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diff --git a/dom/workers/WorkerRunnable.h b/dom/workers/WorkerRunnable.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 mozilla_dom_workers_workerrunnable_h__
+#define mozilla_dom_workers_workerrunnable_h__
+
+#include <cstdint>
+#include <utility>
+#include "MainThreadUtils.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkerStatus.h"
+#include "nsCOMPtr.h"
+#include "nsICancelableRunnable.h"
+#include "nsIRunnable.h"
+#include "nsISupports.h"
+#include "nsStringFwd.h"
+#include "nsThreadUtils.h"
+#include "nscore.h"
+
+struct JSContext;
+class nsIEventTarget;
+class nsIGlobalObject;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class WorkerPrivate;
+
+// Use this runnable to communicate from the worker to its parent or vice-versa.
+// The busy count must be taken into consideration and declared at construction
+// time.
+class WorkerRunnable : public nsIRunnable, public nsICancelableRunnable {
+ public:
+  enum TargetAndBusyBehavior {
+    // Target the main thread for top-level workers, otherwise target the
+    // WorkerThread of the worker's parent. No change to the busy count.
+    ParentThreadUnchangedBusyCount,
+
+    // Target the thread where the worker event loop runs. The busy count will
+    // be incremented before dispatching and decremented (asynchronously) after
+    // running.
+    WorkerThreadModifyBusyCount,
+
+    // Target the thread where the worker event loop runs. The busy count will
+    // not be modified in any way. Besides worker-internal runnables this is
+    // almost always the wrong choice.
+    WorkerThreadUnchangedBusyCount
+  };
+
+ protected:
+  // The WorkerPrivate that this runnable is associated with.
+  WorkerPrivate* mWorkerPrivate;
+
+  // See above.
+  TargetAndBusyBehavior mBehavior;
+
+  // It's unclear whether or not Cancel() is supposed to work when called on any
+  // thread. To be safe we're using an atomic but it's likely overkill.
+  Atomic<uint32_t> mCanceled;
+
+ private:
+  // Whether or not Cancel() is currently being called from inside the Run()
+  // method. Avoids infinite recursion when a subclass calls Run() from inside
+  // Cancel(). Only checked and modified on the target thread.
+  bool mCallingCancelWithinRun;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  // If you override Cancel() then you'll need to either call the base class
+  // Cancel() method or override IsCanceled() so that the Run() method bails out
+  // appropriately.
+  // Cancel() should not be called more than once and we throw
+  // NS_ERROR_UNEXPECTED if it is. If you override it, ensure to call the base
+  // class method first and bail out on failure to avoid unexpected side
+  // effects.
+  nsresult Cancel() override;
+
+  // The return value is true if and only if both PreDispatch and
+  // DispatchInternal return true.
+  bool Dispatch();
+
+  // See above note about Cancel().
+  // TODO: Check if we can remove the possibility to override IsCanceled.
+  virtual bool IsCanceled() const { return mCanceled != 0; }
+
+  // True if this runnable is handled by running JavaScript in some global that
+  // could possibly be a debuggee, and thus needs to be deferred when the target
+  // is paused in the debugger, until the JavaScript invocation in progress has
+  // run to completion. Examples are MessageEventRunnable and
+  // ReportErrorRunnable. These runnables are segregated into separate
+  // ThrottledEventQueues, which the debugger pauses.
+  //
+  // Note that debugger runnables do not fall in this category, since we don't
+  // support debugging the debugger server at the moment.
+  virtual bool IsDebuggeeRunnable() const { return false; }
+
+  static WorkerRunnable* FromRunnable(nsIRunnable* aRunnable);
+
+ protected:
+  WorkerRunnable(WorkerPrivate* aWorkerPrivate,
+                 TargetAndBusyBehavior aBehavior = WorkerThreadModifyBusyCount)
+#ifdef DEBUG
+      ;
+#else
+      : mWorkerPrivate(aWorkerPrivate),
+        mBehavior(aBehavior),
+        mCanceled(0),
+        mCallingCancelWithinRun(false) {
+  }
+#endif
+
+  // This class is reference counted.
+  virtual ~WorkerRunnable() = default;
+
+  // Returns true if this runnable should be dispatched to the debugger queue,
+  // and false otherwise.
+  virtual bool IsDebuggerRunnable() const;
+
+  nsIGlobalObject* DefaultGlobalObject() const;
+
+  // By default asserts that Dispatch() is being called on the right thread
+  // (ParentThread if |mTarget| is WorkerThread, or WorkerThread otherwise).
