[reland] Do not block in SimpleThread::Start().

base/threading/simple_thread.cc

Index: base/threading/simple_thread.cc
diff --git a/base/threading/simple_thread.cc b/base/threading/simple_thread.cc
index 9eb443afab1b5d5dcb3dcd7427f8c4a1faacbb1b..65a56f212e269f4eef60cb65615126ed494bedd2 100644
--- a/base/threading/simple_thread.cc
+++ b/base/threading/simple_thread.cc
@@ -18,17 +18,25 @@ SimpleThread::SimpleThread(const std::string& name_prefix,
                            const Options& options)
     : name_prefix_(name_prefix),
       options_(options),
-      event_(WaitableEvent::ResetPolicy::MANUAL,
-             WaitableEvent::InitialState::NOT_SIGNALED) {}
+      id_event_(WaitableEvent::ResetPolicy::MANUAL,
+                WaitableEvent::InitialState::NOT_SIGNALED) {}
 
 SimpleThread::~SimpleThread() {
-  DCHECK(HasBeenStarted()) << "SimpleThread was never started.";
-  DCHECK(!options_.joinable || HasBeenJoined())
+#if DCHECK_IS_ON()
+  DCHECK(has_been_started_) << "SimpleThread was never started.";
+  DCHECK(!options_.joinable || has_been_joined_)
       << "Joinable SimpleThread destroyed without being Join()ed.";
+#endif
 }
 
 void SimpleThread::Start() {
-  DCHECK(!HasBeenStarted()) << "Tried to Start a thread multiple times.";
+#if DCHECK_IS_ON()
+  DCHECK(!has_been_started_) << "Tried to Start a thread multiple times.";
+
+  // Set |has_been_started_| before creating the thread as no member access is
+  // allowed after.
+  has_been_started_ = true;
+#endif
   bool success =
       options_.joinable
           ? PlatformThread::CreateWithPriority(options_.stack_size, this,
@@ -36,35 +44,39 @@ void SimpleThread::Start() {
           : PlatformThread::CreateNonJoinableWithPriority(
                 options_.stack_size, this, options_.priority);
   DCHECK(success);
-  ThreadRestrictions::ScopedAllowWait allow_wait;
-  event_.Wait();  // Wait for the thread to complete initialization.
+
+  // No member access after creating the thread, |this| can be deleted at any
+  // point after invoking Run() on non-joinable threads.
 }
 
 void SimpleThread::Join() {
+#if DCHECK_IS_ON()
   DCHECK(options_.joinable) << "A non-joinable thread can't be joined.";
-  DCHECK(HasBeenStarted()) << "Tried to Join a never-started thread.";
-  DCHECK(!HasBeenJoined()) << "Tried to Join a thread multiple times.";
+  DCHECK(has_been_started_) << "Tried to Join a never-started thread.";
+  DCHECK(!has_been_joined_) << "Tried to Join a thread multiple times.";
+#endif
   PlatformThread::Join(thread_);
   thread_ = PlatformThreadHandle();
-  joined_ = true;
+#if DCHECK_IS_ON()
+  has_been_joined_ = true;
+#endif
 }
 
-bool SimpleThread::HasBeenStarted() {
-  ThreadRestrictions::ScopedAllowWait allow_wait;
-  return event_.IsSignaled();
+PlatformThreadId SimpleThread::GetTid() const {
+  id_event_.Wait();
+  return tid_;
 }
 
 void SimpleThread::ThreadMain() {
   tid_ = PlatformThread::CurrentId();
+  id_event_.Signal();
+
   // Construct our full name of the form "name_prefix_/TID".
   std::string name(name_prefix_);
   name.push_back('/');
   name.append(IntToString(tid_));
   PlatformThread::SetName(name);
 
-  // We've initialized our new thread, signal that we're done to Start().
-  event_.Signal();
-
   Run();
 }