HELP: Threads: strange behaiviour (???)

[Joel Sherrill <joel@OARcorp.com>]

Alex wrote:
> Hi, 
> 
> I have a rtems program that launchs 2 extra threads. Each thread shares the same execution function.
> Each thread, main included, uses the SCHED_RR with poriority 1.
> The objective is to run the threads at the same time as possible sharing the time slice. In other words, I 
> want to execute each thread in each quantum, so I choosed the SCHED_RR.
> 
> What I get is the first extra thread running till the end and then the second extra thread begins execution.
> Why both extra threads didn't start execution "at the same time?"
> 
> The output I get is:
> 
> ...
> WAITING FOR SECONDARY THREADS
> 
> secondary thread: beginning
> 
> "some moments after..."
> 
> secondary thread: finishing
> 
> secondary thread: beginning
> 
> "some moments after..."
> 
> secondary thread: finishing
> ...
> 
> 
> 
> The output I expected was:
> 
> ...
> secondary thread: beginning
> secondary thread: beginning
> 
> "some moments after..."
> 
> secondary thread: finishing
> secondary thread: finishing
> ...
> 
> Do you agree with me?

Maybe yes, maybe now. :)

I think your secondary thread could be running to completion in less 
than a timeslice.  Some things to try:

   + Why status += in Task_1?
   + Change the for in Task_1 to something that actually ensures it is
     hanging around for at least 1 or 2 clock ticks.  Watch "current"
     until it changes more than a timeslice.

--joel

> This is source code:
> 
> #define CONFIGURE_INIT
> #include <rtems.h>
> #include <signal.h>
> #include <rtems/posix/timer.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <errno.h>
> #include <rtems/error.h>
> #include <bsp.h>
> #include <pthread.h>
> #ifndef _POSIX_THREADS
> 	#error "rtems is supposed to have pthreads"
> #endif
> 
> #include <assert.h>
> #include <string.h>
> #include <time.h>
> #include <unistd.h>
> #include <time.h>
> #include <sched.h>
> 
> 
> void *Task_1(void *argument)
> {
>   int i=0;
>   int status;
>   struct timespec current;
> 
>   puts("\nSecondary Thread: beginning" );
>   for (i=0;i<100000000;i++)
>   {
>     status += clock_gettime( CLOCK_REALTIME, &current );
>   }
> 
>   puts("\nSecondary Thread: finishing" );
>   pthread_exit( NULL );
>   return NULL;
> }
> 
> 
> #define CONFIGURE_INIT_TASK_ENTRY_POINT   POSIX_Init
> void POSIX_Init(void* args)
> {
>   const int MAX_THREADS 	=10;
>   const int n_number_of_counts 	=10;   
> 
>   int 			i=0;
>   pthread_t        	Task_ids[MAX_THREADS];
>   pthread_t        	Init_id;
>   int              	status;
>   pthread_attr_t   	attr1;
>   pthread_attr_t   	attr2;
>   struct sched_param  	param;
>   
> 
>   puts("\n\nSTARTING THE MAIN PROGRAM");
>   Init_id = pthread_self();
>   param.sched_priority = 1;
>   status = pthread_setschedparam(Init_id, SCHED_RR, &param);
> 
>   puts("\nCREATING THE SECONDARY THREADS");
>   
>   status = pthread_attr_init(&attr1); 
>   if(status!=0)
>   {
>     puts("\n Error in pthread_attr_init1()");
>     exit(1);
>   }
>   attr1.schedpolicy = SCHED_RR;
>   attr1.schedparam.sched_priority = 1;
> 
>   status = pthread_attr_init(&attr2); 
>   if(status!=0)
>   {
>     puts("\n Error in pthread_attr_init1()");
>     exit(1);
>   }
>   attr2.schedpolicy = SCHED_RR;
>   attr2.schedparam.sched_priority = 1;
> 
> 
>   status = pthread_create(&(Task_ids[0]),&attr1,Task_1,NULL);
>   if(status!=0)
>   {
>     puts("\n Error in pthread_create1()");
>     exit(1);
>   }
> 
>   status = pthread_create(&(Task_ids[1]),&attr2,Task_1,NULL);
>   if(status!=0)
>   {
>     puts("\n Error in pthread_create2()");
>     exit(1);
>   }
> 
>   puts("\nAFTER THREADS CREATION...\n"); 
>   
>   puts( "\nWAITING FOR SECONDARY THREADS..." );
>   status = pthread_join( Task_ids[0], NULL );
>   if(status!=0)
>   {
>     puts("\n Error in pthread_join0()");
>     exit(1);
>   }
> 
>   status = pthread_join( