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>
+#include <ostream>

[jar (doing other things), 2013/05/15 02:18:36]

nit: probably alphabetize by placing before line 20.

[epennerAtGoogle, 2013/05/15 05:09:08]

Done. I actually removed this.

[epenner, 2013/05/17 19:18:13]

I went ahead and removed this.

 #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;
+struct PlatformThreadHandle {

[jar (doing other things), 2013/05/15 02:18:36]

nit: this should probably be a class.

You'll probably want a copy constructors and such.

[epennerAtGoogle, 2013/05/15 05:09:08]

I made it a class to protect members, but default copy seems okay?

[epenner, 2013/05/17 19:18:13]

I made it into a class to protect private members, but default copy constructor
etc. is fine?

+  PlatformThreadHandle()
+    : handle(),
+      id(0) {
+  }
+
+  PlatformThreadHandle(pthread_t handle)

[jar (doing other things), 2013/05/15 02:18:36]

nit: explicit.

[epennerAtGoogle, 2013/05/15 05:09:08]

Done.

[epenner, 2013/05/17 19:18:13]

Done.

+    : handle(handle),
+      id(0) {
+  }
+
+  PlatformThreadHandle(pthread_t handle,
+                       PlatformThreadId id)
+    : handle(handle),
+      id(id) {
+  }
+
+  operator bool() const {
+    return !!handle;
+  }
+
+  bool operator!() {

[jar (doing other things), 2013/05/15 02:18:36]

Instead of operator overload, use method names, like IsNull()

[epennerAtGoogle, 2013/05/15 05:09:08]

I couldn't do this because the handle on windows was an integer type. So I have
now refactored windows also uses this container (and changed all call sites).

Done.

+    return !handle;
+  }
+
+  bool operator==(const PlatformThreadHandle& other) {

[jar (doing other things), 2013/05/15 02:18:36]

nit: again, just define a method name.

[epennerAtGoogle, 2013/05/15 05:09:08]

Done.

+    return handle == other.handle;
+  }
+
+  bool operator!=(const PlatformThreadHandle& other) {
+    return handle != other.handle;
+  }
+
+  pthread_t handle;
+  PlatformThreadId id;
+};
+
+const PlatformThreadHandle kNullThreadHandle(0);
+std::ostream& operator<< (std::ostream &out,

[jar (doing other things), 2013/05/15 02:18:36]

This is pretty uncommon, as use of streams is not generally endorsed.  Why did
you add this? To help with CHECK_*() calls?

[epennerAtGoogle, 2013/05/15 05:09:08]

Yes, I'm trying to remove it by changing a few call-sites.

+                          const PlatformThreadHandle& handle);
+
 #endif
 
 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_