It is not guaranteed.. -Vamsi -----Original Message----- From: linux-c-programming-owner@xxxxxxxxxxxxxxx [mailto:linux-c-programming-owner@xxxxxxxxxxxxxxx] On Behalf Of Sreevathsa Sent: Thursday, March 15, 2007 12:43 PM To: linux-c-programming@xxxxxxxxxxxxxxx Subject: PThread question I have a question on syncing the threads. I have a scenario like this: 5 threads (T1, T2, T3, T4 & T5) are working on this piece of code: LINE1: for(;;) { LINE2: pthread_mutex_lock(&r1_mutex) LINE3: ............. LINE4: ............. LINE5: pthread_mutex_unlock(&r1_mutex) /* some code that does not need protection */ LINE6: ............. LINE7: ............. LINE8: pthread_mutex_lock(&r2_mutex) LINE9: ............. LINE10: ............. LINE11: pthread_mutex_unlock(&r2_mutex) LINE12: } r1_mutex is to protect the access to a FIFO queue. I want the 5 threads to process the queue contents in the same order in which they arrived into the queue. Now, lets assume that a request comes into the queue and thread T1 picks up and starts processing it. T1 has released r1_mutex lock and is holding r2_mutex lock and is executing the code in lines 9 and 10. While T1 is busy executing code on lines 9 and 10, the queue gets 4 more requests and threads T2, T3, T4 and T5 (in that order) picks each one of them in the order in which they came into the queue and start processing them. They come till LINE 8 and wait to lock r2_mutex which thread T1 has currently locked. Now, given this scenario, here is my question: After T1 unlocks r2_mutex, which thread among T2, T3, T4 and T5 gets the r2_mutex lock? Does pthread scheduler schedule (give the lock to) thread T2 which came to LINE8 first?? FYI: I use Linux 2.6 - Fedora distro. I am not sure if its uses NPTL or the native Linux threads. Thanks, Sreevathsa - To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-c-programming" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
