Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1399 insertions, 0 deletions

diff --git a/dom/ipc/ProcessHangMonitor.cpp b/dom/ipc/ProcessHangMonitor.cpp
new file mode 100644
index 0000000000..1dcba24406
--- /dev/null
+++ b/dom/ipc/ProcessHangMonitor.cpp
@@ -0,0 +1,1399 @@
+/* -*- 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/ProcessHangMonitor.h"
+#include "mozilla/ProcessHangMonitorIPC.h"
+
+#include "jsapi.h"
+#include "xpcprivate.h"
+
+#include "mozilla/Atomics.h"
+#include "mozilla/BackgroundHangMonitor.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/dom/CancelContentJSOptionsBinding.h"
+#include "mozilla/dom/CanonicalBrowsingContext.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/Element.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/dom/BrowserParent.h"
+#include "mozilla/ipc/Endpoint.h"
+#include "mozilla/ipc/ProcessChild.h"
+#include "mozilla/ipc/TaskFactory.h"
+#include "mozilla/Monitor.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/StaticMonitor.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/WeakPtr.h"
+
+#include "MainThreadUtils.h"
+#include "nsExceptionHandler.h"
+#include "nsFrameLoader.h"
+#include "nsIHangReport.h"
+#include "nsIRemoteTab.h"
+#include "nsNetUtil.h"
+#include "nsQueryObject.h"
+#include "nsThreadUtils.h"
+
+#include "base/task.h"
+#include "base/thread.h"
+
+#ifdef XP_WIN
+// For IsDebuggerPresent()
+#  include <windows.h>
+#endif
+
+#ifdef XP_MACOSX
+// for qos controls
+#  include <sys/qos.h>
+#endif
+
+using namespace mozilla;
+using namespace mozilla::dom;
+using namespace mozilla::ipc;
+
+/*
+ * Basic architecture:
+ *
+ * Each process has its own ProcessHangMonitor singleton. This singleton exists
+ * as long as there is at least one content process in the system. Each content
+ * process has a HangMonitorChild and the chrome process has one
+ * HangMonitorParent per process. Each process (including the chrome process)
+ * runs a hang monitoring thread. The PHangMonitor actors are bound to this
+ * thread so that they never block on the main thread.
+ *
+ * When the content process detects a hang, it posts a task to its hang thread,
+ * which sends an IPC message to the hang thread in the parent. The parent
+ * cancels any ongoing CPOW requests and then posts a runnable to the main
+ * thread that notifies Firefox frontend code of the hang. The frontend code is
+ * passed an nsIHangReport, which can be used to terminate the hang.
+ *
+ * If the user chooses to terminate a script, a task is posted to the chrome
+ * process's hang monitoring thread, which sends an IPC message to the hang
+ * thread in the content process. That thread sets a flag to indicate that JS
+ * execution should be terminated the next time it hits the interrupt
+ * callback. A similar scheme is used for debugging slow scripts. If a content
+ * process or plug-in needs to be terminated, the chrome process does so
+ * directly, without messaging the content process.
+ */
+
+namespace {
+
+/* Child process objects */
+
+class HangMonitorChild : public PProcessHangMonitorChild,
+                         public BackgroundHangAnnotator {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_MAIN_THREAD(
+      HangMonitorChild, override)
+
+  void Bind(Endpoint<PProcessHangMonitorChild>&& aEndpoint);
+
+  using SlowScriptAction = ProcessHangMonitor::SlowScriptAction;
+  SlowScriptAction NotifySlowScript(nsIBrowserChild* aBrowserChild,
+                                    const char* aFileName,
+                                    const nsString& aAddonId,
+                                    const double aDuration);
+  void NotifySlowScriptAsync(TabId aTabId, const nsCString& aFileName,
+                             const nsString& aAddonId, const double aDuration);
+
+  bool IsDebuggerStartupComplete();
+
+  void ClearHang();
+  void ClearHangAsync();
+  void ClearPaintWhileInterruptingJS();
+
+  // MaybeStartPaintWhileInterruptingJS will notify the background hang monitor
+  // of activity if this is the first time calling it since
+  // ClearPaintWhileInterruptingJS. It should be callable from any thread, but
+  // you must be holding mMonitor if using it off the main thread, since it
+  // could race with ClearPaintWhileInterruptingJS.
+  void MaybeStartPaintWhileInterruptingJS();
+
+  mozilla::ipc::IPCResult RecvTerminateScript() override;
+  mozilla::ipc::IPCResult RecvRequestContentJSInterrupt() override;
+  mozilla::ipc::IPCResult RecvBeginStartingDebugger() override;
+  mozilla::ipc::IPCResult RecvEndStartingDebugger() override;
+
+  mozilla::ipc::IPCResult RecvPaintWhileInterruptingJS(
+      const TabId& aTabId) override;
+
+  mozilla::ipc::IPCResult RecvUnloadLayersWhileInterruptingJS(
+      const TabId& aTabId) override;
+
+  mozilla::ipc::IPCResult RecvCancelContentJSExecutionIfRunning(
+      const TabId& aTabId, const nsIRemoteTab::NavigationType& aNavigationType,
+      const int32_t& aNavigationIndex,
+      const mozilla::Maybe<nsCString>& aNavigationURI,
+      const int32_t& aEpoch) override;
+
+  mozilla::ipc::IPCResult RecvSetMainThreadQoSPriority(
+      const nsIThread::QoSPriority& aQoSPriority) override;
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  bool InterruptCallback();
+  void Shutdown();
+
+  static HangMonitorChild* Get() MOZ_REQUIRES(sMainThreadCapability) {
+    return sInstance;
+  }
+
+  static void CreateAndBind(ProcessHangMonitor* aMonitor,
+                            Endpoint<PProcessHangMonitorChild>&& aEndpoint);
+
+  void Dispatch(already_AddRefed<nsIRunnable> aRunnable) {
+    mHangMonitor->Dispatch(std::move(aRunnable));
+  }
+  bool IsOnThread() { return mHangMonitor->IsOnThread(); }
+
+  void AnnotateHang(BackgroundHangAnnotations& aAnnotations) override;
+
+ protected:
+  friend class mozilla::ProcessHangMonitor;
+
+ private:
+  explicit HangMonitorChild(ProcessHangMonitor* aMonitor);
+  ~HangMonitorChild() override;
+
+  void ShutdownOnThread();
+
+  static StaticRefPtr<HangMonitorChild> sInstance
+      MOZ_GUARDED_BY(sMainThreadCapability);
+
+  const RefPtr<ProcessHangMonitor> mHangMonitor;
+
+#ifdef XP_MACOSX
+  // On macOS, the pthread_t is required to start a QoS class override. As we
+  // can't recover this from a PRThread*, we need to record it when the
+  // HangMonitorChild is initially created on the main thread.
