On 03/28/2018 11:32 AM, Pintu Kumar wrote: > On Wed, Mar 28, 2018 at 1:42 PM, Philippe Gerum <[email protected]> wrote: >> On 03/28/2018 09:54 AM, Pintu Kumar wrote: >>> Hi, >>> >>> We are facing one issue on Xenomai-3 on x86_64 system. >>> Kernel: 4.9.51 >>> ipipe version: 4 >>> # /usr/xenomai/sbin/version >>> Xenomai/cobalt v3.0.6 -- #5956064 (2018-03-20 12:13:33 +0100) >>> >>> Its a very simple API level test. >>> We create a condition variable and wait for the condition inside a task. >>> Then, we immediately signal the condition from the main thread, and simply >>> wait for the test to finish. >>> >>> But we observed that condition task is never getting released, and the >>> program hangs. >>> >>> This is the output: >>> -------------------------- >>> # ./condsignal >>> cond_task --> started >>> main --> cond signal success: 0 >>> Waiting for task to finish.... >>> ^C >>> >>> >>> This is the code snippet that was used. >>> ----------------------------------------------------- >>> # cat condsignal.c >>> >>> /* >>> * 1. Create an condition variable and wait inside a task. >>> * 2. Delete the condition variable from main task. >>> * 3. Observe that the condition wait is released and task ends normally. >>> * 4. Finally main task should exit normally. >>> * >>> * */ >>> #include <stdio.h> >>> #include <stdlib.h> >>> #include <sys/mman.h> >>> #include <alchemy/task.h> >>> #include <alchemy/mutex.h> >>> #include <alchemy/cond.h> >>> #include <alchemy/task.h> >>> >>> static RT_COND cond; >>> static RT_MUTEX mutex; >>> >>> static void cond_task(void *cookie) >>> { >>> int err; >>> >>> printf("%s --> started \n", __func__); >>> rt_mutex_acquire(&mutex, TM_INFINITE); >>> err = rt_cond_wait(&cond, &mutex, TM_INFINITE); >>> rt_mutex_release(&mutex); >>> if (err) { >>> printf("rt_cond_wait failed, err = %d", err); >>> return; >>> } >>> printf("%s --> cond wait done\n", __func__); >>> } >>> >>> int main(int argc, char **argv) >>> { >>> int err; >>> RT_TASK task1; >>> >>> mlockall(MCL_CURRENT | MCL_FUTURE); >>> >>> err = rt_mutex_create(&mutex, NULL); >>> err = rt_cond_create(&cond, "cond_test"); >>> err = rt_task_create(&task1, NULL, 0, 99, T_JOINABLE); >>> err = rt_task_start(&task1, &cond_task, NULL); >>> rt_mutex_acquire(&mutex, TM_INFINITE); >>> err = rt_cond_signal(&cond); >>> rt_mutex_release(&mutex); >>> if (err) { >>> printf("Error: rt_cond_signal failed, err = %d", err); >>> exit(-1); >>> } >>> printf("%s --> cond signal success: %d\n", __func__, err); >>> printf("Waiting for task to finish....\n"); >>> rt_task_join(&task1); >>> >>> return 0; >>> } >>> ----------------------------------------------------- >>> >>> Is there any fix available in Xenomai-3 for this? >>> Please let me know if there is something wrong here. >>> >>> >> >> You are not using condition variables the right way, those have no >> semaphore semantics. Please read a POSIX documentation about them like >> [1], the alchemy API does not differ in behavior. >> > > Thank you for your reply. > Can you point out the mistake in this program?
No, you need to figure this out by yourself, reading a proper documentation about using POSIX synchronization features. I know, I'm mean. > I will try to develop the posix equivalent and check. > I even tried removing mutex from rt_cond_signal, but it did not help. > No, removing what makes condvars working properly is definitely not going to help. Please grab a POSIX documentation somewhere on the net, a couple of illustrations and use cases, then get your feet wet with mutexes and condition variables: those are the fundamental features POSIX provides for thread synchronization. There is no escape. -- Philippe. _______________________________________________ Xenomai mailing list [email protected] https://xenomai.org/mailman/listinfo/xenomai
