base: Support setting thread priorities generically.

base/threading/platform_thread.h

 // Copyright (c) 2012 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.
 
 // WARNING: You should *NOT* be using this class directly.  PlatformThread is
 // the low-level platform-specific abstraction to the OS's threading interface.
 // You should instead be using a message-loop driven Thread, see thread.h.
 
 #ifndef BASE_THREADING_PLATFORM_THREAD_H_
 #define BASE_THREADING_PLATFORM_THREAD_H_
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/time.h"
 #include "build/build_config.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #elif defined(OS_POSIX)
 #include <pthread.h>
 #include <unistd.h>
 #endif
 
 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.
 class BASE_EXPORT PlatformThread {
  public:
   // Implement this interface to run code on a background thread.  Your
   // ThreadMain method will be called on the newly created thread.
   class BASE_EXPORT Delegate {
    public:
     virtual void ThreadMain() = 0;
 
    protected:
     virtual ~Delegate() {}
   };
 
   // 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();
 
   // Sleeps for the specified duration.
   static void Sleep(base::TimeDelta duration);
 
   // Sets the thread name visible to debuggers/tools. This has no effect
   // otherwise. This name pointer is not copied internally. Thus, it must stay
   // valid until the thread ends.
   static void SetName(const char* name);
@@ skipping 24 matching lines @@
   // CreateNonJoinable() does the same thing as Create() except the thread
   // cannot be Join()'d.  Therefore, it also does not output a
   // PlatformThreadHandle.
   static bool CreateNonJoinable(size_t stack_size, Delegate* delegate);
 
   // Joins with a thread created via the Create function.  This function blocks
   // the caller until the designated thread exits.  This will invalidate
   // |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);
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PlatformThread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_PLATFORM_THREAD_H_