+  const pthread_t mMainPThread;
+#endif
+
+  Monitor mMonitor;
+
+  // Main thread-only.
+  bool mSentReport;
+
+  // These fields must be accessed with mMonitor held.
+  bool mTerminateScript MOZ_GUARDED_BY(mMonitor);
+  bool mStartDebugger MOZ_GUARDED_BY(mMonitor);
+  bool mFinishedStartingDebugger MOZ_GUARDED_BY(mMonitor);
+
+  // this variable is used to paint/unload layers
+  // if not set, no action required
+  // true means, we will paint. false - unload layers
+  Maybe<bool> mPaintWhileInterruptingJS MOZ_GUARDED_BY(mMonitor);
+  TabId mPaintWhileInterruptingJSTab MOZ_GUARDED_BY(mMonitor);
+  bool mCancelContentJS MOZ_GUARDED_BY(mMonitor);
+  TabId mCancelContentJSTab MOZ_GUARDED_BY(mMonitor);
+  nsIRemoteTab::NavigationType mCancelContentJSNavigationType
+      MOZ_GUARDED_BY(mMonitor);
+  int32_t mCancelContentJSNavigationIndex MOZ_GUARDED_BY(mMonitor);
+  mozilla::Maybe<nsCString> mCancelContentJSNavigationURI
+      MOZ_GUARDED_BY(mMonitor);
+  int32_t mCancelContentJSEpoch MOZ_GUARDED_BY(mMonitor);
+  bool mShutdownDone MOZ_GUARDED_BY(mMonitor);
+
+  JSContext* mContext;  // const after constructor
+
+  // This field is only accessed on the hang thread.
+  bool mIPCOpen;
+
+  // Allows us to ensure we NotifyActivity only once, allowing
+  // either thread to do so.
+  Atomic<bool> mPaintWhileInterruptingJSActive;
+};
+
+StaticRefPtr<HangMonitorChild> HangMonitorChild::sInstance;
+
+/* Parent process objects */
+
+class HangMonitorParent;
+
+class HangMonitoredProcess final : public nsIHangReport {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  HangMonitoredProcess(HangMonitorParent* aActor, ContentParent* aContentParent)
+      : mActor(aActor), mContentParent(aContentParent) {}
+
+  NS_DECL_NSIHANGREPORT
+
+  // Called when a content process shuts down.
+  void Clear() {
+    mContentParent = nullptr;
+    mActor = nullptr;
+  }
+
+  /**
+   * Sets the information associated with this hang: this includes the tab ID,
+   * filename, duration, and an add-on ID if it was caused by an add-on.
+   *
+   * @param aDumpId The ID of a minidump taken when the hang occurred
+   */
+  void SetSlowScriptData(const SlowScriptData& aSlowScriptData,
+                         const nsAString& aDumpId) {
+    mSlowScriptData = aSlowScriptData;
+    mDumpId = aDumpId;
+  }
+
+  void ClearHang() {
+    mSlowScriptData = SlowScriptData();
+    mDumpId.Truncate();
+  }
+
+ private:
+  ~HangMonitoredProcess() = default;
+
+  // Everything here is main thread-only.
+  HangMonitorParent* mActor;
+  ContentParent* mContentParent;
+  SlowScriptData mSlowScriptData;
+  nsAutoString mDumpId;
+};
+
+class HangMonitorParent : public PProcessHangMonitorParent {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING_WITH_DELETE_ON_MAIN_THREAD(
+      HangMonitorParent, override)
+
+  explicit HangMonitorParent(ProcessHangMonitor* aMonitor);
+
+  void Bind(Endpoint<PProcessHangMonitorParent>&& aEndpoint);
+
+  mozilla::ipc::IPCResult RecvHangEvidence(
+      const SlowScriptData& aSlowScriptData) override;
+  mozilla::ipc::IPCResult RecvClearHang() override;
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  void SetProcess(HangMonitoredProcess* aProcess) { mProcess = aProcess; }
+
+  void Shutdown();
+
+  void PaintWhileInterruptingJS(dom::BrowserParent* aTab);
+
+  void UnloadLayersWhileInterruptingJS(dom::BrowserParent* aTab);
+  void CancelContentJSExecutionIfRunning(
+      dom::BrowserParent* aBrowserParent,
+      nsIRemoteTab::NavigationType aNavigationType,
+      const dom::CancelContentJSOptions& aCancelContentJSOptions);
+
+  void SetMainThreadQoSPriority(nsIThread::QoSPriority aQoSPriority);
+
+  void TerminateScript();
+  void BeginStartingDebugger();
+  void EndStartingDebugger();
+
+  nsresult Dispatch(already_AddRefed<nsIRunnable> aRunnable) {
+    return mHangMonitor->Dispatch(std::move(aRunnable));
+  }
+  bool IsOnThread() { return mHangMonitor->IsOnThread(); }
+
+ private:
+  ~HangMonitorParent() override = default;
+
+  void SendHangNotification(const SlowScriptData& aSlowScriptData,
+                            const nsString& aBrowserDumpId);
+
+  void ClearHangNotification();
+
+  void PaintOrUnloadLayersWhileInterruptingJSOnThread(bool aPaint,
+                                                      TabId aTabId);
+  void CancelContentJSExecutionIfRunningOnThread(
+      TabId aTabId, nsIRemoteTab::NavigationType aNavigationType,
+      int32_t aNavigationIndex, nsIURI* aNavigationURI, int32_t aEpoch);
+
+#ifdef XP_MACOSX
+  void SetMainThreadQoSPriorityOnThread(nsIThread::QoSPriority aQoSPriority);
+#endif
+
+  void ShutdownOnThread();
+
+  const RefPtr<ProcessHangMonitor> mHangMonitor;
+
+  // This field is only accessed on the hang thread.