+  // Also increments the busy count of |mWorkerPrivate| if targeting the
+  // WorkerThread.
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate);
+
+  // By default asserts that Dispatch() is being called on the right thread
+  // (ParentThread if |mTarget| is WorkerThread, or WorkerThread otherwise).
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult);
+
+  // May be implemented by subclasses if desired if they need to do some sort of
+  // setup before we try to set up our JSContext and compartment for real.
+  // Typically the only thing that should go in here is creation of the worker's
+  // global.
+  //
+  // If false is returned, WorkerRun will not be called at all.  PostRun will
+  // still be called, with false passed for aRunResult.
+  virtual bool PreRun(WorkerPrivate* aWorkerPrivate);
+
+  // Must be implemented by subclasses. Called on the target thread.  The return
+  // value will be passed to PostRun().  The JSContext passed in here comes from
+  // an AutoJSAPI (or AutoEntryScript) that we set up on the stack.  If
+  // mBehavior is ParentThreadUnchangedBusyCount, it is in the compartment of
+  // mWorkerPrivate's reflector (i.e. the worker object in the parent thread),
+  // unless that reflector is null, in which case it's in the compartment of the
+  // parent global (which is the compartment reflector would have been in), or
+  // in the null compartment if there is no parent global.  For other mBehavior
+  // values, we're running on the worker thread and aCx is in whatever
+  // compartment GetCurrentWorkerThreadJSContext() was in when
+  // nsIRunnable::Run() got called.  This is actually important for cases when a
+  // runnable spins a syncloop and wants everything that happens during the
+  // syncloop to happen in the compartment that runnable set up (which may, for
+  // example, be a debugger sandbox compartment!).  If aCx wasn't in a
+  // compartment to start with, aCx will be in either the debugger global's
+  // compartment or the worker's global's compartment depending on whether
+  // IsDebuggerRunnable() is true.
+  //
+  // Immediately after WorkerRun returns, the caller will assert that either it
+  // returns false or there is no exception pending on aCx.  Then it will report
+  // any pending exceptions on aCx.
+  virtual bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) = 0;
+
+  // By default asserts that Run() (and WorkerRun()) were called on the correct
+  // thread.  Also sends an asynchronous message to the ParentThread if the
+  // busy count was previously modified in PreDispatch().
+  //
+  // The aCx passed here is the same one as was passed to WorkerRun and is
+  // still in the same compartment.  PostRun implementations must NOT leave an
+  // exception on the JSContext and must not run script, because the incoming
+  // JSContext may be in the null compartment.
+  virtual void PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                       bool aRunResult);
+
+  virtual bool DispatchInternal();
+
+  // Calling Run() directly is not supported. Just call Dispatch() and
+  // WorkerRun() will be called on the correct thread automatically.
+  NS_DECL_NSIRUNNABLE
+};
+
+// This runnable is used to send a message to a worker debugger.
+class WorkerDebuggerRunnable : public WorkerRunnable {
+ protected:
+  explicit WorkerDebuggerRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerRunnable(aWorkerPrivate, WorkerThreadUnchangedBusyCount) {}
+
+  virtual ~WorkerDebuggerRunnable() = default;
+
+ private:
+  virtual bool IsDebuggerRunnable() const override { return true; }
+
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) final {
+    AssertIsOnMainThread();
+
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+};
+
+// This runnable is used to send a message directly to a worker's sync loop.
+class WorkerSyncRunnable : public WorkerRunnable {
+ protected:
+  nsCOMPtr<nsIEventTarget> mSyncLoopTarget;
+
+  // Passing null for aSyncLoopTarget is allowed and will result in the behavior
+  // of a normal WorkerRunnable.
+  WorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                     nsIEventTarget* aSyncLoopTarget);
+
+  WorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                     nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget);
+
+  virtual ~WorkerSyncRunnable();
+
+  virtual bool DispatchInternal() override;
+};
+
+// This runnable is identical to WorkerSyncRunnable except it is meant to be
+// created on and dispatched from the main thread only.  Its WorkerRun/PostRun
+// will run on the worker thread.
+class MainThreadWorkerSyncRunnable : public WorkerSyncRunnable {
+ protected:
+  // Passing null for aSyncLoopTarget is allowed and will result in the behavior
+  // of a normal WorkerRunnable.
