1 files changed, 192 insertions, 0 deletions
diff --git a/xpcom/threads/AbstractThread.cpp b/xpcom/threads/AbstractThread.cpp
new file mode 100644
index 000000000..451b317d8
--- /dev/null
+++ b/xpcom/threads/AbstractThread.cpp
@@ -0,0 +1,192 @@
+/* -*- 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/. */
+
+#include "mozilla/AbstractThread.h"
+
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MozPromise.h" // We initialize the MozPromise logging in this file.
+#include "mozilla/StaticPtr.h"
+#include "mozilla/StateWatching.h" // We initialize the StateWatching logging in this file.
+#include "mozilla/TaskQueue.h"
+#include "mozilla/TaskDispatcher.h"
+#include "mozilla/Unused.h"
+
+#include "nsThreadUtils.h"
+#include "nsContentUtils.h"
+#include "nsServiceManagerUtils.h"
+
+
+namespace mozilla {
+
+LazyLogModule gMozPromiseLog("MozPromise");
+LazyLogModule gStateWatchingLog("StateWatching");
+
+StaticRefPtr<AbstractThread> sMainThread;
+MOZ_THREAD_LOCAL(AbstractThread*) AbstractThread::sCurrentThreadTLS;
+
+class XPCOMThreadWrapper : public AbstractThread
+{
+public:
+  explicit XPCOMThreadWrapper(nsIThread* aTarget, bool aRequireTailDispatch)
+    : AbstractThread(aRequireTailDispatch)
+    , mTarget(aTarget)
+  {
+    // Our current mechanism of implementing tail dispatch is appshell-specific.
+    // This is because a very similar mechanism already exists on the main
+    // thread, and we want to avoid making event dispatch on the main thread
+    // more complicated than it already is.
+    //
+    // If you need to use tail dispatch on other XPCOM threads, you'll need to
+    // implement an nsIThreadObserver to fire the tail dispatcher at the
+    // appropriate times.
+    MOZ_ASSERT_IF(aRequireTailDispatch,
+                  NS_IsMainThread() && NS_GetCurrentThread() == aTarget);
+  }
+
+  virtual void Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                        DispatchFailureHandling aFailureHandling = AssertDispatchSuccess,
+                        DispatchReason aReason = NormalDispatch) override
+  {
+    nsCOMPtr<nsIRunnable> r = aRunnable;
+    AbstractThread* currentThread;
+    if (aReason != TailDispatch && (currentThread = GetCurrent()) && RequiresTailDispatch(currentThread)) {
+      currentThread->TailDispatcher().AddTask(this, r.forget(), aFailureHandling);
+      return;
+    }
+
+    nsresult rv = mTarget->Dispatch(r, NS_DISPATCH_NORMAL);
+    MOZ_DIAGNOSTIC_ASSERT(aFailureHandling == DontAssertDispatchSuccess || NS_SUCCEEDED(rv));
+    Unused << rv;
+  }
+
+  virtual bool IsCurrentThreadIn() override
+  {
+    // Compare NSPR threads so that this works after shutdown when
+    // NS_GetCurrentThread starts returning null.
+    PRThread* thread = nullptr;
+    mTarget->GetPRThread(&thread);
+    bool in = PR_GetCurrentThread() == thread;
+    return in;
+  }
+
+  void FireTailDispatcher()
+  {
+    MOZ_DIAGNOSTIC_ASSERT(mTailDispatcher.isSome());
+    mTailDispatcher.ref().DrainDirectTasks();
+    mTailDispatcher.reset();
+  }
+
+  virtual TaskDispatcher& TailDispatcher() override
+  {
+    MOZ_ASSERT(this == sMainThread); // See the comment in the constructor.
+    MOZ_ASSERT(IsCurrentThreadIn());
+    if (!mTailDispatcher.isSome()) {
+      mTailDispatcher.emplace(/* aIsTailDispatcher = */ true);
+
+      nsCOMPtr<nsIRunnable> event = NewRunnableMethod(this, &XPCOMThreadWrapper::FireTailDispatcher);
+      nsContentUtils::RunInStableState(event.forget());
+    }
+
+    return mTailDispatcher.ref();
+  }
+
+  virtual bool MightHaveTailTasks() override
+  {
+    return mTailDispatcher.isSome();
+  }
+
+  virtual nsIThread* AsXPCOMThread() override { return mTarget; }
+
+private:
+  RefPtr<nsIThread> mTarget;
+  Maybe<AutoTaskDispatcher> mTailDispatcher;
+};
+
+void
+AbstractThread::TailDispatchTasksFor(AbstractThread* aThread)
+{
+  if (MightHaveTailTasks()) {
+    TailDispatcher().DispatchTasksFor(aThread);
+  }
+}
+
+bool
+AbstractThread::HasTailTasksFor(AbstractThread* aThread)
+{
+  if (!MightHaveTailTasks()) {
+    return false;
+  }
+  return TailDispatcher().HasTasksFor(aThread);
+}
+
+bool
+AbstractThread::RequiresTailDispatch(AbstractThread* aThread) const
+{
+  MOZ_ASSERT(aThread);
+  // We require tail dispatch if both the source and destination
+  // threads support it.
+  return SupportsTailDispatch() && aThread->SupportsTailDispatch();
+}
+
+bool
+AbstractThread::RequiresTailDispatchFromCurrentThread() const
+{
+  AbstractThread* current = GetCurrent();
+  return current && RequiresTailDispatch(current);
+}
+
+AbstractThread*
+AbstractThread::MainThread()
+{
+  MOZ_ASSERT(sMainThread);
+  return sMainThread;
+}
+
+void
+AbstractThread::InitStatics()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(!sMainThread);
+  nsCOMPtr<nsIThread> mainThread;
+  NS_GetMainThread(getter_AddRefs(mainThread));
+  MOZ_DIAGNOSTIC_ASSERT(mainThread);
+  sMainThread = new XPCOMThreadWrapper(mainThread.get(), /* aRequireTailDispatch = */ true);
+  ClearOnShutdown(&sMainThread);
+
+  if (!sCurrentThreadTLS.init()) {
+    MOZ_CRASH();
+  }
+  sCurrentThreadTLS.set(sMainThread);
+}
+
+void
+AbstractThread::DispatchStateChange(already_AddRefed<nsIRunnable> aRunnable)
+{
+  GetCurrent()->TailDispatcher().AddStateChangeTask(this, Move(aRunnable));
+}
+
+/* static */ void
+AbstractThread::DispatchDirectTask(already_AddRefed<nsIRunnable> aRunnable)
+{
+  GetCurrent()->TailDispatcher().AddDirectTask(Move(aRunnable));
+}
+
+/* static */
+already_AddRefed<AbstractThread>
+AbstractThread::CreateXPCOMThreadWrapper(nsIThread* aThread, bool aRequireTailDispatch)
+{
+  RefPtr<XPCOMThreadWrapper> wrapper = new XPCOMThreadWrapper(aThread, aRequireTailDispatch);
+  // Set the thread-local sCurrentThreadTLS to point to the wrapper on the
+  // target thread. This ensures that sCurrentThreadTLS is as expected by
+  // AbstractThread::GetCurrent() on the target thread.
+  nsCOMPtr<nsIRunnable> r =
+    NS_NewRunnableFunction([wrapper]() { sCurrentThreadTLS.set(wrapper); });
+  aThread->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+  return wrapper.forget();
+}
+
+} // namespace mozilla