1 files changed, 77 insertions, 0 deletions
diff --git a/gfx/layers/MemoryPressureObserver.cpp b/gfx/layers/MemoryPressureObserver.cpp
new file mode 100644
index 0000000000..16c9ea4b1e
--- /dev/null
+++ b/gfx/layers/MemoryPressureObserver.cpp
@@ -0,0 +1,77 @@
+/* -*- 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 "MemoryPressureObserver.h"
+
+#include "mozilla/Services.h"
+#include "nsCOMPtr.h"
+#include "nsDependentString.h"
+#include "nsIObserverService.h"
+#include "nsLiteralString.h"
+
+namespace mozilla {
+namespace layers {
+
+MemoryPressureObserver::MemoryPressureObserver(
+    MemoryPressureListener* aListener)
+    : mListener(aListener) {}
+
+MemoryPressureObserver::~MemoryPressureObserver() {
+  // If this assertion is hit we probably forgot to unregister the observer.
+  MOZ_ASSERT(!mListener);
+}
+
+already_AddRefed<MemoryPressureObserver> MemoryPressureObserver::Create(
+    MemoryPressureListener* aListener) {
+  nsCOMPtr<nsIObserverService> service = services::GetObserverService();
+
+  if (!service) {
+    return nullptr;
+  }
+
+  RefPtr<MemoryPressureObserver> observer =
+      new MemoryPressureObserver(aListener);
+
+  bool useWeakRef = false;
+  service->AddObserver(observer, "memory-pressure", useWeakRef);
+
+  return observer.forget();
+}
+
+void MemoryPressureObserver::Unregister() {
+  if (!mListener) {
+    return;
+  }
+
+  nsCOMPtr<nsIObserverService> service = services::GetObserverService();
+  if (service) {
+    service->RemoveObserver(this, "memory-pressure");
+  }
+
+  mListener = nullptr;
+}
+
+NS_IMETHODIMP
+MemoryPressureObserver::Observe(nsISupports* aSubject, const char* aTopic,
+                                const char16_t* aData) {
+  if (mListener && strcmp(aTopic, "memory-pressure") == 0) {
+    MemoryPressureReason reason = MemoryPressureReason::LOW_MEMORY;
+    auto reason_string = nsDependentString(aData);
+    if (StringBeginsWith(reason_string, u"low-memory-ongoing"_ns)) {
+      reason = MemoryPressureReason::LOW_MEMORY_ONGOING;
+    } else if (StringBeginsWith(reason_string, u"heap-minimize"_ns)) {
+      reason = MemoryPressureReason::HEAP_MINIMIZE;
+    }
+    mListener->OnMemoryPressure(reason);
+  }
+
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(MemoryPressureObserver, nsIObserver)
+
+}  // namespace layers
+}  // namespace mozilla