+  bool mIPCOpen;
+
+  Monitor mMonitor;
+
+  // MainThread only
+  RefPtr<HangMonitoredProcess> mProcess;
+
+  // Must be accessed with mMonitor held.
+  bool mShutdownDone MOZ_GUARDED_BY(mMonitor);
+  mozilla::ipc::TaskFactory<HangMonitorParent> mMainThreadTaskFactory
+      MOZ_GUARDED_BY(mMonitor);
+};
+
+}  // namespace
+
+/* HangMonitorChild implementation */
+
+HangMonitorChild::HangMonitorChild(ProcessHangMonitor* aMonitor)
+    : mHangMonitor(aMonitor),
+#ifdef XP_MACOSX
+      mMainPThread(pthread_self()),
+#endif
+      mMonitor("HangMonitorChild lock"),
+      mSentReport(false),
+      mTerminateScript(false),
+      mStartDebugger(false),
+      mFinishedStartingDebugger(false),
+      mCancelContentJS(false),
+      mCancelContentJSNavigationType(nsIRemoteTab::NAVIGATE_BACK),
+      mCancelContentJSNavigationIndex(0),
+      mCancelContentJSEpoch(0),
+      mShutdownDone(false),
+      mIPCOpen(true),
+      mPaintWhileInterruptingJSActive(false) {
+  ReleaseAssertIsOnMainThread();
+  MOZ_ASSERT(!sInstance);
+
+  mContext = danger::GetJSContext();
+}
+
+HangMonitorChild::~HangMonitorChild() {
+  ReleaseAssertIsOnMainThread();
+  MOZ_ASSERT(sInstance != this);
+}
+
+void HangMonitorChild::CreateAndBind(
+    ProcessHangMonitor* aMonitor,
+    Endpoint<PProcessHangMonitorChild>&& aEndpoint) {
+  ReleaseAssertIsOnMainThread();
+  MOZ_ASSERT(!sInstance);
+
+  sInstance = new HangMonitorChild(aMonitor);
+
+  BackgroundHangMonitor::RegisterAnnotator(*sInstance);
+
+  aMonitor->Dispatch(NewRunnableMethod<Endpoint<PProcessHangMonitorChild>&&>(
+      "HangMonitorChild::Bind", sInstance.get(), &HangMonitorChild::Bind,
+      std::move(aEndpoint)));
+}
+
+bool HangMonitorChild::InterruptCallback() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  if (StaticPrefs::dom_abort_script_on_child_shutdown() &&
+      mozilla::ipc::ProcessChild::ExpectingShutdown()) {
+    // We preserve chrome JS from cancel, but not extension content JS.
+    if (!nsContentUtils::IsCallerChrome()) {
+      NS_WARNING(
+          "HangMonitorChild::InterruptCallback: ExpectingShutdown, "
+          "canceling content JS execution.\n");
+      return false;
+    }
+    return true;
+  }
+
+  // Don't start painting if we're not in a good place to run script. We run
+  // chrome script during layout and such, and it wouldn't be good to interrupt
+  // painting code from there.
+  if (!nsContentUtils::IsSafeToRunScript()) {
+    return true;
+  }
+
+  Maybe<bool> paintWhileInterruptingJS;
+  TabId paintWhileInterruptingJSTab;
+
+  {
+    MonitorAutoLock lock(mMonitor);
+    paintWhileInterruptingJS = mPaintWhileInterruptingJS;
+    paintWhileInterruptingJSTab = mPaintWhileInterruptingJSTab;
+
+    mPaintWhileInterruptingJS.reset();
+  }
+
+  if (paintWhileInterruptingJS.isSome()) {
+    RefPtr<BrowserChild> browserChild =
+        BrowserChild::FindBrowserChild(paintWhileInterruptingJSTab);
+    if (browserChild) {
+      js::AutoAssertNoContentJS nojs(mContext);
+      if (paintWhileInterruptingJS.value()) {
+        browserChild->PaintWhileInterruptingJS();
+      } else {
+        browserChild->UnloadLayersWhileInterruptingJS();
+      }
+    }
+  }
+
+  // Only handle the interrupt for cancelling content JS if we have a
+  // non-privileged script (i.e. not part of Gecko or an add-on).
+  JS::Rooted<JSObject*> global(mContext, JS::CurrentGlobalOrNull(mContext));
+  nsIPrincipal* principal = xpc::GetObjectPrincipal(global);
+  if (principal && (principal->IsSystemPrincipal() ||
+                    principal->GetIsAddonOrExpandedAddonPrincipal())) {
+    return true;
+  }
+
+  nsCOMPtr<nsPIDOMWindowInner> win = xpc::WindowOrNull(global);
+  if (!win) {
+    return true;
+  }
+
+  bool cancelContentJS;
+  TabId cancelContentJSTab;
+  nsIRemoteTab::NavigationType cancelContentJSNavigationType;
+  int32_t cancelContentJSNavigationIndex;
+  mozilla::Maybe<nsCString> cancelContentJSNavigationURI;
+  int32_t cancelContentJSEpoch;
+
+  {
+    MonitorAutoLock lock(mMonitor);
+    cancelContentJS = mCancelContentJS;
+    cancelContentJSTab = mCancelContentJSTab;
+    cancelContentJSNavigationType = mCancelContentJSNavigationType;
+    cancelContentJSNavigationIndex = mCancelContentJSNavigationIndex;
+    cancelContentJSNavigationURI = std::move(mCancelContentJSNavigationURI);
+    cancelContentJSEpoch = mCancelContentJSEpoch;
+
+    mCancelContentJS = false;
+  }
+
+  if (cancelContentJS) {
+    js::AutoAssertNoContentJS nojs(mContext);
+
+    RefPtr<BrowserChild> browserChild =
+        BrowserChild::FindBrowserChild(cancelContentJSTab);
+    RefPtr<BrowserChild> browserChildFromWin = BrowserChild::GetFrom(win);
+    if (!browserChild || !browserChildFromWin) {
+      return true;
+    }
+
+    TabId tabIdFromWin = browserChildFromWin->GetTabId();
+    if (tabIdFromWin != cancelContentJSTab) {
+      // The currently-executing content JS doesn't belong to the tab that
+      // requested cancellation of JS. Just return and let the JS continue.
