id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
10478	Data race in boost/thread/future.hpp	Alexander Karzhenkov <karzhenkov@…>	viboes	"Non-static member function ""mark_finished_with_result"" of class template ""future_async_shared_state"" (inherited from ""future_async_shared_state_base"") is called from static member function ""run"" concurrently with constructor. Newly created thread uses the object being constructed by original thread. This is data race condition and results in undefined behavior [1.10.21, std-2011]. Moreover, the call of ""mark_finished_with_result"" may be completed even before constructor execution begins, which also leads to undefined behavior [12.7.1, std-2011].[[BR]]

Program below illustrates the problem:[[BR]]

{{{
#define BOOST_THREAD_VERSION 4

#include <iostream>
#include <boost/thread.hpp>

void func(int num)
{
	//boost::this_thread::yield();
	if (num == 0) return;
	std::cout << 'A' << num << std::endl;
	async(boost::launch::async, func, num - 1);
	std::cout << 'B' << num << std::endl;
}

int main()
{
	func(3);
}
}}}
Under QNX 6.5.0 SP1 with gcc 4.8.3 it gives the following:[[BR]]

{{{
A3
A2
A1
In function notify_all -- d:/boost_1_56_0/boost/thread/pthread/condition_variable.hpp:142 !pthread_cond_broadcast(&cond) -- assertion failed
}}}
After uncommenting the call of yield we get what’s expected:[[BR]]

{{{
A3
A2
A1
B1
B2
B3
}}}
Possible solution for C++11 is to create new thread in the body of ""future_async_shared_state"" constructor instead of using member initializer syntax for base:
{{{
--- future.hpp	Mon Aug  4 00:58:54 2014
+++ future-fixed.hpp	Thu Sep  4 13:00:54 2014
@@ -882,5 +882,5 @@
         public:
-          explicit future_async_shared_state(BOOST_THREAD_FWD_REF(Fp) f) :
-          base_type(thread(&future_async_shared_state::run, this, boost::forward<Fp>(f)))
+          explicit future_async_shared_state(BOOST_THREAD_FWD_REF(Fp) f)
           {
+            thr_ = thread(&future_async_shared_state::run, this, boost::forward<Fp>(f));
           }
@@ -912,5 +912,5 @@
         public:
-          explicit future_async_shared_state(BOOST_THREAD_FWD_REF(Fp) f) :
-          base_type(thread(&future_async_shared_state::run, this, boost::forward<Fp>(f)))
+          explicit future_async_shared_state(BOOST_THREAD_FWD_REF(Fp) f)
           {
+            thr_ = thread(&future_async_shared_state::run, this, boost::forward<Fp>(f));
           }
}}}
"	Bugs	closed	Boost 1.57.0	thread	Boost 1.56.0	Problem	fixed	future, shared state