Use JavaObjectWeakGlobalRef in ContentViewCore.

Java ContentViewCore object may be garbage
collected without first destroying the native object. Because of this,
all C++->Java calls to ContentViewCore must be guarded with a null
check.

BUG=139386,138237


Review URL: https://chromiumcodereview.appspot.com/10827125

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@149570 0039d316-1c4b-4281-b951-d872f2087c98

2 files changed, 21 insertions, 7 deletions

diff --git a/base/android/jni_helper.cc b/base/android/jni_helper.cc
index 5e9f409..3ff3bfb 100644
--- a/base/android/jni_helper.cc
+++ b/base/android/jni_helper.cc
@@ -15,8 +15,14 @@ JavaObjectWeakGlobalRef::JavaObjectWeakGlobalRef(JNIEnv* env, jobject obj)
 }
 
 JavaObjectWeakGlobalRef::~JavaObjectWeakGlobalRef() {
-  DCHECK(obj_);
-  AttachCurrentThread()->DeleteWeakGlobalRef(obj_);
+  reset();
+}
+
+void JavaObjectWeakGlobalRef::reset() {
+  if (obj_) {
+    AttachCurrentThread()->DeleteWeakGlobalRef(obj_);
+    obj_ = NULL;
+  }
 }
 
 base::android::ScopedJavaLocalRef<jobject>
@@ -25,9 +31,12 @@ base::android::ScopedJavaLocalRef<jobject>
 }
 
 base::android::ScopedJavaLocalRef<jobject> GetRealObject(
-    JNIEnv* env, jobject obj) {
-  jobject real = env->NewLocalRef(obj);
-  if (!real)
-    DLOG(ERROR) << "The real object has been deleted!";
+    JNIEnv* env, jweak obj) {
+  jobject real = NULL;
+  if (obj) {
+    real = env->NewLocalRef(obj);
+    if (!real)
+      DLOG(ERROR) << "The real object has been deleted!";
+  }
   return base::android::ScopedJavaLocalRef<jobject>(env, real);
 }
diff --git a/base/android/jni_helper.h b/base/android/jni_helper.h
index 61359ef..bd3579f 100644
--- a/base/android/jni_helper.h
+++ b/base/android/jni_helper.h
@@ -10,6 +10,9 @@
 #include "base/android/scoped_java_ref.h"
 
 // Manages WeakGlobalRef lifecycle.
+// This class is not thread-safe w.r.t. get() and reset(). Multiple threads may
+// safely use get() concurrently, but if the user calls reset() (or of course,
+// calls the destructor) they'll need to provide their own synchronization.
 class JavaObjectWeakGlobalRef {
  public:
   JavaObjectWeakGlobalRef(JNIEnv* env, jobject obj);
@@ -17,6 +20,8 @@ class JavaObjectWeakGlobalRef {
 
   base::android::ScopedJavaLocalRef<jobject> get(JNIEnv* env) const;
 
+  void reset();
+
  private:
   jweak obj_;
 
@@ -26,6 +31,6 @@ class JavaObjectWeakGlobalRef {
 // Get the real object stored in the weak reference returned as a
 // ScopedJavaLocalRef.
 base::android::ScopedJavaLocalRef<jobject> GetRealObject(
-    JNIEnv* env, jobject obj);
+    JNIEnv* env, jweak obj);
 
 #endif  // BASE_ANDROID_JNI_HELPER_H_