+      return true;
+    }
+
+    nsresult rv;
+    nsCOMPtr<nsIURI> uri;
+
+    if (cancelContentJSNavigationURI) {
+      rv = NS_NewURI(getter_AddRefs(uri), cancelContentJSNavigationURI.value());
+      if (NS_FAILED(rv)) {
+        return true;
+      }
+    }
+
+    bool canCancel;
+    rv = browserChild->CanCancelContentJS(cancelContentJSNavigationType,
+                                          cancelContentJSNavigationIndex, uri,
+                                          cancelContentJSEpoch, &canCancel);
+    if (NS_SUCCEEDED(rv) && canCancel) {
+      // Don't add this page to the BF cache, since we're cancelling its JS.
+      if (Document* doc = win->GetExtantDoc()) {
+        doc->DisallowBFCaching();
+      }
+
+      return false;
+    }
+  }
+
+  return true;
+}
+
+void HangMonitorChild::AnnotateHang(BackgroundHangAnnotations& aAnnotations) {
+  if (mPaintWhileInterruptingJSActive) {
+    aAnnotations.AddAnnotation(u"PaintWhileInterruptingJS"_ns, true);
+  }
+}
+
+void HangMonitorChild::Shutdown() {
+  ReleaseAssertIsOnMainThread();
+
+  BackgroundHangMonitor::UnregisterAnnotator(*this);
+
+  {
+    MonitorAutoLock lock(mMonitor);
+    while (!mShutdownDone) {
+      mMonitor.Wait();
+    }
+  }
+
+  MOZ_ASSERT(sInstance == this);
+  sInstance = nullptr;
+}
+
+void HangMonitorChild::ShutdownOnThread() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  MonitorAutoLock lock(mMonitor);
+  mShutdownDone = true;
+  mMonitor.Notify();
+}
+
+void HangMonitorChild::ActorDestroy(ActorDestroyReason aWhy) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  mIPCOpen = false;
+
+  // We use a task here to ensure that IPDL is finished with this
+  // HangMonitorChild before it gets deleted on the main thread.
+  Dispatch(NewNonOwningRunnableMethod("HangMonitorChild::ShutdownOnThread",
+                                      this,
+                                      &HangMonitorChild::ShutdownOnThread));
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvTerminateScript() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  MonitorAutoLock lock(mMonitor);
+  mTerminateScript = true;
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvRequestContentJSInterrupt() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  // In order to cancel JS execution on shutdown, we expect that
+  // ProcessChild::NotifiedImpendingShutdown has been called before.
+  if (mozilla::ipc::ProcessChild::ExpectingShutdown()) {
+    CrashReporter::AppendToCrashReportAnnotation(
+        CrashReporter::Annotation::IPCShutdownState,
+        "HangMonitorChild::RecvRequestContentJSInterrupt (expected)"_ns);
+  } else {
+    CrashReporter::AppendToCrashReportAnnotation(
+        CrashReporter::Annotation::IPCShutdownState,
+        "HangMonitorChild::RecvRequestContentJSInterrupt (unexpected)"_ns);
+  }
+  JS_RequestInterruptCallback(mContext);
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvBeginStartingDebugger() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  MonitorAutoLock lock(mMonitor);
+  mStartDebugger = true;
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvEndStartingDebugger() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  MonitorAutoLock lock(mMonitor);
+  mFinishedStartingDebugger = true;
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvPaintWhileInterruptingJS(
+    const TabId& aTabId) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  {
+    MonitorAutoLock lock(mMonitor);
+    MaybeStartPaintWhileInterruptingJS();
+    mPaintWhileInterruptingJS = Some(true);
+    mPaintWhileInterruptingJSTab = aTabId;
+  }
+
+  JS_RequestInterruptCallback(mContext);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvUnloadLayersWhileInterruptingJS(
+    const TabId& aTabId) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  {
+    MonitorAutoLock lock(mMonitor);
+    MaybeStartPaintWhileInterruptingJS();
+    mPaintWhileInterruptingJS = Some(false);
+    mPaintWhileInterruptingJSTab = aTabId;
+  }
+
+  JS_RequestInterruptCallback(mContext);
+
+  return IPC_OK();
+}
+
+void HangMonitorChild::MaybeStartPaintWhileInterruptingJS() {
+  mPaintWhileInterruptingJSActive = true;
+}
+
+void HangMonitorChild::ClearPaintWhileInterruptingJS() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  MOZ_RELEASE_ASSERT(XRE_IsContentProcess());
+  mPaintWhileInterruptingJSActive = false;
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvCancelContentJSExecutionIfRunning(
+    const TabId& aTabId, const nsIRemoteTab::NavigationType& aNavigationType,
+    const int32_t& aNavigationIndex,
+    const mozilla::Maybe<nsCString>& aNavigationURI, const int32_t& aEpoch) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  {
+    MonitorAutoLock lock(mMonitor);
+    mCancelContentJS = true;
+    mCancelContentJSTab = aTabId;
+    mCancelContentJSNavigationType = aNavigationType;
+    mCancelContentJSNavigationIndex = aNavigationIndex;
+    mCancelContentJSNavigationURI = aNavigationURI;
+    mCancelContentJSEpoch = aEpoch;
+  }
+
+  JS_RequestInterruptCallback(mContext);
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorChild::RecvSetMainThreadQoSPriority(
+    const nsIThread::QoSPriority& aQoSPriority) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+#ifdef XP_MACOSX
+  // If the new priority is the background (low) priority, we can tell the OS to
+  // put the main thread on low-power cores. Alternately, if we are changing
+  // from the background to a higher priority, we change the main thread back to
+  // the |user-interactive| state, defined in MacOS's QoS documentation as
+  // reserved for main threads.
