RefCountInterface: Make AddRef() and Release() const

This CL makes AddRef() and Release() const member methods and the refcount integer mutable. This is reasonable, because they only manage the lifetime of the object, and this is also how it's done in Chromium.

The purpose is to be able to capture a const pointer in a scoped_refptr, which is currenty impossible. The practial problem this CL solves is this:

void Foo::Bar() const {}

rtc::Callback0<void> Foo::MakeClosure() const {
  return rtc::Bind(&Foo::Bar, this);
}

We currently capture |this| as const Foo*. With this CL, |this| will be captured as scoped_refptr<const Foo>.

A test is also added in bind_unittest to check this behaviour.

BUG=webrtc:5065
R=perkj@webrtc.org, tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1403683004 .

Cr-Commit-Position: refs/heads/master@{#10253}

talk/app/webrtc/dtmfsender_unittest.cc

@@ -34,6 +34,7 @@
 #include "talk/app/webrtc/audiotrack.h"
 #include "webrtc/base/gunit.h"
 #include "webrtc/base/logging.h"
+#include "webrtc/base/refcount.h"
 #include "webrtc/base/timeutils.h"
 
 using webrtc::AudioTrackInterface;
@@ -45,7 +46,7 @@ using webrtc::DtmfSenderObserverInterface;
 static const char kTestAudioLabel[] = "test_audio_track";
 static const int kMaxWaitMs = 3000;
 
-class FakeDtmfObserver : public DtmfSenderObserverInterface {
+class FakeDtmfObserver : public DtmfSenderObserverInterface, RefCountInterface {
  public:
   FakeDtmfObserver() : completed_(false) {}
 

talk/media/webrtc/fakewebrtcvideocapturemodule.h

@@ -101,8 +101,8 @@ class FakeWebRtcVideoCaptureModule : public webrtc::VideoCaptureModule {
       const webrtc::VideoCodec& codec) override {
     return NULL;  // not implemented
   }
-  int32_t AddRef() override { return 0; }
-  int32_t Release() override {
+  int32_t AddRef() const override { return 0; }
+  int32_t Release() const override {
     delete this;
     return 0;
   }

webrtc/base/bind_unittest.cc

@@ -108,6 +108,7 @@ EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(F);
 EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(RefCountedObject<RefCountInterface>);
 EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(RefCountedObject<B>);
 EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(RefCountedObject<C>);
+EXPECT_IS_CAPTURED_AS_SCOPED_REFPTR(const RefCountedObject<RefCountInterface>);
 
 TEST(BindTest, BindToMethod) {
   MethodBindTester object = {0};

webrtc/base/refcount.h

@@ -20,8 +20,8 @@ namespace rtc {
 // Reference count interface.
 class RefCountInterface {
  public:
-  virtual int AddRef() = 0;
-  virtual int Release() = 0;
+  virtual int AddRef() const = 0;
+  virtual int Release() const = 0;
  protected:
   virtual ~RefCountInterface() {}
 };
@@ -95,11 +95,11 @@ class RefCountedObject : public T {
   : T(p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11), ref_count_(0) {
   }
 
-  virtual int AddRef() {
+  int AddRef() const override {
     return AtomicOps::Increment(&ref_count_);
   }
 
-  virtual int Release() {
+  int Release() const override {
     int count = AtomicOps::Decrement(&ref_count_);
     if (!count) {
       delete this;
@@ -121,7 +121,7 @@ class RefCountedObject : public T {
   virtual ~RefCountedObject() {
   }
 
-  volatile int ref_count_;
+  mutable volatile int ref_count_;
 };
 
 }  // namespace rtc

webrtc/modules/audio_device/include/fake_audio_device.h

@@ -16,8 +16,8 @@ class FakeAudioDeviceModule : public AudioDeviceModule {
  public:
   FakeAudioDeviceModule() {}
   virtual ~FakeAudioDeviceModule() {}
-  virtual int32_t AddRef() { return 0; }
-  virtual int32_t Release() { return 0; }
+  virtual int32_t AddRef() const { return 0; }
+  virtual int32_t Release() const { return 0; }
   virtual int32_t RegisterEventObserver(AudioDeviceObserver* eventCallback) {
     return 0;
   }

webrtc/modules/interface/module.h

@@ -64,13 +64,13 @@ class RefCountedModule : public Module {
  public:
   // Increase the reference count by one.
   // Returns the incremented reference count.
-  virtual int32_t AddRef() = 0;
+  virtual int32_t AddRef() const = 0;
 
   // Decrease the reference count by one.
   // Returns the decreased reference count.
   // Returns 0 if the last reference was just released.
   // When the reference count reaches 0 the object will self-destruct.
-  virtual int32_t Release() = 0;
+  virtual int32_t Release() const = 0;
 
  protected:
   ~RefCountedModule() override = default;

webrtc/modules/video_capture/include/mock/mock_video_capture.h

@@ -22,8 +22,8 @@ class MockVideoCaptureModule : public VideoCaptureModule {
   MOCK_METHOD0(Process, int32_t());
 
   // from RefCountedModule
-  MOCK_METHOD0(AddRef, int32_t());
-  MOCK_METHOD0(Release, int32_t());
+  MOCK_CONST_METHOD0(AddRef, int32_t());
+  MOCK_CONST_METHOD0(Release, int32_t());
 
   // from VideoCaptureModule
   MOCK_METHOD1(RegisterCaptureDataCallback,

webrtc/system_wrappers/interface/ref_count.h

@@ -61,11 +61,11 @@ class RefCountImpl : public T {
   RefCountImpl(P1 p1, P2 p2, P3 p3, P4 p4, P5 p5)
       : T(p1, p2, p3, p4, p5), ref_count_(0) {}
 
-  virtual int32_t AddRef() {
+  int32_t AddRef() const override {
     return ++ref_count_;
   }
 
-  virtual int32_t Release() {
+  int32_t Release() const override {
     int32_t ref_count;
     ref_count = --ref_count_;
     if (ref_count == 0)
@@ -74,7 +74,7 @@ class RefCountImpl : public T {
   }
 
  protected:
-  Atomic32 ref_count_;
+  mutable Atomic32 ref_count_;
 };
 
 }  // namespace webrtc