Add |joinable| to Thread::Options

base/threading/thread.h

Index: base/threading/thread.h
diff --git a/base/threading/thread.h b/base/threading/thread.h
index 720ba8b6be80755e4ea833c1cd18d9f7193bbed2..e15a243b1b022586a162886187a32290e498f7a9 100644
--- a/base/threading/thread.h
+++ b/base/threading/thread.h
@@ -74,6 +74,12 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
 
     // Specifies the initial thread priority.
     ThreadPriority priority = ThreadPriority::NORMAL;
+
+    // If false, the thread will not be joined on destruction. This is intended
+    // for threads that want TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN
+    // semantics. Stop() will not be synchronous and will instead merely have
+    // StopSoon() semantics on such threads.
+    bool joinable = true;
   };
 
   // Constructor.
@@ -131,12 +137,14 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
   // carefully for production code.
   bool WaitUntilThreadStarted() const;
 
-  // Signals the thread to exit and returns once the thread has exited.  After
-  // this method returns, the Thread object is completely reset and may be used
-  // as if it were newly constructed (i.e., Start may be called again).
+  // Signals the thread to exit and returns once the thread has exited (or right

[danakj, 2016/07/22 21:00:40]

A thought: what if we made it illegal to call Stop on non-joinable threads and
you must use StopSoon instead?

[gab, 2016/07/25 16:07:40]

That was my first instinct too, but then I realized that Stop() is called by the
destructor and there is a strongly documented contract that any subclass must
also call Stop() in its destructor (ref. ~Thread() above). Therefore Stop() must
be defined and do the right thing for non-joinable threads.

+  // away if the thread is non-joinable).  For joinable threads only: after this
+  // method returns, the Thread object is completely reset and may be used as if
+  // it were newly constructed (i.e., Start may be called again) -- non-joinable
+  // threads are not re-usable.
   //
   // Stop may be called multiple times and is simply ignored if the thread is
-  // already stopped.
+  // already stopped or currently stopping.
   //
   // NOTE: If you are a consumer of Thread, it is not necessary to call this
   // before deleting your Thread objects, as the destructor will do it.