1 files changed, 407 insertions, 0 deletions
diff --git a/xpcom/base/AvailableMemoryWatcherWin.cpp b/xpcom/base/AvailableMemoryWatcherWin.cpp
new file mode 100644
index 0000000000..42e590e93a
--- /dev/null
+++ b/xpcom/base/AvailableMemoryWatcherWin.cpp
@@ -0,0 +1,407 @@
+/* -*- 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 "AvailableMemoryWatcher.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "nsAppRunner.h"
+#include "nsExceptionHandler.h"
+#include "nsICrashReporter.h"
+#include "nsIObserver.h"
+#include "nsISupports.h"
+#include "nsITimer.h"
+#include "nsMemoryPressure.h"
+#include "nsServiceManagerUtils.h"
+#include "nsWindowsHelpers.h"
+
+#include <memoryapi.h>
+
+extern mozilla::Atomic<uint32_t, mozilla::MemoryOrdering::Relaxed>
+    sNumLowPhysicalMemEvents;
+
+namespace mozilla {
+
+// This class is used to monitor low memory events delivered by Windows via
+// memory resource notification objects. When we enter a low memory scenario
+// the LowMemoryCallback() is invoked by Windows. This initial call triggers
+// an nsITimer that polls to see when the low memory condition has been lifted.
+// When it has, we'll stop polling and start waiting for the next
+// LowMemoryCallback(). Meanwhile, the polling may be stopped and restarted by
+// user-interaction events from the observer service.
+class nsAvailableMemoryWatcher final : public nsITimerCallback,
+                                       public nsINamed,
+                                       public nsAvailableMemoryWatcherBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSITIMERCALLBACK
+  NS_DECL_NSINAMED
+
+  nsAvailableMemoryWatcher();
+  nsresult Init() override;
+
+ private:
+  static VOID CALLBACK LowMemoryCallback(PVOID aContext, BOOLEAN aIsTimer);
+  static void RecordLowMemoryEvent();
+  static bool IsCommitSpaceLow();
+
+  ~nsAvailableMemoryWatcher();
+  bool RegisterMemoryResourceHandler(const MutexAutoLock& aLock)
+      MOZ_REQUIRES(mMutex);
+  void UnregisterMemoryResourceHandler(const MutexAutoLock&)
+      MOZ_REQUIRES(mMutex);
+  void MaybeSaveMemoryReport(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void Shutdown(const MutexAutoLock& aLock) MOZ_REQUIRES(mMutex);
+  bool ListenForLowMemory(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void OnLowMemory(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void OnHighMemory(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void StartPollingIfUserInteracting(const MutexAutoLock& aLock)
+      MOZ_REQUIRES(mMutex);
+  void StopPolling(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void StopPollingIfUserIdle(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+  void OnUserInteracting(const MutexAutoLock&) MOZ_REQUIRES(mMutex);
+
+  // The publicly available methods (::Observe() and ::Notify()) are called on
+  // the main thread while the ::LowMemoryCallback() method is called by an
+  // external thread. All functions called from those must acquire a lock on
+  // this mutex before accessing the object's fields to prevent races.
+  Mutex mMutex;
+  nsCOMPtr<nsITimer> mTimer MOZ_GUARDED_BY(mMutex);
+  nsAutoHandle mLowMemoryHandle MOZ_GUARDED_BY(mMutex);
+  HANDLE mWaitHandle MOZ_GUARDED_BY(mMutex);
+  bool mPolling MOZ_GUARDED_BY(mMutex);
+
+  // Indicates whether to start a timer when user interaction is notified.
+  // This flag is needed because the low-memory callback may be triggered when
+  // the user is inactive and we want to delay-start the timer.
+  bool mNeedToRestartTimerOnUserInteracting MOZ_GUARDED_BY(mMutex);
+  // Indicate that the available commit space is low.  The timer handler needs
+  // this flag because it is triggered by the low physical memory regardless
+  // of the available commit space.
+  bool mUnderMemoryPressure MOZ_GUARDED_BY(mMutex);
+
+  bool mSavedReport MOZ_GUARDED_BY(mMutex);
+  bool mIsShutdown MOZ_GUARDED_BY(mMutex);
+
+  // Members below this line are used only in the main thread.
+  // No lock is needed.
+
+  // Don't fire a low-memory notification more often than this interval.
+  uint32_t mPollingInterval;
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(nsAvailableMemoryWatcher,
+                            nsAvailableMemoryWatcherBase, nsIObserver,
+                            nsITimerCallback, nsINamed)
+
+nsAvailableMemoryWatcher::nsAvailableMemoryWatcher()
+    : mMutex("low memory callback mutex"),
+      mWaitHandle(nullptr),
+      mPolling(false),
+      mNeedToRestartTimerOnUserInteracting(false),
+      mUnderMemoryPressure(false),
+      mSavedReport(false),
+      mIsShutdown(false),
+      mPollingInterval(0) {}
+
+nsresult nsAvailableMemoryWatcher::Init() {
+  nsresult rv = nsAvailableMemoryWatcherBase::Init();
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  MutexAutoLock lock(mMutex);
+  mTimer = NS_NewTimer();
+  if (!mTimer) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  // Use a very short interval for GTest to verify the timer's behavior.
+  mPollingInterval = gIsGtest ? 10 : 10000;
+
+  if (!RegisterMemoryResourceHandler(lock)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+nsAvailableMemoryWatcher::~nsAvailableMemoryWatcher() {
+  // These handles should have been released during the shutdown phase.
+  MOZ_ASSERT(!mLowMemoryHandle);
+  MOZ_ASSERT(!mWaitHandle);
+}
+
+// static
+VOID CALLBACK nsAvailableMemoryWatcher::LowMemoryCallback(PVOID aContext,
+                                                          BOOLEAN aIsTimer) {
+  if (aIsTimer) {
+    return;
+  }
+
+  // The |watcher| was addref'ed when we registered the wait handle in
+  // ListenForLowMemory().  It is decremented when exiting the function,
+  // so please make sure we unregister the wait handle after this line.
+  RefPtr<nsAvailableMemoryWatcher> watcher =
+      already_AddRefed<nsAvailableMemoryWatcher>(
+          static_cast<nsAvailableMemoryWatcher*>(aContext));
+
+  MutexAutoLock lock(watcher->mMutex);
+  if (watcher->mIsShutdown) {
+    // mWaitHandle should have been unregistered during shutdown
+    MOZ_ASSERT(!watcher->mWaitHandle);
+    return;
+  }
+
+  ::UnregisterWait(watcher->mWaitHandle);
+  watcher->mWaitHandle = nullptr;
+
+  // On Windows, memory allocations fails when the available commit space is
+  // not sufficient.  It's possible that this callback function is invoked
+  // but there is still commit space enough for the application to continue
+  // to run.  In such a case, there is no strong need to trigger the memory
+  // pressure event.  So we trigger the event only when the available commit
+  // space is low.
+  if (IsCommitSpaceLow()) {
+    watcher->OnLowMemory(lock);
+  } else {
+    // Since we have unregistered the callback, we need to start a timer to
+    // continue watching memory.
