Add support for real-time audio threads.

base/threading/platform_thread.h

Index: base/threading/platform_thread.h
===================================================================
--- base/threading/platform_thread.h	(revision 84711)
+++ base/threading/platform_thread.h	(working copy)
@@ -47,6 +47,13 @@
 
 const PlatformThreadId kInvalidThreadId = 0;
 
+// Valid values for SetThreadPriority()
+enum ThreadPriority{
+  kThreadPriority_Normal,
+  // Suitable for low-latency, glitch-resistant audio.
+  kThreadPriority_RealtimeAudio

[darin (slow to review), 2011/05/13 17:51:12]

isn't it a bit unfortunate for base to have to know about the concept of
real-time audio???

isn't there maybe some better way to parameterize this so that a consumer could
use PlatformThread APIs to construct a thread suitable for real-time audio?

[scherkus (not reviewing), 2011/05/13 23:06:49]

I don't want to bikeshed this anymore, but what about Normal and High?

...and if setting between high/normal doesn't make sense you *could* go all the
way with just having a "IncreaseThreadPriority()" method

[Ken Russell (switch to Gerrit), 2011/05/13 23:11:01]

The Mac implementation is currently very specific to the audio use case, and I
can imagine wanting to have a high-priority enum that's different from the audio
enum. This was the motivation for suggesting the audio specific enum.

+};
+
 // A namespace for low-level thread functions.
 class BASE_API PlatformThread {
  public:
@@ -91,6 +98,9 @@
   // |thread_handle|.
   static void Join(PlatformThreadHandle thread_handle);
 
+  static void SetThreadPriority(PlatformThreadHandle handle,

[scherkus (not reviewing), 2011/05/13 23:06:49]

could we get a comment + disclaimer here warning people not to carelessly bump
up the thread priority?

I think I linked you to the discussion before on chromium-dev:
http://groups.google.com/a/chromium.org/group/chromium-dev/browse_thread/thre...

+                                ThreadPriority priority);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
 };