1 files changed, 155 insertions, 0 deletions
diff --git a/xpcom/base/nsMessageLoop.cpp b/xpcom/base/nsMessageLoop.cpp
new file mode 100644
index 0000000000..98e335a9fd
--- /dev/null
+++ b/xpcom/base/nsMessageLoop.cpp
@@ -0,0 +1,155 @@
+/* -*- 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 "nsMessageLoop.h"
+#include "mozilla/WeakPtr.h"
+#include "base/message_loop.h"
+#include "base/task.h"
+#include "nsINamed.h"
+#include "nsIRunnable.h"
+#include "nsITimer.h"
+#include "nsCOMPtr.h"
+#include "nsComponentManagerUtils.h"
+#include "nsThreadUtils.h"
+
+using namespace mozilla;
+
+namespace {
+
+/**
+ * This Task runs its nsIRunnable when Run() is called, or after
+ * aEnsureRunsAfterMS milliseconds have elapsed since the object was
+ * constructed.
+ *
+ * Note that the MessageLoop owns this object and will delete it after it calls
+ * Run().  Tread lightly.
+ */
+class MessageLoopIdleTask : public Runnable, public SupportsWeakPtr {
+ public:
+  MessageLoopIdleTask(nsIRunnable* aTask, uint32_t aEnsureRunsAfterMS);
+  NS_IMETHOD Run() override;
+
+ private:
+  nsresult Init(uint32_t aEnsureRunsAfterMS);
+
+  nsCOMPtr<nsIRunnable> mTask;
+  nsCOMPtr<nsITimer> mTimer;
+
+  virtual ~MessageLoopIdleTask() = default;
+};
+
+/**
+ * This timer callback calls MessageLoopIdleTask::Run() when its timer fires.
+ * (The timer can't call back into MessageLoopIdleTask directly since that's
+ * not a refcounted object; it's owned by the MessageLoop.)
+ *
+ * We keep a weak reference to the MessageLoopIdleTask, although a raw pointer
+ * should in theory suffice: When the MessageLoopIdleTask runs (right before
+ * the MessageLoop deletes it), it cancels its timer.  But the weak pointer
+ * saves us from worrying about an edge case somehow messing us up here.
+ */
+class MessageLoopTimerCallback : public nsITimerCallback, public nsINamed {
+ public:
+  explicit MessageLoopTimerCallback(MessageLoopIdleTask* aTask);
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSITIMERCALLBACK
+
+  NS_IMETHOD GetName(nsACString& aName) override {
+    aName.AssignLiteral("MessageLoopTimerCallback");
+    return NS_OK;
+  }
+
+ private:
+  WeakPtr<MessageLoopIdleTask> mTask;
+
+  virtual ~MessageLoopTimerCallback() = default;
+};
+
+MessageLoopIdleTask::MessageLoopIdleTask(nsIRunnable* aTask,
+                                         uint32_t aEnsureRunsAfterMS)
+    : mozilla::Runnable("MessageLoopIdleTask"), mTask(aTask) {
+  // Init() really shouldn't fail, but if it does, we schedule our runnable
+  // immediately, because it's more important to guarantee that we run the task
+  // eventually than it is to run the task when we're idle.
+  nsresult rv = Init(aEnsureRunsAfterMS);
+  if (NS_FAILED(rv)) {
+    NS_WARNING(
+        "Running idle task early because we couldn't initialize our timer.");
+    NS_DispatchToCurrentThread(mTask);
+
+    mTask = nullptr;
+    mTimer = nullptr;
+  }
+}
+
+nsresult MessageLoopIdleTask::Init(uint32_t aEnsureRunsAfterMS) {
+  RefPtr<MessageLoopTimerCallback> callback =
+      new MessageLoopTimerCallback(this);
+  return NS_NewTimerWithCallback(getter_AddRefs(mTimer), callback,
+                                 aEnsureRunsAfterMS, nsITimer::TYPE_ONE_SHOT);
+}
+
+NS_IMETHODIMP
+MessageLoopIdleTask::Run() {
+  // Null out our pointers because if Run() was called by the timer, this
+  // object will be kept alive by the MessageLoop until the MessageLoop calls
+  // Run().
+
+  if (mTimer) {
+    mTimer->Cancel();
+    mTimer = nullptr;
+  }
+
+  if (mTask) {
+    mTask->Run();
+    mTask = nullptr;
+  }
+
+  return NS_OK;
+}
+
+MessageLoopTimerCallback::MessageLoopTimerCallback(MessageLoopIdleTask* aTask)
+    : mTask(aTask) {}
+
+NS_IMETHODIMP
+MessageLoopTimerCallback::Notify(nsITimer* aTimer) {
+  // We don't expect to hit the case when the timer fires but mTask has been
+  // deleted, because mTask should cancel the timer before the mTask is
+  // deleted.  But you never know...
+  NS_WARNING_ASSERTION(mTask, "This timer shouldn't have fired.");
+
+  if (mTask) {
+    mTask->Run();
+  }
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(MessageLoopTimerCallback, nsITimerCallback, nsINamed)
+
+}  // namespace
+
+NS_IMPL_ISUPPORTS(nsMessageLoop, nsIMessageLoop)
+
+NS_IMETHODIMP
+nsMessageLoop::PostIdleTask(nsIRunnable* aTask, uint32_t aEnsureRunsAfterMS) {
+  // The message loop owns MessageLoopIdleTask and deletes it after calling
+  // Run().  Be careful...
+  RefPtr<MessageLoopIdleTask> idle =
+      new MessageLoopIdleTask(aTask, aEnsureRunsAfterMS);
+  MessageLoop::current()->PostIdleTask(idle.forget());
+
+  return NS_OK;
+}
+
+nsresult nsMessageLoopConstructor(nsISupports* aOuter, const nsIID& aIID,
+                                  void** aInstancePtr) {
+  if (NS_WARN_IF(aOuter)) {
+    return NS_ERROR_NO_AGGREGATION;
+  }
+  nsISupports* messageLoop = new nsMessageLoop();
+  return messageLoop->QueryInterface(aIID, aInstancePtr);
+}