+    watcher->StartPollingIfUserInteracting(lock);
+  }
+}
+
+// static
+void nsAvailableMemoryWatcher::RecordLowMemoryEvent() {
+  sNumLowPhysicalMemEvents++;
+  CrashReporter::AnnotateCrashReport(
+      CrashReporter::Annotation::LowPhysicalMemoryEvents,
+      sNumLowPhysicalMemEvents);
+}
+
+bool nsAvailableMemoryWatcher::RegisterMemoryResourceHandler(
+    const MutexAutoLock& aLock) {
+  mLowMemoryHandle.own(
+      ::CreateMemoryResourceNotification(LowMemoryResourceNotification));
+
+  if (!mLowMemoryHandle) {
+    return false;
+  }
+
+  return ListenForLowMemory(aLock);
+}
+
+void nsAvailableMemoryWatcher::UnregisterMemoryResourceHandler(
+    const MutexAutoLock&) {
+  if (mWaitHandle) {
+    bool res = ::UnregisterWait(mWaitHandle);
+    if (res || ::GetLastError() != ERROR_IO_PENDING) {
+      // We decrement the refcount only when we're sure the LowMemoryCallback()
+      // callback won't be invoked, otherwise the callback will do it
+      this->Release();
+    }
+    mWaitHandle = nullptr;
+  }
+
+  mLowMemoryHandle.reset();
+}
+
+void nsAvailableMemoryWatcher::Shutdown(const MutexAutoLock& aLock) {
+  mIsShutdown = true;
+  mNeedToRestartTimerOnUserInteracting = false;
+
+  if (mTimer) {
+    mTimer->Cancel();
+    mTimer = nullptr;
+  }
+
+  UnregisterMemoryResourceHandler(aLock);
+}
+
+bool nsAvailableMemoryWatcher::ListenForLowMemory(const MutexAutoLock&) {
+  if (mLowMemoryHandle && !mWaitHandle) {
+    // We're giving ownership of this object to the LowMemoryCallback(). We
+    // increment the count here so that the object is kept alive until the
+    // callback decrements it.
+    this->AddRef();
+    bool res = ::RegisterWaitForSingleObject(
+        &mWaitHandle, mLowMemoryHandle, LowMemoryCallback, this, INFINITE,
+        WT_EXECUTEDEFAULT | WT_EXECUTEONLYONCE);
+    if (!res) {
+      // We couldn't register the callback, decrement the count
+      this->Release();
+    }
+    // Once we register the wait handle, we no longer need to start
+    // the timer because we can continue watching memory via callback.
+    mNeedToRestartTimerOnUserInteracting = false;
+    return res;
+  }
+
+  return false;
+}
+
+void nsAvailableMemoryWatcher::MaybeSaveMemoryReport(const MutexAutoLock&) {
+  if (mSavedReport) {
+    return;
+  }
+
+  if (nsCOMPtr<nsICrashReporter> cr =
+          do_GetService("@mozilla.org/toolkit/crash-reporter;1")) {
+    mSavedReport = NS_SUCCEEDED(cr->SaveMemoryReport());
+  }
+}
+
+void nsAvailableMemoryWatcher::OnLowMemory(const MutexAutoLock& aLock) {
+  mUnderMemoryPressure = true;
+  RecordLowMemoryEvent();
+
+  if (NS_IsMainThread()) {
+    MaybeSaveMemoryReport(aLock);
+    UpdateLowMemoryTimeStamp();
+    {
+      // Don't invoke UnloadTabAsync() with the lock to avoid deadlock
+      // because nsAvailableMemoryWatcher::Notify may be invoked while
+      // running the method.
+      MutexAutoUnlock unlock(mMutex);
+      mTabUnloader->UnloadTabAsync();
+    }
+  } else {
+    // SaveMemoryReport and mTabUnloader needs to be run in the main thread
+    // (See nsMemoryReporterManager::GetReportsForThisProcessExtended)
+    NS_DispatchToMainThread(NS_NewRunnableFunction(
+        "nsAvailableMemoryWatcher::OnLowMemory", [self = RefPtr{this}]() {
+          {
+            MutexAutoLock lock(self->mMutex);
+            self->MaybeSaveMemoryReport(lock);
+            self->UpdateLowMemoryTimeStamp();
+          }
+          self->mTabUnloader->UnloadTabAsync();
+        }));
+  }
+
+  StartPollingIfUserInteracting(aLock);
+}
+
+void nsAvailableMemoryWatcher::OnHighMemory(const MutexAutoLock& aLock) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (mUnderMemoryPressure) {
+    RecordTelemetryEventOnHighMemory();
+    NS_NotifyOfEventualMemoryPressure(MemoryPressureState::NoPressure);
+  }
+
+  mUnderMemoryPressure = false;
+  mSavedReport = false;  // Will save a new report if memory gets low again
+  StopPolling(aLock);
+  ListenForLowMemory(aLock);
+}
+
+// static
+bool nsAvailableMemoryWatcher::IsCommitSpaceLow() {
+  // Other options to get the available page file size:
+  //   - GetPerformanceInfo
+  //     Too slow, don't use it.
