I would think the best way to synchronize this type of operation, where you want all the threads to "wait until it we are all ready" is via boost::barrier.
-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Sohail Somani Sent: Friday, January 12, 2007 12:39 PM To: boost@lists.boost.org Subject: [boost] [Threads] uncoditional scoped lock?
Hi,
Somewhat longer-than-normal-noise follows :)
Consider the following pseudo-code which has a race condition:
condition g_some_cond; mutex g_condition_mtx;
void thread_fn() { { ... // get lock g_some_cond.wait(condition_lock); } // do work }
void main_thread() { thread_group grp; // Start all threads and have them wait on the condition for(i in [0,N)) grp.create_thread(&thread_fn);
{ ... // get lock g_some_cond.notify_all(); // let threads continue } }
The race condition is of course that it is possible that not all threads actually start waiting on the condition before notify_all() is called. In this case, it is possible to solve the race condition in two ways:
1) Have the last thread that reaches the condition wait, signal to the main thread 2) Have the main thread checking the condition before notify_all()
I don't really like the first case because it requires bi-directional signalling between the threads. Though in my ignorance, I really do consider it the correct solution. The second solution would look something like this:
while(true) { scoped_lock cond_lock(g_condition_mtx); // .num_waiting_threads() is made up if(N_EXPECTED_THREADS==g_some_cond.num_waiting_threads()){break;} // release lock }
Should the second pattern be encapsulated in the condition object somehow? It is almost like timed_wait(mtx,xt,pred) but there is no timeout. So maybe untimed_wait()? Is there another way to do this?
Thanks for your eyes!
Sohail _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost