base/threading: Lazy thread startup for pthreads

base/threading/platform_thread_posix.cc

Index: base/threading/platform_thread_posix.cc
diff --git a/base/threading/platform_thread_posix.cc b/base/threading/platform_thread_posix.cc
index 95cc5d55cda76c2a0bd82e28700a5fc6de89dc78..da685d6aa51e92cc51958b31445cb23afa4361c7 100644
--- a/base/threading/platform_thread_posix.cc
+++ b/base/threading/platform_thread_posix.cc
@@ -36,23 +36,17 @@ namespace {
 
 struct ThreadParams {
   ThreadParams()
-      : delegate(NULL),
-        joinable(false),
-        priority(ThreadPriority::NORMAL),
-        handle(NULL),
-        handle_set(false, false) {
-  }
+      : delegate(NULL), joinable(false), priority(ThreadPriority::NORMAL) {}
 
   PlatformThread::Delegate* delegate;
   bool joinable;
   ThreadPriority priority;
-  PlatformThreadHandle* handle;
-  WaitableEvent handle_set;
 };
 
 void* ThreadFunc(void* params) {
+  CHECK(params);
   base::InitOnThread();
-  ThreadParams* thread_params = static_cast<ThreadParams*>(params);
+  scoped_ptr<ThreadParams> thread_params(static_cast<ThreadParams*>(params));
 
   PlatformThread::Delegate* delegate = thread_params->delegate;
   if (!thread_params->joinable)
@@ -61,11 +55,6 @@ void* ThreadFunc(void* params) {
   if (thread_params->priority != ThreadPriority::NORMAL)
     PlatformThread::SetCurrentThreadPriority(thread_params->priority);
 
-  // Stash the id in the handle so the calling thread has a complete
-  // handle, and unblock the parent thread.
-  *(thread_params->handle) = PlatformThreadHandle(pthread_self());
-  thread_params->handle_set.Signal();
-
   ThreadIdNameManager::GetInstance()->RegisterThread(
       PlatformThread::CurrentHandle().platform_handle(),
       PlatformThread::CurrentId());
@@ -80,21 +69,21 @@ void* ThreadFunc(void* params) {
   return NULL;
 }
 
-bool CreateThread(size_t stack_size, bool joinable,
+bool CreateThread(size_t stack_size,
+                  bool joinable,
                   PlatformThread::Delegate* delegate,
                   PlatformThreadHandle* thread_handle,
                   ThreadPriority priority) {
+  CHECK(thread_handle);
   base::InitThreading();
 
-  bool success = false;
   pthread_attr_t attributes;
   pthread_attr_init(&attributes);
 
   // Pthreads are joinable by default, so only specify the detached
   // attribute if the thread should be non-joinable.
-  if (!joinable) {
+  if (!joinable)
     pthread_attr_setdetachstate(&attributes, PTHREAD_CREATE_DETACHED);
-  }
 
   // Get a better default if available.
   if (stack_size == 0)
@@ -103,33 +92,29 @@ bool CreateThread(size_t stack_size, bool joinable,
   if (stack_size > 0)
     pthread_attr_setstacksize(&attributes, stack_size);
 
-  ThreadParams params;
-  params.delegate = delegate;
-  params.joinable = joinable;
-  params.priority = priority;
-  params.handle = thread_handle;
+  scoped_ptr<ThreadParams> params(new ThreadParams);
+  params->delegate = delegate;
+  params->joinable = joinable;
+  params->priority = priority;
 
   pthread_t handle;
-  int err = pthread_create(&handle,
-                           &attributes,
-                           ThreadFunc,
-                           &params);
-  success = !err;
-  if (!success) {
-    // Value of |handle| is undefined if pthread_create fails.
+  int err =
+      pthread_create(&handle, &attributes, ThreadFunc, params.get());
+  bool success = !err;
+  if (success) {
+    // ThreadParams should be deleted on the created thread after used.
+    ThreadParams* unused_params = params.release();
+    ALLOW_UNUSED_LOCAL(unused_params);

[kinuko, 2015/07/02 14:23:35]

nit: ignore_result(param.release()) would work

[Takashi Toyoshima, 2015/07/03 04:31:35]

Done.

+  } else {
+    // Value of |thread_handle| is undefined if pthread_create fails.

[Takashi Toyoshima, 2015/07/02 13:57:50]

Oops, self review note: s/thread_handle/handle/.

[Takashi Toyoshima, 2015/07/03 04:31:35]

Done.

     handle = 0;
     errno = err;
     PLOG(ERROR) << "pthread_create";
   }
+  *thread_handle = PlatformThreadHandle(handle);
 
   pthread_attr_destroy(&attributes);
 
-  // Don't let this call complete until the thread id
-  // is set in the handle.
-  if (success)
-    params.handle_set.Wait();
-  CHECK_EQ(handle, thread_handle->platform_handle());
-
   return success;
 }