Decouple MediaSession messages from WebContents (full patch)

content/browser/media/session/media_session_android.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/media/session/media_session_android.h"
+
+#include <algorithm>
+#include "content/browser/media/session/media_session_impl.h"
+#include "content/browser/web_contents/web_contents_android.h"
+#include "content/browser/web_contents/web_contents_impl.h"
+#include "content/common/android/media_metadata_android.h"
+#include "content/public/browser/media_session.h"
+#include "jni/MediaSessionImpl_jni.h"
+
+namespace content {
+
+using base::android::JavaParamRef;
+
+struct MediaSessionAndroid::JavaObjectGetter {
+  static const JavaObjectWeakGlobalRef& GetJavaObject(
+      MediaSessionAndroid* session_android) {
+    return session_android->j_media_session_;
+  }
+};
+
+MediaSessionAndroid::MediaSessionAndroid(MediaSessionImpl* session)
+    : MediaSessionObserver(session) {
+  JNIEnv* env = base::android::AttachCurrentThread();
+  base::android::ScopedJavaLocalRef<jobject> j_media_session =
+      Java_MediaSessionImpl_create(env, reinterpret_cast<intptr_t>(this));
+  j_media_session_ = JavaObjectWeakGlobalRef(env, j_media_session);
+
+  WebContentsAndroid* contents_android = GetWebContentsAndroid();
+  if (contents_android)
+    contents_android->SetMediaSession(j_media_session);
+}
+
+MediaSessionAndroid::~MediaSessionAndroid() {
+  // MediaSessionDestroyed() should have already been called.
+  DCHECK(j_media_session_.is_empty());
+}
+
+// static
+bool MediaSessionAndroid::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
+}
+
+// static
+base::android::ScopedJavaLocalRef<jobject> GetMediaSessionFromWebContents(
+    JNIEnv* env,
+    const JavaParamRef<jclass>& clazz,
+    const JavaParamRef<jobject>& j_contents_android) {
+  WebContents* contents = WebContents::FromJavaWebContents(j_contents_android);
+  if (!contents)
+    return base::android::ScopedJavaLocalRef<jobject>();
+
+  MediaSessionImpl* session = MediaSessionImpl::Get(contents);
+  DCHECK(session);
+  return MediaSessionAndroid::JavaObjectGetter::GetJavaObject(
+             session->session_android())
+      .get(env);
+}
+
+void MediaSessionAndroid::MediaSessionDestroyed() {
+  if (j_media_session_.is_empty())
+    return;
+
+  JNIEnv* env = base::android::AttachCurrentThread();
+  // The Java object will tear down after this call.
+  Java_MediaSessionImpl_mediaSessionDestroyed(env, j_media_session_.get(env));
+  j_media_session_.reset();
+
+  WebContentsAndroid* contents_android = GetWebContentsAndroid();
+  if (contents_android)
+    contents_android->SetMediaSession(nullptr);
+}
+
+void MediaSessionAndroid::MediaSessionStateChanged(bool is_controllable,
+                                                   bool is_suspended) {
+  if (j_media_session_.is_empty())

[boliu, 2016/10/31 22:44:02]

in theory, this check is not safe, there is no guarantee gc is single threaded,
and it should be possible for gc to run after this check, in which case you'll
get a null pointer. (in practice, I'm not entirely sure if art actually does
that, but better be safe than sorry..)

you need to make it into a ScopedJavaLocalRef, then check for null on the local
ref

[Zhiqiang Zhang (Slow), 2016/10/31 23:30:29]

Yes, you mentioned this before and I lost it after several refactoring. They are
fixed now.

+    return;
+
+  JNIEnv* env = base::android::AttachCurrentThread();
+  Java_MediaSessionImpl_mediaSessionStateChanged(env, j_media_session_.get(env),
+                                                 is_controllable, is_suspended);
+}
+
+void MediaSessionAndroid::MediaSessionMetadataChanged(
+    const base::Optional<MediaMetadata>& metadata) {
+  if (j_media_session_.is_empty())
+    return;
+
+  JNIEnv* env = base::android::AttachCurrentThread();
+
+  // Avoid translating metadata through JNI if there is no Java observer.
+  if (!Java_MediaSessionImpl_hasObservers(env, j_media_session_.get(env)))
+    return;
+
+  base::android::ScopedJavaLocalRef<jobject> j_metadata;
+  if (metadata.has_value())
+    j_metadata = MediaMetadataAndroid::CreateJavaObject(env, metadata.value());
+  Java_MediaSessionImpl_mediaSessionMetadataChanged(
+      env, j_media_session_.get(env), j_metadata);
+}
+
+void MediaSessionAndroid::Resume(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_obj) {
+  DCHECK(media_session());
+  media_session()->Resume(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionAndroid::Suspend(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_obj) {
+  DCHECK(media_session());
+  media_session()->Suspend(MediaSession::SuspendType::UI);
+}
+
+void MediaSessionAndroid::Stop(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jobject>& j_obj) {
+  DCHECK(media_session());
+  media_session()->Stop(MediaSession::SuspendType::UI);
+}
+
+WebContentsAndroid* MediaSessionAndroid::GetWebContentsAndroid() {
+  MediaSessionImpl* session = static_cast<MediaSessionImpl*>(media_session());
+  if (!session)
+    return nullptr;
+  WebContentsImpl* contents =
+      static_cast<WebContentsImpl*>(session->web_contents());
+  if (!contents)
+    return nullptr;
+  return contents->GetWebContentsAndroid();
+}
+
+}  // namespace content