PlatformThreadHandle: remove public id() interface

base/threading/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.
 
 #ifndef BASE_THREADING_THREAD_H_
 #define BASE_THREADING_THREAD_H_
 
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 152 matching lines @@
   scoped_refptr<SingleThreadTaskRunner> task_runner() const {
     return message_loop_ ? message_loop_->task_runner() : nullptr;
   }
 
   // Returns the name of this thread (for display in debugger too).
   const std::string& thread_name() const { return name_; }
 
   // The native thread handle.
   PlatformThreadHandle thread_handle() { return thread_; }
 
-  // The thread ID.
+  // The thread ID. Only valid after this Thread was started.
   PlatformThreadId thread_id() const;
 
   // Returns true if the thread has been started, and not yet stopped.
   bool IsRunning() const;
 
  protected:
   // Called just prior to starting the message loop
   virtual void Init() {}
 
   // Called to start the message loop
@@ skipping 21 matching lines @@
   // PlatformThread::Delegate methods:
   void ThreadMain() override;
 
 #if defined(OS_WIN)
   // Whether this thread needs to initialize COM, and if so, in what mode.
   ComStatus com_status_;
 #endif
 
   // If true, we're in the middle of stopping, and shouldn't access
   // |message_loop_|. It may non-NULL and invalid.
+  // Should be written on the thread that creates this thread. Also read data
+  // could be wrong on other threads.
   bool stopping_;
 
   // True while inside of Run().
   bool running_;
-  mutable base::Lock running_lock_;  // Protects running_.
 
   // The thread's handle.
   PlatformThreadHandle thread_;
-  mutable base::Lock thread_lock_;  // Protects thread_.
+
+  // The thread's id once it was started.
+  PlatformThreadId id_;
+
+  // Protects |running_|, |thread_|, and |id_|.

[kinuko, 2015/07/16 00:50:37]

nit: This no longer protects thread_?

nit: Unless the protected fields have close relationships or we have very severe
memory limit I prefer using separate locks for each field.

[Takashi Toyoshima, 2015/07/16 05:07:31]

Ah, good catch. It's true from the last patch set.

I changed to share one lock because gab@ suggested in the previous review, but
I'd follow kinuko's suggestion in the next patch set unless base/ owner object
it. Since kinuko is a content/ owner that is one of the most authoritative part
in chrome.

[Takashi Toyoshima, 2015/07/16 08:12:38]

So one reason to use a separate lock for id_ is that thread_id() is called from
many places for DCHECK and so on. So, sharing lock can easily introduce
recursive lock on changing this class.

+  mutable base::Lock lock_;
 
   // The thread's message loop.  Valid only while the thread is alive.  Set
   // by the created thread.
   MessageLoop* message_loop_;
 
   // Stores Options::timer_slack_ until the message loop has been bound to
   // a thread.
   TimerSlack message_loop_timer_slack_;
 
   // The name of the thread.  Used for debugging purposes.
   std::string name_;
 
   // Non-null if the thread has successfully started.
   scoped_ptr<WaitableEvent> start_event_;
 
   friend void ThreadQuitHelper();
 
   DISALLOW_COPY_AND_ASSIGN(Thread);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_THREAD_H_