+  qos_class_t qosClass = aQoSPriority == nsIThread::QOS_PRIORITY_LOW
+                             ? QOS_CLASS_BACKGROUND
+                             : QOS_CLASS_USER_INTERACTIVE;
+
+  // We can't directly set the main thread's QoS class from off-main-thread.
+  // However, we can start a QoS class override to raise the QoS, then dispatch
+  // a runnable to set the QoS class and clear the override once complete.
+  pthread_override_t qosOverride =
+      pthread_override_qos_class_start_np(mMainPThread, qosClass, 0);
+  if (NS_FAILED(NS_DispatchToMainThread(NS_NewRunnableFunction(
+          "HangMonitorChild::RecvSetMainThreadQoSPriority",
+          [qosClass, qosOverride] {
+            pthread_set_qos_class_self_np(qosClass, 0);
+            if (qosOverride) {
+              pthread_override_qos_class_end_np(qosOverride);
+            }
+          })))) {
+    // If we fail to dispatch, go ahead and end the override anyway.
+    pthread_override_qos_class_end_np(qosOverride);
+  }
+#endif
+
+  return IPC_OK();
+}
+
+void HangMonitorChild::Bind(Endpoint<PProcessHangMonitorChild>&& aEndpoint) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  DebugOnly<bool> ok = aEndpoint.Bind(this);
+  MOZ_ASSERT(ok);
+}
+
+void HangMonitorChild::NotifySlowScriptAsync(TabId aTabId,
+                                             const nsCString& aFileName,
+                                             const nsString& aAddonId,
+                                             const double aDuration) {
+  if (mIPCOpen) {
+    Unused << SendHangEvidence(
+        SlowScriptData(aTabId, aFileName, aAddonId, aDuration));
+  }
+}
+
+HangMonitorChild::SlowScriptAction HangMonitorChild::NotifySlowScript(
+    nsIBrowserChild* aBrowserChild, const char* aFileName,
+    const nsString& aAddonId, const double aDuration) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  mSentReport = true;
+
+  {
+    MonitorAutoLock lock(mMonitor);
+
+    if (mTerminateScript) {
+      mTerminateScript = false;
+      return SlowScriptAction::Terminate;
+    }
+
+    if (mStartDebugger) {
+      mStartDebugger = false;
+      return SlowScriptAction::StartDebugger;
+    }
+  }
+
+  TabId id;
+  if (aBrowserChild) {
+    RefPtr<BrowserChild> browserChild =
+        static_cast<BrowserChild*>(aBrowserChild);
+    id = browserChild->GetTabId();
+  }
+  nsAutoCString filename(aFileName);
+
+  Dispatch(NewNonOwningRunnableMethod<TabId, nsCString, nsString, double>(
+      "HangMonitorChild::NotifySlowScriptAsync", this,
+      &HangMonitorChild::NotifySlowScriptAsync, id, filename, aAddonId,
+      aDuration));
+  return SlowScriptAction::Continue;
+}
+
+bool HangMonitorChild::IsDebuggerStartupComplete() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  MonitorAutoLock lock(mMonitor);
+
+  if (mFinishedStartingDebugger) {
+    mFinishedStartingDebugger = false;
+    return true;
+  }
+
+  return false;
+}
+
+void HangMonitorChild::ClearHang() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (mSentReport) {
+    // bounce to background thread
+    Dispatch(NewNonOwningRunnableMethod("HangMonitorChild::ClearHangAsync",
+                                        this,
+                                        &HangMonitorChild::ClearHangAsync));
+
+    MonitorAutoLock lock(mMonitor);
+    mSentReport = false;
+    mTerminateScript = false;
+    mStartDebugger = false;
+    mFinishedStartingDebugger = false;
+  }
+}
+
+void HangMonitorChild::ClearHangAsync() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  // bounce back to parent on background thread
+  if (mIPCOpen) {
+    Unused << SendClearHang();
+  }
+}
+
+/* HangMonitorParent implementation */
+
+HangMonitorParent::HangMonitorParent(ProcessHangMonitor* aMonitor)
+    : mHangMonitor(aMonitor),
+      mIPCOpen(true),
+      mMonitor("HangMonitorParent lock"),
+      mShutdownDone(false),
+      mMainThreadTaskFactory(this) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+}
+
+void HangMonitorParent::Shutdown() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  MonitorAutoLock lock(mMonitor);
+
+  if (mProcess) {
+    mProcess->Clear();
+    mProcess = nullptr;
+  }
+
+  nsresult rv = Dispatch(
+      NewNonOwningRunnableMethod("HangMonitorParent::ShutdownOnThread", this,
+                                 &HangMonitorParent::ShutdownOnThread));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  while (!mShutdownDone) {
+    mMonitor.Wait();
+  }
+}
+
+void HangMonitorParent::ShutdownOnThread() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  // mIPCOpen is only written from this thread, so need need to take the lock
+  // here. We'd be shooting ourselves in the foot, because ActorDestroy takes
+  // it.
