From ce535a9685b11c846560cc0f9f4dded1ca558efc Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Tue, 29 Sep 2015 13:54:05 +0100
Subject: Reduce space and time overhead of std::thread

	PR libstdc++/65393
	* config/abi/pre/gnu.ver: Export new symbols.
	* include/std/thread (thread::_State, thread::_State_impl): New types.
	(thread::_M_start_thread): Add overload taking unique_ptr<_State>.
	(thread::_M_make_routine): Remove.
	(thread::_S_make_state): Add.
	(thread::_Impl_base, thread::_Impl, thread::_M_start_thread)
	[_GLIBCXX_THREAD_ABI_COMPAT] Only declare conditionally.
	* src/c++11/thread.cc (execute_native_thread_routine): Rename to
	execute_native_thread_routine_compat and re-define to use _State.
	(thread::_State::~_State()): Define.
	(thread::_M_make_thread): Define new overload.
	(thread::_M_make_thread) [_GLIBCXX_THREAD_ABI_COMPAT]: Only define old
	overloads conditionally.

From-SVN: r228242
---
 libstdc++-v3/src/c++11/thread.cc | 47 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 45 insertions(+), 2 deletions(-)

(limited to 'libstdc++-v3/src')

diff --git a/libstdc++-v3/src/c++11/thread.cc b/libstdc++-v3/src/c++11/thread.cc
index 906cafa..e116afa 100644
--- a/libstdc++-v3/src/c++11/thread.cc
+++ b/libstdc++-v3/src/c++11/thread.cc
@@ -23,6 +23,7 @@
 // <http://www.gnu.org/licenses/>.
 
 
+#define _GLIBCXX_THREAD_ABI_COMPAT 1
 #include <thread>
 #include <system_error>
 #include <cerrno>
@@ -75,8 +76,33 @@ namespace std _GLIBCXX_VISIBILITY(default)
     extern "C" void*
     execute_native_thread_routine(void* __p)
     {
+      thread::_State_ptr __t{ static_cast<thread::_State*>(__p) };
+
+      __try
+	{
+	  __t->_M_run();
+	}
+      __catch(const __cxxabiv1::__forced_unwind&)
+	{
+	  __throw_exception_again;
+	}
+      __catch(...)
+	{
+	  std::terminate();
+	}
+
+      return nullptr;
+    }
+
+#if _GLIBCXX_THREAD_ABI_COMPAT
+    extern "C" void*
+    execute_native_thread_routine_compat(void* __p)
+    {
       thread::_Impl_base* __t = static_cast<thread::_Impl_base*>(__p);
       thread::__shared_base_type __local;
+      // Now that a new thread has been created we can transfer ownership of
+      // the thread state to a local object, breaking the reference cycle
+      // created in thread::_M_start_thread.
       __local.swap(__t->_M_this_ptr);
 
       __try
@@ -94,10 +120,13 @@ namespace std _GLIBCXX_VISIBILITY(default)
 
       return nullptr;
     }
+#endif
   }
 
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
+  thread::_State::~_State() = default;
+
   void
   thread::join()
   {
@@ -127,6 +156,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   }
 
   void
+  thread::_M_start_thread(_State_ptr state, void (*)())
+  {
+    const int err = __gthread_create(&_M_id._M_thread,
+				     &execute_native_thread_routine,
+				     state.get());
+    if (err)
+      __throw_system_error(err);
+    state.release();
+  }
+
+#if _GLIBCXX_THREAD_ABI_COMPAT
+  void
   thread::_M_start_thread(__shared_base_type __b)
   {
     if (!__gthread_active_p())
@@ -144,15 +185,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   thread::_M_start_thread(__shared_base_type __b, void (*)())
   {
     auto ptr = __b.get();
+    // Create a reference cycle that will be broken in the new thread.
     ptr->_M_this_ptr = std::move(__b);
     int __e = __gthread_create(&_M_id._M_thread,
-			       &execute_native_thread_routine, ptr);
+			       &execute_native_thread_routine_compat, ptr);
     if (__e)
     {
-      ptr->_M_this_ptr.reset();
+      ptr->_M_this_ptr.reset();  // break reference cycle, destroying *ptr.
       __throw_system_error(__e);
     }
   }
+#endif
 
   unsigned int
   thread::hardware_concurrency() noexcept
-- 
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