+  MainThreadWorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                               nsIEventTarget* aSyncLoopTarget)
+      : WorkerSyncRunnable(aWorkerPrivate, aSyncLoopTarget) {
+    AssertIsOnMainThread();
+  }
+
+  MainThreadWorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                               nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget)
+      : WorkerSyncRunnable(aWorkerPrivate, std::move(aSyncLoopTarget)) {
+    AssertIsOnMainThread();
+  }
+
+  virtual ~MainThreadWorkerSyncRunnable() = default;
+
+ private:
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+};
+
+// This runnable is processed as soon as it is received by the worker,
+// potentially running before previously queued runnables and perhaps even with
+// other JS code executing on the stack. These runnables must not alter the
+// state of the JS runtime and should only twiddle state values. The busy count
+// is never modified.
+class WorkerControlRunnable : public WorkerRunnable {
+  friend class WorkerPrivate;
+
+ protected:
+  WorkerControlRunnable(WorkerPrivate* aWorkerPrivate,
+                        TargetAndBusyBehavior aBehavior)
+#ifdef DEBUG
+      ;
+#else
+      : WorkerRunnable(aWorkerPrivate, aBehavior) {
+  }
+#endif
+
+  virtual ~WorkerControlRunnable() = default;
+
+  nsresult Cancel() override;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(WorkerControlRunnable, WorkerRunnable)
+
+ private:
+  virtual bool DispatchInternal() override;
+
+  // Should only be called by WorkerPrivate::DoRunLoop.
+  using WorkerRunnable::Cancel;
+};
+
+// A convenience class for WorkerRunnables that are originated on the main
+// thread.
+class MainThreadWorkerRunnable : public WorkerRunnable {
+ protected:
+  explicit MainThreadWorkerRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerRunnable(aWorkerPrivate, WorkerThreadUnchangedBusyCount) {
+    AssertIsOnMainThread();
+  }
+
+  virtual ~MainThreadWorkerRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    AssertIsOnMainThread();
+  }
+};
+
+// A convenience class for WorkerControlRunnables that originate on the main
+// thread.
+class MainThreadWorkerControlRunnable : public WorkerControlRunnable {
+ protected:
+  explicit MainThreadWorkerControlRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate, WorkerThreadUnchangedBusyCount) {}
+
+  virtual ~MainThreadWorkerControlRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    AssertIsOnMainThread();
+  }
+};
+
+// A WorkerRunnable that should be dispatched from the worker to itself for
+// async tasks. This will increment the busy count PostDispatch() (only if
+// dispatch was successful) and decrement it in PostRun().
+//
+// Async tasks will almost always want to use this since
+// a WorkerSameThreadRunnable keeps the Worker from being GCed.
+class WorkerSameThreadRunnable : public WorkerRunnable {
+ protected:
+  explicit WorkerSameThreadRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerRunnable(aWorkerPrivate, WorkerThreadModifyBusyCount) {}
+
+  virtual ~WorkerSameThreadRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override;
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+
+  // We just delegate PostRun to WorkerRunnable, since it does exactly
+  // what we want.
+};
+
+// Base class for the runnable objects, which makes a synchronous call to
+// dispatch the tasks from the worker thread to the main thread.
+//
+// Note that the derived class must override MainThreadRun.
+class WorkerMainThreadRunnable : public Runnable {
+ protected:
+  WorkerPrivate* mWorkerPrivate;
+  nsCOMPtr<nsISerialEventTarget> mSyncLoopTarget;
+  const nsCString mTelemetryKey;
+
+  explicit WorkerMainThreadRunnable(WorkerPrivate* aWorkerPrivate,
+                                    const nsACString& aTelemetryKey);
+  ~WorkerMainThreadRunnable();
+
+  virtual bool MainThreadRun() = 0;
+
+ public:
+  // Dispatch the runnable to the main thread.  If dispatch to main thread
+  // fails, or if the worker is in a state equal or greater of aFailStatus, an
+  // error will be reported on aRv. Normally you want to use 'Canceling' for
+  // aFailStatus, except if you want an infallible runnable. In this case, use
+  // 'Killing'.
+  // In that case the error MUST be propagated out to script.
+  void Dispatch(WorkerStatus aFailStatus, ErrorResult& aRv);
+
+ private:
+  NS_IMETHOD Run() override;
+};
+
+// This runnable is an helper class for dispatching something from a worker
+// thread to the main-thread and back to the worker-thread. During this
+// operation, this class will keep the worker alive.