+  if (mIPCOpen) {
+    Close();
+  }
+
+  MonitorAutoLock lock(mMonitor);
+  mShutdownDone = true;
+  mMonitor.Notify();
+}
+
+void HangMonitorParent::PaintWhileInterruptingJS(dom::BrowserParent* aTab) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  if (StaticPrefs::browser_tabs_remote_force_paint()) {
+    TabId id = aTab->GetTabId();
+    Dispatch(NewNonOwningRunnableMethod<bool, TabId>(
+        "HangMonitorParent::PaintOrUnloadLayersWhileInterruptingJSOnThread ",
+        this,
+        &HangMonitorParent::PaintOrUnloadLayersWhileInterruptingJSOnThread,
+        true, id));
+  }
+}
+
+void HangMonitorParent::UnloadLayersWhileInterruptingJS(
+    dom::BrowserParent* aTab) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  TabId id = aTab->GetTabId();
+  Dispatch(NewNonOwningRunnableMethod<bool, TabId>(
+      "HangMonitorParent::PaintOrUnloadLayersWhileInterruptingJSOnThread ",
+      this, &HangMonitorParent::PaintOrUnloadLayersWhileInterruptingJSOnThread,
+      false, id));
+}
+
+void HangMonitorParent::PaintOrUnloadLayersWhileInterruptingJSOnThread(
+    const bool aPaint, TabId aTabId) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  if (mIPCOpen) {
+    if (aPaint) {
+      Unused << SendPaintWhileInterruptingJS(aTabId);
+    } else {
+      Unused << SendUnloadLayersWhileInterruptingJS(aTabId);
+    }
+  }
+}
+
+void HangMonitorParent::CancelContentJSExecutionIfRunning(
+    dom::BrowserParent* aBrowserParent,
+    nsIRemoteTab::NavigationType aNavigationType,
+    const dom::CancelContentJSOptions& aCancelContentJSOptions) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  if (!aBrowserParent->CanCancelContentJS(aNavigationType,
+                                          aCancelContentJSOptions.mIndex,
+                                          aCancelContentJSOptions.mUri)) {
+    return;
+  }
+
+  TabId id = aBrowserParent->GetTabId();
+  Dispatch(NewNonOwningRunnableMethod<TabId, nsIRemoteTab::NavigationType,
+                                      int32_t, nsIURI*, int32_t>(
+      "HangMonitorParent::CancelContentJSExecutionIfRunningOnThread", this,
+      &HangMonitorParent::CancelContentJSExecutionIfRunningOnThread, id,
+      aNavigationType, aCancelContentJSOptions.mIndex,
+      aCancelContentJSOptions.mUri, aCancelContentJSOptions.mEpoch));
+}
+
+void HangMonitorParent::CancelContentJSExecutionIfRunningOnThread(
+    TabId aTabId, nsIRemoteTab::NavigationType aNavigationType,
+    int32_t aNavigationIndex, nsIURI* aNavigationURI, int32_t aEpoch) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  mozilla::Maybe<nsCString> spec;
+  if (aNavigationURI) {
+    nsAutoCString tmp;
+    nsresult rv = aNavigationURI->GetSpec(tmp);
+    if (NS_SUCCEEDED(rv)) {
+      spec.emplace(tmp);
+    }
+  }
+
+  if (mIPCOpen) {
+    Unused << SendCancelContentJSExecutionIfRunning(
+        aTabId, aNavigationType, aNavigationIndex, spec, aEpoch);
+  }
+}
+
+void HangMonitorParent::SetMainThreadQoSPriority(
+    nsIThread::QoSPriority aQoSPriority) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+#ifdef XP_MACOSX  // Should not be using outside of MacOS.
+
+  Dispatch(NewNonOwningRunnableMethod<nsIThread::QoSPriority>(
+      "HangMonitorParent::SetMainThreadQoSPriorityOnThread", this,
+      &HangMonitorParent::SetMainThreadQoSPriorityOnThread, aQoSPriority));
+#endif
+}
+
+#ifdef XP_MACOSX
+void HangMonitorParent::SetMainThreadQoSPriorityOnThread(
+    nsIThread::QoSPriority aQoSPriority) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+  if (mIPCOpen) {
+    Unused << SendSetMainThreadQoSPriority(aQoSPriority);
+  }
+}
+#endif
+
+void HangMonitorParent::ActorDestroy(ActorDestroyReason aWhy) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+  mIPCOpen = false;
+}
+
+void HangMonitorParent::Bind(Endpoint<PProcessHangMonitorParent>&& aEndpoint) {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  DebugOnly<bool> ok = aEndpoint.Bind(this);
+  MOZ_ASSERT(ok);
+}
+
+void HangMonitorParent::SendHangNotification(
+    const SlowScriptData& aSlowScriptData, const nsString& aBrowserDumpId) {
+  // chrome process, main thread
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  nsString dumpId;
+
+  // We already have a full minidump; go ahead and use it.
+  dumpId = aBrowserDumpId;
+
+  mProcess->SetSlowScriptData(aSlowScriptData, dumpId);
+
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  observerService->NotifyObservers(mProcess, "process-hang-report", nullptr);
+}
+
+void HangMonitorParent::ClearHangNotification() {
+  // chrome process, main thread
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  nsCOMPtr<nsIObserverService> observerService =
+      mozilla::services::GetObserverService();
+  observerService->NotifyObservers(mProcess, "clear-hang-report", nullptr);
+
+  mProcess->ClearHang();
+}
+
+mozilla::ipc::IPCResult HangMonitorParent::RecvHangEvidence(
+    const SlowScriptData& aSlowScriptData) {
+  // chrome process, background thread
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  if (!StaticPrefs::dom_ipc_reportProcessHangs()) {
+    return IPC_OK();
+  }
+
+#ifdef XP_WIN
+  // Don't report hangs if we're debugging the process. You can comment this
+  // line out for testing purposes.
+  if (IsDebuggerPresent()) {
+    return IPC_OK();
+  }
+#endif
+
+  // Before we wake up the browser main thread we want to take a
+  // browser minidump.
