Re: [Boost-bugs] [Boost C++ Libraries] #12220: Memory leak in future::then()

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #12220: Memory leak in future::then()
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2016-08-18 19:23:37

#12220: Memory leak in future::then()
-------------------------------+-------------------------------------
  Reporter:  valentin.milea@…  |      Owner:  viboes
      Type:  Bugs              |     Status:  assigned
 Milestone:  To Be Determined  |  Component:  thread
   Version:  Boost 1.61.0      |   Severity:  Regression
Resolution:                    |   Keywords:  memory leak future then
-------------------------------+-------------------------------------

Comment (by BloodyRookie):

 "static_shared_from_this(this) is used as parameter of the run function
 and the parameter is released when the function ends, isn't it?"

 Where is the parameter released?

 Suppose I have code like this

 {{{
 {
    auto f = boost::make_ready_future<int>(41).then([](boost::future<int>)
 { return 42; });
    f.get(); // wait for the future to complete
 }
 }}}

 Then at some point

 {{{
 this->thr_ = thread(&future_async_shared_state::run,
 static_shared_from_this(this), boost::forward<Fp>(f));
 }}}

 Is called. The thread ctor calls

 {{{
 thread_info(make_thread_info(boost::bind(boost::type<void>(),f,a1)))
 }}}

 a1 is

 boost::shared_ptr<boost::detail::future_async_continuation_shared_state<boost::future<int>,int,int
 <lambda>(boost::future<int>)>>

 The result of boost::bind is stored in the thread_data member (actually
 the pointer thread_data_ptr keeps it alive)

 After the future completes the situation has not changed, nothing is
 released imo.
 In the debugger I can see the following:

 http://imgur.com/a/7u5ii


 There are 2 strong references on the shared state, one is from the
 variable f but the other one is from the creation of the thread which is
 attached to the future.  The dtor of the future is never called.

 If I comment out the BOOST_THREAD_FUTURE_BLOCKING flag definition then at
 the same break point there is only 1 strong reference and the dtor of the
 future is called.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/12220#comment:6>
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