I have built a C++ library using boost ASIO. The library needs to be both thread-safe and fork-safe. It has service scheduler thread, which calls "_io_service.run())". To support fork-safety, I've registered pre_fork, post_fork_parent and post_fork_child handlers. The pre_fork() handler, calls "_io_service.notify_fork(boost::io_service:fork_prepare();", post_fork_parent handler calls "_io_service.notify_fork(boost::asio::io_service::fork_parent);" and post_fork_child calls "_io_service.notify_fork(boost::asio::io_service::fork_child);". The problem I'm facing in, when the fork() happens, the service scheduler thread might be in middle of some operation and might have acquired lock on data members of io_service object. So, the child process seems them in the same state and in the post_fork_child() when we call "_io_service.notify_fork(boost::asio::io_service::fork_child);" it tries to acquire the lock on the same object and hence get blocked indefinitely (as there is no thread in child to release the lock). The stack trace I see in the child process, which is blocked, is - fffffd7ffed07577 lwp_park (0, 0, 0) fffffd7ffecffc18 mutex_lock_internal () + 378 fffffd7ffecfffb2 mutex_lock_impl () + 112 fffffd7ffed0007b mutex_lock () + b fffffd7fff26419d __1cFboostEasioGdetailLscoped_lock4n0CLposix_mutex__2t5B6Mrn0D__v_ () + 1d fffffd7fff2866a2 __1cFboostEasioGdetailQdev_poll_reactorMfork_service6Mn0BKio_serviceKfork_event__v_ () + 32 fffffd7fff278527 __1cFboostEasioGdetailQservice_registryLnotify_fork6Mn0BKio_serviceKfork_event__v_ () + 107 fffffd7fff27531c __1cDdesGtunnelQServiceSchedulerPpost_fork_child6M_v_ () + 1c fffffd7fff29de24 post_fork_child () + 84 fffffd7ffec92188 _postfork_child_handler () + 38 fffffd7ffecf917d fork () + 12d fffffd7ffec172d5 fork () + 45 fffffd7ffef94309 fork () + 9 000000000043299d main () + 67d 0000000000424b2c ???????? () Apparently the "dev_poll_reactor" is locked (because it seems to be dispatching some pending events) in the service scheduler thread when the fork has happened which is causing the problem. I think to solve the problem, I need to ensure that service scheduler thread is not in the middle of any processing when the fork happens and one way to guarantee that would be to call "io_service.stop()" in pre_fork() handler but that doesn't sound like a good solution. Could you please let me know what is the right approach to make the library fork safe? The code snippets looks something like this. /** * Combines Boost.ASIO with a thread for scheduling. */ class ServiceScheduler : private boost::noncopyable { public : /// The actual thread used to perform work. boost::shared_ptr<boost::thread> _service_thread; /// Service used to manage async I/O events boost::asio::io_service _io_service; /// Work object to block the ioservice thread. std::auto_ptr<boost::asio::io_service::work> _work; ... }; /** * CTOR */ ServiceScheduler::ServiceScheduler() : _logger("ServiceScheduler"), _io_service(), _work(std::auto_ptr<boost::asio::io_service::work>( new boost::asio::io_service::work(_io_service))), _is_running(false) { } /** * Starts a thread to run async I/O service to process the scheduled work. */ void ServiceScheduler::start() { ScopedLock scheduler_lock(_mutex); if (!_is_running) { _is_running = true; _service_thread = boost::shared_ptr<boost::thread>( new boost::thread(boost::bind( &ServiceScheduler::processServiceWork, this))); } } /** * Processes work passed to the ASIO service and handles uncaught * exceptions */ void ServiceScheduler::processServiceWork() { try { std::cout<<"Running io_service"<<std::endl; _io_service.run(); } catch (std::exception& e) { TUNNEL_LOGGER_ERROR(_logger, "Exception while running ioservice" << e.what()); } catch (...) { TUNNEL_LOGGER_ERROR(_logger, "Uncaught exception while running " << "ioservice"); } } /** * Pre-fork handler */ void ServiceScheduler::pre_fork() { _io_service.notify_fork(boost::asio::io_service::fork_prepare); } /** * Post-fork parent handler */ void ServiceScheduler::post_fork_parent() { _io_service.notify_fork(boost::asio::io_service::fork_parent); } /** * Post-fork child handler */ void ServiceScheduler::post_fork_child() { _io_service.notify_fork(boost::asio::io_service::fork_child); } I'm using boost 1.47 and running the application on Solaris i386. The library and application are built using studio-12.0. Thanks Ranadheer -- View this message in context: http://boost.2283326.n4.nabble.com/How-to-make-boost-asio-fork-safe-tp440406... Sent from the Boost - Users mailing list archive at Nabble.com.