Added automatic mode to FakeInputAudioStream to generate automatic beeps

media/audio/fake_audio_input_stream.cc

Index: media/audio/fake_audio_input_stream.cc
diff --git a/media/audio/fake_audio_input_stream.cc b/media/audio/fake_audio_input_stream.cc
index 5ec09a45c870b16995d0aaa1545beb9fe4e13d2e..c9107f1e19c791da8e44c47e2ec12401ad8bd8ec 100644
--- a/media/audio/fake_audio_input_stream.cc
+++ b/media/audio/fake_audio_input_stream.cc
@@ -20,10 +20,16 @@ namespace {
 const int kBeepDurationMilliseconds = 20;
 const int kBeepFrequency = 400;
 
+// Intervals between two automatic beeps.
+const int kAutomaticBeepIntervalInMs = 500;
+
+// Automatic beep will be triggered every |kAutomaticBeepIntervalInMs| unless
+// users explicitly call BeepOnce(), which will disable the automatic beep.
 struct BeepContext {
-  BeepContext() : beep_once(false) {}
+  BeepContext() : beep_once(false), automatic(true) {}

[DaleCurtis, 2014/04/29 17:30:56]

Shouldn't this default to false? Isn't this used in production for cases w/o a
mic?

[no longer working on chromium, 2014/05/02 14:30:47]

That is good point, I honestly have no idea how the fake input stream is used
for production.

My understanding is that, In production, when there is no mic, all the clients
won't pass the UI if they are requesting mic.

But I searched the code base and found out that in AudioManagerLinux, if no
cras, no pulse and no alsa, it will use FakeAudioManager:
#if defined(USE_ALSA)
  UMA_HISTOGRAM_ENUMERATION("Media.LinuxAudioIO", kAlsa, kAudioIOMax + 1);
  return new AudioManagerAlsa(audio_log_factory);
#else
  return new FakeAudioManager(audio_log_factory);
#endif
But I believe there is no way to make FakeAudioManager working in such case,
since it does not have any device:
bool FakeAudioManager::HasAudioOutputDevices() { return false; }
bool FakeAudioManager::HasAudioInputDevices() { return false; }

It is used in order to get things compiled.

I don't really want to add one more static method to enable the automatic beep,
so I added Alpha to double check if it OK to have the automatic as true by
default.

   base::Lock beep_lock;
   bool beep_once;
+  bool automatic;
 };
 
 static base::LazyInstance<BeepContext> g_beep_context =
@@ -78,14 +84,37 @@ void FakeAudioInputStream::Start(AudioInputCallback* callback)  {
 void FakeAudioInputStream::DoCallback() {
   DCHECK(callback_);
 
+  const TimeTicks now = TimeTicks::Now();
+  base::TimeDelta next_callback_time =
+      last_callback_time_ + callback_interval_ * 2 - now;
+
+  // If we are falling behind, try to catch up as much as we can in the next
+  // callback.
+  if (next_callback_time < base::TimeDelta())
+    next_callback_time = base::TimeDelta();
+
+  // Accumulate the time from the last beep.
+  interval_from_last_beep_ += now - last_callback_time_;
+
+  last_callback_time_ = now;
+
   memset(buffer_.get(), 0, buffer_size_);
 
   bool should_beep = false;
   {
     BeepContext* beep_context = g_beep_context.Pointer();
     base::AutoLock auto_lock(beep_context->beep_lock);
-    should_beep = beep_context->beep_once;
-    beep_context->beep_once = false;
+    if (beep_context->automatic) {
+      int delta_ms = interval_from_last_beep_.InMilliseconds() -
+          kAutomaticBeepIntervalInMs;
+      if (delta_ms > 0) {

[DaleCurtis, 2014/04/29 17:30:56]

just use > base::TimeDelta to avoid converting back and forth.

[no longer working on chromium, 2014/05/02 14:30:47]

Done.

+        should_beep = true;
+        interval_from_last_beep_ =  TimeDelta::FromMilliseconds(delta_ms);
+      }
+    } else {
+      should_beep = beep_context->beep_once;
+      beep_context->beep_once = false;
+    }
   }
 
   // If this object was instructed to generate a beep or has started to
@@ -103,7 +132,6 @@ void FakeAudioInputStream::DoCallback() {
     while (position + high_bytes <= buffer_size_) {
       // Write high values first.
       memset(buffer_.get() + position, 128, high_bytes);
-
       // Then leave low values in the buffer with |high_bytes|.
       position += high_bytes * 2;
     }
@@ -116,16 +144,6 @@ void FakeAudioInputStream::DoCallback() {
   callback_->OnData(this, buffer_.get(), buffer_size_, buffer_size_, 1.0);
   frames_elapsed_ += params_.frames_per_buffer();
 
-  const TimeTicks now = TimeTicks::Now();
-  base::TimeDelta next_callback_time =
-      last_callback_time_ + callback_interval_ * 2 - now;
-
-  // If we are falling behind, try to catch up as much as we can in the next
-  // callback.
-  if (next_callback_time < base::TimeDelta())
-    next_callback_time = base::TimeDelta();
-
-  last_callback_time_ = now;
   thread_.message_loop()->PostDelayedTask(
       FROM_HERE,
       base::Bind(&FakeAudioInputStream::DoCallback, base::Unretained(this)),
@@ -163,6 +181,7 @@ void FakeAudioInputStream::BeepOnce() {
   BeepContext* beep_context = g_beep_context.Pointer();
   base::AutoLock auto_lock(beep_context->beep_lock);
   beep_context->beep_once = true;
+  beep_context->automatic = false;
 }
 
 }  // namespace media