+  //   - PdhCollectQueryData and PdhGetRawCounterValue
+  //     Faster than GetPerformanceInfo, but slower than GlobalMemoryStatusEx.
+  //   - NtQuerySystemInformation(SystemMemoryUsageInformation)
+  //     Faster than GlobalMemoryStatusEx, but undocumented.
+  MEMORYSTATUSEX memStatus = {sizeof(memStatus)};
+  if (!::GlobalMemoryStatusEx(&memStatus)) {
+    return false;
+  }
+
+  constexpr size_t kBytesPerMB = 1024 * 1024;
+  return (memStatus.ullAvailPageFile / kBytesPerMB) <
+         StaticPrefs::browser_low_commit_space_threshold_mb();
+}
+
+void nsAvailableMemoryWatcher::StartPollingIfUserInteracting(
+    const MutexAutoLock&) {
+  // When the user is inactive, we mark the flag to delay-start
+  // the timer when the user becomes active later.
+  mNeedToRestartTimerOnUserInteracting = true;
+
+  if (mInteracting && !mPolling) {
+    if (NS_SUCCEEDED(mTimer->InitWithCallback(
+            this, mPollingInterval, nsITimer::TYPE_REPEATING_SLACK))) {
+      mPolling = true;
+    }
+  }
+}
+
+void nsAvailableMemoryWatcher::StopPolling(const MutexAutoLock&) {
+  mTimer->Cancel();
+  mPolling = false;
+}
+
+void nsAvailableMemoryWatcher::StopPollingIfUserIdle(
+    const MutexAutoLock& aLock) {
+  if (!mInteracting) {
+    StopPolling(aLock);
+  }
+}
+
+void nsAvailableMemoryWatcher::OnUserInteracting(const MutexAutoLock& aLock) {
+  if (mNeedToRestartTimerOnUserInteracting) {
+    StartPollingIfUserInteracting(aLock);
+  }
+}
+
+// Timer callback, polls the low memory resource notification to detect when
+// we've freed enough memory or if we have to send more memory pressure events.
+// Polling stops automatically when the user is not interacting with the UI.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Notify(nsITimer* aTimer) {
+  MutexAutoLock lock(mMutex);
+  StopPollingIfUserIdle(lock);
+
+  if (IsCommitSpaceLow()) {
+    OnLowMemory(lock);
+  } else {
+    OnHighMemory(lock);
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::GetName(nsACString& aName) {
+  aName.AssignLiteral("nsAvailableMemoryWatcher");
+  return NS_OK;
+}
+
+// Observer service callback, used to stop the polling timer when the user
+// stops interacting with Firefox and resuming it when they interact again.
+// Also used to shut down the service if the application is quitting.
+NS_IMETHODIMP
+nsAvailableMemoryWatcher::Observe(nsISupports* aSubject, const char* aTopic,
+                                  const char16_t* aData) {
+  nsresult rv = nsAvailableMemoryWatcherBase::Observe(aSubject, aTopic, aData);
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  MutexAutoLock lock(mMutex);
+
+  if (strcmp(aTopic, "xpcom-shutdown") == 0) {
+    Shutdown(lock);
+  } else if (strcmp(aTopic, "user-interaction-active") == 0) {
+    OnUserInteracting(lock);
+  }
+
+  return NS_OK;
+}
+
+already_AddRefed<nsAvailableMemoryWatcherBase> CreateAvailableMemoryWatcher() {
+  RefPtr watcher(new nsAvailableMemoryWatcher);
+  if (NS_FAILED(watcher->Init())) {
+    return do_AddRef(new nsAvailableMemoryWatcherBase);  // fallback
+  }
+  return watcher.forget();
+}
+
+}  // namespace mozilla