base: Support setting thread priorities generically.

base/threading/platform_thread.h

Index: base/threading/platform_thread.h
diff --git a/base/threading/platform_thread.h b/base/threading/platform_thread.h
index 576695a4e7b5f8028f47cc5e02921b551ffb0a39..c5975000016cd54d573549f3ef36bc4255c29c8b 100644
--- a/base/threading/platform_thread.h
+++ b/base/threading/platform_thread.h
@@ -23,27 +23,66 @@
 
 namespace base {
 
-// PlatformThreadHandle should not be assumed to be a numeric type, since the
-// standard intends to allow pthread_t to be a structure.  This means you
-// should not initialize it to a value, like 0.  If it's a member variable, the
-// constructor can safely "value initialize" using () in the initializer list.
 #if defined(OS_WIN)
 typedef DWORD PlatformThreadId;
-typedef void* PlatformThreadHandle;  // HANDLE
-const PlatformThreadHandle kNullThreadHandle = NULL;
 #elif defined(OS_POSIX)
-typedef pthread_t PlatformThreadHandle;
-const PlatformThreadHandle kNullThreadHandle = 0;
 typedef pid_t PlatformThreadId;
 #endif
 
-const PlatformThreadId kInvalidThreadId = 0;
+class PlatformThreadHandle {
+ public:
+#if defined(OS_WIN)
+  typedef void* Handle;
+#elif defined(OS_POSIX)
+  typedef pthread_t Handle;
+#endif
+
+  PlatformThreadHandle()
+      : handle_(0),
+        id_(0) {
+  }
+
+  explicit PlatformThreadHandle(Handle handle)
+      : handle_(handle),
+        id_(0) {
+  }
+
+  PlatformThreadHandle(Handle handle,
+                       PlatformThreadId id)
+      : handle_(handle),
+        id_(id) {
+  }
+
+  bool is_equal(const PlatformThreadHandle& other) {
+    return handle_ == other.handle_;
+  }
+
+  bool is_null() {
+    return !handle_;
+  }
+
+  Handle platform_handle() {
+    return handle_;
+  }
+
+ private:
+  friend class PlatformThread;
+
+  Handle handle_;
+  PlatformThreadId id_;
+};
+
+const PlatformThreadId kInvalidThreadId(0);
 
 // Valid values for SetThreadPriority()
 enum ThreadPriority{
   kThreadPriority_Normal,
   // Suitable for low-latency, glitch-resistant audio.
-  kThreadPriority_RealtimeAudio
+  kThreadPriority_RealtimeAudio,
+  // Suitable for threads which generate data for the display (at ~60Hz).
+  kThreadPriority_Display,
+  // Suitable for threads that shouldn't disrupt high priority work.
+  kThreadPriority_Background
 };
 
 // A namespace for low-level thread functions.
@@ -62,6 +101,9 @@ class BASE_EXPORT PlatformThread {
   // Gets the current thread id, which may be useful for logging purposes.
   static PlatformThreadId CurrentId();
 
+  // Get the current handle.
+  static PlatformThreadHandle CurrentHandle();
+
   // Yield the current thread so another thread can be scheduled.
   static void YieldCurrentThread();
 
@@ -106,8 +148,6 @@ class BASE_EXPORT PlatformThread {
   // |thread_handle|.
   static void Join(PlatformThreadHandle thread_handle);
 
-  // Sets the priority of the thread specified in |handle| to |priority|.
-  // This does not work on Linux, use CreateWithPriority() instead.
   static void SetThreadPriority(PlatformThreadHandle handle,
                                 ThreadPriority priority);