Karch, Joshua wrote:
> Hi All,
>
> I tried implementing inter-task message queues and following the
> msg_queue.c example
> (http://www.xenomai.org/documentation/trunk/html/api/msg__queue_8c-example.html)
> and when I try to run the implementation after fixing some of the code
> (declaring fail() to printf an error, declaring int err, and changing
> &task_body to &consumer), I get the following error
> msg_queue[3897]: segfault at 00000000 eip b7cf8933 esp bf8dce04 error
> 6. This comes out of the rt_queue_alloc function.
>
> Has the implementation of message passing between userspace tasks
> changed? Is there a more recent example? My end goal is to send non
> blocking messages from one producer task at 50Hz to two reading tasks
> tasks with similar (though not exactly same) loop rates-- i.e. None of
> the tasks are synchronized, though they all run at about 50Hz. Should I
> use message queues to do this?
>
Btw, that code skeleton was meant to be paired with a peer module in
kernel/userland that would create the queue. Nothing in this code does this; you
need to call rt_queue_create() at init to create the queue the consumer task
will bind to.
> Thank you,
>
> Joshua Karch
>
> Attached is the code I used..
>
> #include <sys/mman.h>
> #include <stdio.h>
> #include <string.h>
> #include <native/task.h>
> #include <native/queue.h>
>
> #define TASK_PRIO 99 /* Highest RT priority */
> #define TASK_MODE 0 /* No flags */
> #define TASK_STKSZ 0 /* Stack size (use default one) */
>
> RT_QUEUE q_desc;
>
> RT_TASK task_desc;
>
> void fail()
> {
> printf("error\n");
> }
>
>
> void consumer (void *cookie)
>
> {
> ssize_t len;
> void *msg;
> int err;
>
> /* Bind to a queue which has been created elsewhere, either in
> kernel or user-space. The call will block us until such queue
> is created with the expected name. The queue should have been
> created with the Q_SHARED mode set, which is implicit when
> creation takes place in user-space. */
>
> err = rt_queue_bind(&q_desc,"SomeQueueName",TM_INFINITE);
>
> if (err)
> fail();
>
> /* Collect each message sent to the queue by the queuer() routine,
> until the queue is eventually removed from the system by a call
> to rt_queue_delete(). */
>
> while ((len = rt_queue_receive(&q_desc,&msg,TM_INFINITE)) > 0)
> {
> printf("received message> len=%d bytes, ptr=%p, s=%s\n",
> len,msg,(const char *)msg);
> rt_queue_free(&q_desc,msg);
> }
>
> /* We need to unbind explicitly from the queue in order to
> properly release the underlying memory mapping. Exiting the
> process unbinds all mappings automatically. */
>
> rt_queue_unbind(&q_desc);
>
> if (len != -EIDRM)
> /* We received some unexpected error notification. */
> fail();
>
> /* ... */
> }
>
>
> int main (int argc, char *argv[])
>
> {
> static char *messages[] = { "hello", "world", NULL };
> int n, len;
> void *msg;
> int err;
>
> mlockall(MCL_CURRENT|MCL_FUTURE);
>
> err = rt_task_create(&task_desc,
> "MyTaskName",
> TASK_STKSZ,
> TASK_PRIO,
> TASK_MODE);
> if (!err)
> rt_task_start(&task_desc,&consumer,NULL);
>
> /* ... */
>
> for (n = 0; messages[n] != NULL; n++)
> {
> len = strlen(messages[n]) + 1;
> /* Get a message block of the right size. */
> msg = rt_queue_alloc(&q_desc,len);
>
> if (!msg)
> /* No memory available. */
> fail();
>
> strcpy((char *)msg,messages[n]);
> rt_queue_send(&q_desc,msg,len,Q_NORMAL);
> }
>
> rt_task_delete(&task_desc);
> }
>
>
> ------------------------------------------------------------------------
>
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--
Philippe.
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