+  nsAutoString crashId;
+
+  mHangMonitor->InitiateCPOWTimeout();
+
+  MonitorAutoLock lock(mMonitor);
+
+  NS_DispatchToMainThread(mMainThreadTaskFactory.NewRunnableMethod(
+      &HangMonitorParent::SendHangNotification, aSlowScriptData, crashId));
+
+  return IPC_OK();
+}
+
+mozilla::ipc::IPCResult HangMonitorParent::RecvClearHang() {
+  // chrome process, background thread
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  if (!StaticPrefs::dom_ipc_reportProcessHangs()) {
+    return IPC_OK();
+  }
+
+  mHangMonitor->InitiateCPOWTimeout();
+
+  MonitorAutoLock lock(mMonitor);
+
+  NS_DispatchToMainThread(mMainThreadTaskFactory.NewRunnableMethod(
+      &HangMonitorParent::ClearHangNotification));
+
+  return IPC_OK();
+}
+
+void HangMonitorParent::TerminateScript() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  if (mIPCOpen) {
+    Unused << SendTerminateScript();
+  }
+}
+
+void HangMonitorParent::BeginStartingDebugger() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  if (mIPCOpen) {
+    Unused << SendBeginStartingDebugger();
+  }
+}
+
+void HangMonitorParent::EndStartingDebugger() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+
+  if (mIPCOpen) {
+    Unused << SendEndStartingDebugger();
+  }
+}
+
+/* HangMonitoredProcess implementation */
+
+NS_IMPL_ISUPPORTS(HangMonitoredProcess, nsIHangReport)
+
+NS_IMETHODIMP
+HangMonitoredProcess::GetHangDuration(double* aHangDuration) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  *aHangDuration = mSlowScriptData.duration();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::GetScriptBrowser(Element** aBrowser) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  TabId tabId = mSlowScriptData.tabId();
+  if (!mContentParent) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+
+  nsTArray<PBrowserParent*> tabs;
+  mContentParent->ManagedPBrowserParent(tabs);
+  for (size_t i = 0; i < tabs.Length(); i++) {
+    BrowserParent* tp = BrowserParent::GetFrom(tabs[i]);
+    if (tp->GetTabId() == tabId) {
+      RefPtr<Element> node = tp->GetOwnerElement();
+      node.forget(aBrowser);
+      return NS_OK;
+    }
+  }
+
+  *aBrowser = nullptr;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::GetScriptFileName(nsACString& aFileName) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  aFileName = mSlowScriptData.filename();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::GetAddonId(nsAString& aAddonId) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  aAddonId = mSlowScriptData.addonId();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::TerminateScript() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  if (!mActor) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  ProcessHangMonitor::Get()->Dispatch(
+      NewNonOwningRunnableMethod("HangMonitorParent::TerminateScript", mActor,
+                                 &HangMonitorParent::TerminateScript));
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::BeginStartingDebugger() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  if (!mActor) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  ProcessHangMonitor::Get()->Dispatch(NewNonOwningRunnableMethod(
+      "HangMonitorParent::BeginStartingDebugger", mActor,
+      &HangMonitorParent::BeginStartingDebugger));
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::EndStartingDebugger() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  if (!mActor) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  ProcessHangMonitor::Get()->Dispatch(NewNonOwningRunnableMethod(
+      "HangMonitorParent::EndStartingDebugger", mActor,
+      &HangMonitorParent::EndStartingDebugger));
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::IsReportForBrowserOrChildren(nsFrameLoader* aFrameLoader,
+                                                   bool* aResult) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  MOZ_RELEASE_ASSERT(XRE_IsParentProcess());
+
+  if (!mActor) {
+    *aResult = false;
+    return NS_OK;
+  }
+
+  NS_ENSURE_STATE(aFrameLoader);
+
+  AutoTArray<RefPtr<BrowsingContext>, 10> bcs;
+  bcs.AppendElement(aFrameLoader->GetExtantBrowsingContext());
+  while (!bcs.IsEmpty()) {
+    RefPtr<BrowsingContext> bc = bcs[bcs.Length() - 1];
+    bcs.RemoveLastElement();
+    if (!bc) {
+      continue;
+    }
+    if (mContentParent == bc->Canonical()->GetContentParent()) {
+      *aResult = true;
+      return NS_OK;
+    }
+    bc->GetChildren(bcs);
+  }
+
+  *aResult = false;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+HangMonitoredProcess::UserCanceled() { return NS_OK; }
+
+NS_IMETHODIMP
+HangMonitoredProcess::GetChildID(uint64_t* aChildID) {
+  if (!mContentParent) {
+    return NS_ERROR_NOT_AVAILABLE;
+  }
+  *aChildID = mContentParent->ChildID();
+  return NS_OK;
+}
+
+static bool InterruptCallback(JSContext* cx) {
+  AssertIsOnMainThread();
+  if (HangMonitorChild* child = HangMonitorChild::Get()) {
+    return child->InterruptCallback();
+  }
+
+  return true;
+}
+
+ProcessHangMonitor* ProcessHangMonitor::sInstance;
+
+ProcessHangMonitor::ProcessHangMonitor() : mCPOWTimeout(false) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  if (XRE_IsContentProcess()) {
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    obs->AddObserver(this, "xpcom-shutdown", false);
+  }
+
+  if (NS_FAILED(NS_NewNamedThread("ProcessHangMon", getter_AddRefs(mThread)))) {
+    mThread = nullptr;
+  }
+#ifdef XP_MACOSX
+  // On MacOS, ensure the priority is high enough to handle dispatches at
+  // high cpu load. USER_INITIATED class threads are prioritized just below
+  // the main thread.
+  mThread->Dispatch(NS_NewRunnableFunction(
+      "ProcessHangMonitor::SetPriority",
+      [] { pthread_set_qos_class_self_np(QOS_CLASS_USER_INITIATED, 0); }));
+#endif
+}
+
+ProcessHangMonitor::~ProcessHangMonitor() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  MOZ_ASSERT(sInstance == this);
+  sInstance = nullptr;
+
+  mThread->Shutdown();
+  mThread = nullptr;
+}
+
