUARDED_BY(mMonitor);
+};
+
+} // namespace mozilla
+
+#endif // mozilla_SyncRunnable_h