Add MemoryMonitorAndroid

content/browser/memory/memory_monitor_android.cc

-// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// 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/memory/memory_monitor_android.h"
 
 #include "base/android/context_utils.h"
 #include "base/android/jni_android.h"
 #include "base/memory/ptr_util.h"
 #include "jni/MemoryMonitorAndroid_jni.h"
 
 namespace content {
 
 namespace {
 const size_t kMBShift = 20;
 }
 
 // static
 std::unique_ptr<MemoryMonitorAndroid> MemoryMonitorAndroid::Create() {
   return base::WrapUnique(new MemoryMonitorAndroid);
 }
 
-MemoryMonitorAndroid::MemoryMonitorAndroid() {
-  InitializeFieldIDs();
+// static
+bool MemoryMonitorAndroid::Register(JNIEnv* env) {
+  return RegisterNativesImpl(env);
 }
 
+MemoryMonitorAndroid::MemoryMonitorAndroid() {}
+
 MemoryMonitorAndroid::~MemoryMonitorAndroid() {}
 
 int MemoryMonitorAndroid::GetFreeMemoryUntilCriticalMB() {
-  DCHECK(CanGetMemoryInfo());
   MemoryInfo info;
   GetMemoryInfo(&info);
   return (info.avail_mem - info.threshold) >> kMBShift;

[bashi, 2016/09/27 03:51:36]

agrieve@ gave me great advice not to call GetMemoryInfo() every time. I'll try
to reduce GetMemoryInfo() calls in a follow-up CL.

 }
 
-bool MemoryMonitorAndroid::CanGetMemoryInfo() {
-  return (avail_mem_id_ != 0 && low_memory_id_ != 0 && threshold_id_ != 0 &&
-          total_mem_id_ != 0);
+void MemoryMonitorAndroid::GetMemoryInfo(MemoryInfo* out) {
+  DCHECK(out);
+  JNIEnv* env = base::android::AttachCurrentThread();
+  Java_MemoryMonitorAndroid_getMemoryInfo(
+      env, base::android::GetApplicationContext(),
+      reinterpret_cast<intptr_t>(out));
 }
 
-void MemoryMonitorAndroid::GetMemoryInfo(MemoryInfo* out) {
-  DCHECK(out);
-  DCHECK(CanGetMemoryInfo());
-  JNIEnv* env = base::android::AttachCurrentThread();
-  base::android::ScopedJavaLocalRef<jobject> info =
-      Java_MemoryMonitorAndroid_getMemoryInfo(
-          env, base::android::GetApplicationContext());
-  out->avail_mem = env->GetLongField(info.obj(), avail_mem_id_);
-  out->low_memory = env->GetBooleanField(info.obj(), low_memory_id_);
-  out->threshold = env->GetLongField(info.obj(), threshold_id_);
-  out->total_mem = env->GetLongField(info.obj(), total_mem_id_);
-}
-
-void MemoryMonitorAndroid::InitializeFieldIDs() {
-  JNIEnv* env = base::android::AttachCurrentThread();
-  base::android::ScopedJavaLocalRef<jclass> clazz =
-      base::android::GetClass(env, "android/app/ActivityManager$MemoryInfo");
-  avail_mem_id_ = env->GetFieldID(clazz.obj(), "availMem", "J");
-  low_memory_id_ = env->GetFieldID(clazz.obj(), "lowMemory", "Z");
-  threshold_id_ = env->GetFieldID(clazz.obj(), "threshold", "J");
-  total_mem_id_ = env->GetFieldID(clazz.obj(), "totalMem", "J");
+// Called by JNI to populate ActivityManager.MemoryInfo.
+static void GetMemoryInfoCallback(
+    JNIEnv* env,
+    const base::android::JavaParamRef<jclass>& clazz,
+    jlong avail_mem,
+    jboolean low_memory,
+    jlong threshold,
+    jlong total_mem,
+    jlong out_ptr) {
+  DCHECK(out_ptr);
+  MemoryMonitorAndroid::MemoryInfo* info =
+      reinterpret_cast<MemoryMonitorAndroid::MemoryInfo*>(out_ptr);
+  info->avail_mem = avail_mem;
+  info->low_memory = low_memory;
+  info->threshold = threshold;
+  info->total_mem = total_mem;
 }
 
 // Implementation of a factory function defined in memory_monitor.h.
 std::unique_ptr<MemoryMonitor> CreateMemoryMonitor() {
   return MemoryMonitorAndroid::Create();
 }
 
 }  // namespace content