+ProcessHangMonitor* ProcessHangMonitor::GetOrCreate() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  if (!sInstance) {
+    sInstance = new ProcessHangMonitor();
+  }
+  return sInstance;
+}
+
+NS_IMPL_ISUPPORTS(ProcessHangMonitor, nsIObserver)
+
+NS_IMETHODIMP
+ProcessHangMonitor::Observe(nsISupports* aSubject, const char* aTopic,
+                            const char16_t* aData) {
+  ReleaseAssertIsOnMainThread();
+  if (!strcmp(aTopic, "xpcom-shutdown")) {
+    if (RefPtr<HangMonitorChild> child = HangMonitorChild::Get()) {
+      child->Shutdown();
+    }
+
+    nsCOMPtr<nsIObserverService> obs = mozilla::services::GetObserverService();
+    obs->RemoveObserver(this, "xpcom-shutdown");
+  }
+  return NS_OK;
+}
+
+ProcessHangMonitor::SlowScriptAction ProcessHangMonitor::NotifySlowScript(
+    nsIBrowserChild* aBrowserChild, const char* aFileName,
+    const nsString& aAddonId, const double aDuration) {
+  ReleaseAssertIsOnMainThread();
+  return HangMonitorChild::Get()->NotifySlowScript(aBrowserChild, aFileName,
+                                                   aAddonId, aDuration);
+}
+
+bool ProcessHangMonitor::IsDebuggerStartupComplete() {
+  ReleaseAssertIsOnMainThread();
+  return HangMonitorChild::Get()->IsDebuggerStartupComplete();
+}
+
+bool ProcessHangMonitor::ShouldTimeOutCPOWs() {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  if (mCPOWTimeout) {
+    mCPOWTimeout = false;
+    return true;
+  }
+  return false;
+}
+
+void ProcessHangMonitor::InitiateCPOWTimeout() {
+  MOZ_RELEASE_ASSERT(IsOnThread());
+  mCPOWTimeout = true;
+}
+
+static already_AddRefed<PProcessHangMonitorParent> CreateHangMonitorParent(
+    ContentParent* aContentParent,
+    Endpoint<PProcessHangMonitorParent>&& aEndpoint) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  ProcessHangMonitor* monitor = ProcessHangMonitor::GetOrCreate();
+  RefPtr<HangMonitorParent> parent = new HangMonitorParent(monitor);
+
+  auto* process = new HangMonitoredProcess(parent, aContentParent);
+  parent->SetProcess(process);
+
+  monitor->Dispatch(
+      NewNonOwningRunnableMethod<Endpoint<PProcessHangMonitorParent>&&>(
+          "HangMonitorParent::Bind", parent, &HangMonitorParent::Bind,
+          std::move(aEndpoint)));
+
+  return parent.forget();
+}
+
+void mozilla::CreateHangMonitorChild(
+    Endpoint<PProcessHangMonitorChild>&& aEndpoint) {
+  ReleaseAssertIsOnMainThread();
+
+  JSContext* cx = danger::GetJSContext();
+  JS_AddInterruptCallback(cx, InterruptCallback);
+
+  ProcessHangMonitor* monitor = ProcessHangMonitor::GetOrCreate();
+  HangMonitorChild::CreateAndBind(monitor, std::move(aEndpoint));
+}
+
+nsresult ProcessHangMonitor::Dispatch(already_AddRefed<nsIRunnable> aRunnable) {
+  return mThread->Dispatch(std::move(aRunnable),
+                           nsIEventTarget::NS_DISPATCH_NORMAL);
+}
+
+bool ProcessHangMonitor::IsOnThread() {
+  bool on;
+  return NS_SUCCEEDED(mThread->IsOnCurrentThread(&on)) && on;
+}
+
+/* static */
+already_AddRefed<PProcessHangMonitorParent> ProcessHangMonitor::AddProcess(
+    ContentParent* aContentParent) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+
+  if (!StaticPrefs::dom_ipc_processHangMonitor_AtStartup()) {
+    return nullptr;
+  }
+
+  Endpoint<PProcessHangMonitorParent> parent;
+  Endpoint<PProcessHangMonitorChild> child;
+  nsresult rv;
+  rv = PProcessHangMonitor::CreateEndpoints(&parent, &child);
+  if (NS_FAILED(rv)) {
+    MOZ_ASSERT(false, "PProcessHangMonitor::CreateEndpoints failed");
+    return nullptr;
+  }
+
+  if (!aContentParent->SendInitProcessHangMonitor(std::move(child))) {
+    MOZ_ASSERT(false);
+    return nullptr;
+  }
+
+  return CreateHangMonitorParent(aContentParent, std::move(parent));
+}
+
+/* static */
+void ProcessHangMonitor::RemoveProcess(PProcessHangMonitorParent* aParent) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  auto parent = static_cast<HangMonitorParent*>(aParent);
+  parent->Shutdown();
+}
+
+/* static */
+void ProcessHangMonitor::ClearHang() {
+  AssertIsOnMainThread();
+  if (HangMonitorChild* child = HangMonitorChild::Get()) {
+    child->ClearHang();
+  }
+}
+
+/* static */
+void ProcessHangMonitor::PaintWhileInterruptingJS(
+    PProcessHangMonitorParent* aParent, dom::BrowserParent* aTab) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  auto* parent = static_cast<HangMonitorParent*>(aParent);
+  parent->PaintWhileInterruptingJS(aTab);
+}
+
+/* static */
+void ProcessHangMonitor::UnloadLayersWhileInterruptingJS(
+    PProcessHangMonitorParent* aParent, dom::BrowserParent* aTab) {
+  MOZ_RELEASE_ASSERT(NS_IsMainThread());
+  auto* parent = static_cast<HangMonitorParent*>(aParent);
+  parent->UnloadLayersWhileInterruptingJS(aTab);
+}
+
+/* static */
+void ProcessHangMonitor::ClearPaintWhileInterruptingJS() {
+  ReleaseAssertIsOnMainThread();
+  MOZ_RELEASE_ASSERT(XRE_IsContentProcess());
+
+  if (HangMonitorChild* child = HangMonitorChild::Get()) {
+    child->ClearPaintWhileInterruptingJS();
+  }
+}
+
+/* static */
+void ProcessHangMonitor::MaybeStartPaintWhileInterruptingJS() {
+  ReleaseAssertIsOnMainThread();
+  MOZ_RELEASE_ASSERT(XRE_IsContentProcess());
+
+  if (HangMonitorChild* child = HangMonitorChild::Get()) {
+    child->MaybeStartPaintWhileInterruptingJS();
+  }
+}
+
+/* static */
+void ProcessHangMonitor::CancelContentJSExecutionIfRunning(
+    PProcessHangMonitorParent* aParent, dom::BrowserParent* aBrowserParent,
+    nsIRemoteTab::NavigationType aNavigationType,
+    const dom::CancelContentJSOptions& aCancelContentJSOptions) {
+  ReleaseAssertIsOnMainThread();
+  auto* parent = static_cast<HangMonitorParent*>(aParent);
+  parent->CancelContentJSExecutionIfRunning(aBrowserParent, aNavigationType,
+                                            aCancelContentJSOptions);
+}
+
+/* static */
+void ProcessHangMonitor::SetMainThreadQoSPriority(
+    PProcessHangMonitorParent* aParent, nsIThread::QoSPriority aQoSPriority) {
+  ReleaseAssertIsOnMainThread();
+  auto* parent = static_cast<HangMonitorParent*>(aParent);
+  parent->SetMainThreadQoSPriority(aQoSPriority);
+}