Bug 1657404 - Use WeakPtr for observer pattern in GamepadPlatformService r=handyman

Differential Revision: https://phabricator.services.mozilla.com/D93085

dom/gamepad/GamepadPlatformService.cpp

@@ -34,7 +34,7 @@ GamepadPlatformService::MonitoringState::~MonitoringState() {
 }
 
 void GamepadPlatformService::MonitoringState::AddObserver(
-    RefPtr<GamepadTestChannelParent> aParent) {
+    WeakPtr<GamepadTestChannelParent> aParent) {
   AssertIsOnBackgroundThread();
   MOZ_ASSERT(aParent);
   MOZ_ASSERT(!mObservers.Contains(aParent));
@@ -60,6 +60,9 @@ void GamepadPlatformService::MonitoringState::Set(bool aIsMonitoring) {
   if (mIsMonitoring != aIsMonitoring) {
     mIsMonitoring = aIsMonitoring;
     for (auto& observer : mObservers) {
+      // Since each GamepadTestChannelParent removes itself in its dtor, this
+      // should never be nullptr
+      MOZ_RELEASE_ASSERT(observer);
       observer->OnMonitoringStateChanged(aIsMonitoring);
     }
   }

dom/gamepad/GamepadPlatformService.h

@@ -12,6 +12,7 @@
 #include <map>
 #include "mozilla/Mutex.h"
 #include "mozilla/StaticPtr.h"
+#include "mozilla/WeakPtr.h"
 
 namespace mozilla {
 namespace dom {
@@ -39,7 +40,7 @@ class GamepadPlatformService final {
     MonitoringState() = default;
     ~MonitoringState();
 
-    void AddObserver(RefPtr<GamepadTestChannelParent> aParent);
+    void AddObserver(WeakPtr<GamepadTestChannelParent> aParent);
     void RemoveObserver(GamepadTestChannelParent* aParent);
 
     bool IsMonitoring() const;
@@ -53,7 +54,7 @@ class GamepadPlatformService final {
     void Set(bool aIsMonitoring);
 
     bool mIsMonitoring{false};
-    nsTArray<RefPtr<GamepadTestChannelParent>> mObservers;
+    nsTArray<WeakPtr<GamepadTestChannelParent>> mObservers;
 
     friend class GamepadPlatformService;
   };

dom/gamepad/ipc/GamepadTestChannelParent.h

@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/dom/PGamepadTestChannelParent.h"
+#include "mozilla/WeakPtr.h"
 
 #ifndef mozilla_dom_GamepadTestChannelParent_h_
 #  define mozilla_dom_GamepadTestChannelParent_h_
@@ -12,7 +13,8 @@
 namespace mozilla {
 namespace dom {
 
-class GamepadTestChannelParent final : public PGamepadTestChannelParent {
+class GamepadTestChannelParent final : public PGamepadTestChannelParent,
+                                       public SupportsWeakPtr {
  public:
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(GamepadTestChannelParent)