+// The purpose of RunBackOnWorkerThreadForCleanup() must be used, as the name
+// says, only to release resources, no JS has to be executed, no timers, or
+// other things. The reason of such limitations is that, in order to execute
+// this method in any condition (also when the worker is shutting down), a
+// Control Runnable is used, and, this could generate a reordering of existing
+// runnables.
+class WorkerProxyToMainThreadRunnable : public Runnable {
+ protected:
+  WorkerProxyToMainThreadRunnable();
+
+  virtual ~WorkerProxyToMainThreadRunnable();
+
+  // First this method is called on the main-thread.
+  virtual void RunOnMainThread(WorkerPrivate* aWorkerPrivate) = 0;
+
+  // After this second method is called on the worker-thread.
+  virtual void RunBackOnWorkerThreadForCleanup(
+      WorkerPrivate* aWorkerPrivate) = 0;
+
+ public:
+  bool Dispatch(WorkerPrivate* aWorkerPrivate);
+
+  virtual bool ForMessaging() const { return false; }
+
+ private:
+  NS_IMETHOD Run() override;
+
+  void PostDispatchOnMainThread();
+
+  void ReleaseWorker();
+
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+};
+
+// This runnable is used to stop a sync loop and it's meant to be used on the
+// main-thread only. As sync loops keep the busy count incremented as long as
+// they run this runnable does not modify the busy count
+// in any way.
+class MainThreadStopSyncLoopRunnable : public WorkerSyncRunnable {
+  nsresult mResult;
+
+ public:
+  // Passing null for aSyncLoopTarget is not allowed.
+  MainThreadStopSyncLoopRunnable(WorkerPrivate* aWorkerPrivate,
+                                 nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget,
+                                 nsresult aResult);
+
+  // By default StopSyncLoopRunnables cannot be canceled since they could leave
+  // a sync loop spinning forever.
+  nsresult Cancel() override;
+
+ protected:
+  virtual ~MainThreadStopSyncLoopRunnable() = default;
+
+ private:
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) final {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override;
+
+  bool DispatchInternal() final;
+};
+
+// Runnables handled by content JavaScript (MessageEventRunnable, JavaScript
+// error reports, and so on) must not be delivered while that content is in the
+// midst of being debugged; the debuggee must be allowed to complete its current
+// JavaScript invocation and return to its own event loop. Only then is it
+// prepared for messages sent from the worker.
+//
+// Runnables that need to be deferred in this way should inherit from this
+// class. They will be routed to mMainThreadDebuggeeEventTarget, which is paused
+// while the window is suspended, as it is whenever the debugger spins its
+// nested event loop. When the debugger leaves its nested event loop, it resumes
+// the window, so that mMainThreadDebuggeeEventTarget will resume delivering
+// runnables from the worker when control returns to the main event loop.
+//
+// When a page enters the bfcache, it freezes all its workers. Since a frozen
+// worker processes only control runnables, it doesn't take any special
+// consideration to prevent WorkerDebuggeeRunnables sent from child to parent
+// workers from running; they'll never run anyway. But WorkerDebuggeeRunnables
+// from a top-level frozen worker to its parent window must not be delivered
+// either, even as the main thread event loop continues to spin. Thus, freezing
+// a top-level worker also pauses mMainThreadDebuggeeEventTarget.
+class WorkerDebuggeeRunnable : public WorkerRunnable {
+ protected:
+  WorkerDebuggeeRunnable(
+      WorkerPrivate* aWorkerPrivate,
+      TargetAndBusyBehavior aBehavior = ParentThreadUnchangedBusyCount)
+      : WorkerRunnable(aWorkerPrivate, aBehavior) {}
+
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) override;
+
+ private:
+  // This override is deliberately private: it doesn't make sense to call it if
+  // we know statically that we are a WorkerDebuggeeRunnable.
+  bool IsDebuggeeRunnable() const override { return true; }
+
+  // Runnables sent upwards, to the content window or parent worker, must keep
+  // their sender alive until they are delivered: they check back with the
+  // sender in case it has been terminated after having dispatched the runnable
+  // (in which case it should not be acted upon); and runnables sent to content
+  // wait until delivery to determine the target window, since
+  // WorkerPrivate::GetWindow may only be used on the main thread.
+  //
+  // Runnables sent downwards, from content to a worker or from a worker to a
+  // child, keep the sender alive because they are WorkerThreadModifyBusyCount
+  // runnables, and so leave this null.
+  RefPtr<ThreadSafeWorkerRef> mSender;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_workerrunnable_h__