Boost C++ Libraries: Ticket #5432: Deadlock with thread group's join_all and other modifier methods.

Wed, 06 Apr 2011 14:17:56 GMT

Woops, I made a mistake on my test case. I never unlocked the mutex in run, and I never returned from main.

#include <boost/thread.hpp>
boost::mutex lock;
boost::thread * t[128];
boost::thread_group tg;
void run(int i) {
  lock.lock();
  // remove_thread locks the thread_group's mutex,
  // and join_all locks the thread_group's mutex
  // causing deadlock.
  tg.remove_thread(t[i]); // ***** Deadlock when tg.m is locked.
  lock.unlock();
}
int main() {
  lock.lock();
  for( int i = 0; i < 128; ++i ) {
    t[i] = new boost::thread(run,i);
    tg.add_thread(t[i]);
  }
  lock.unlock();
  tg.join_all(); // ***** Deadlock when tg.m is locked.
  return 0;
}

attachment set

Wed, 06 Apr 2011 21:01:34 GMT

attachment → thread_group.hpp

I revised the solution to the problem. The join all method will copy the current thread list. The join all method will then join all the current threads in the list. All modifications to the list will be ignored until join_all exits and is called again. Other solutions are welcome, but this is a classic reader-writer problem.

component changed

viboes — Wed, 11 May 2011 06:17:18 GMT

component threads → thread

owner, status changed; cc set

viboes — Sun, 04 Dec 2011 19:02:09 GMT

cc viboes added
owner changed from Anthony Williams to viboes
status new → assigned

Your examples is an example of deadlock, but I'm not sure if we can say that there is a deadlock in Boost.Thread.

Your solution seems to not be one, as the thread calling join-all will think that all the thread in the group are joined and this could be not the case as other thread could be added to it.

I think that the best the library can do is to move one thread group to another.

Maybe the documentation should stay that access to the thread group from any thread in the group will result in a deadlock.

type, severity changed

viboes — Wed, 07 Dec 2011 22:48:32 GMT

type Bugs → Support Requests
severity Showstopper → Problem

Moved to support request until resolution clarified.

status changed; resolution set

viboes — Sat, 07 Jan 2012 23:15:14 GMT

status assigned → closed
resolution → worksforme

Closed as the deadlock is not in the library. Please reopen if you don't agree with resolution.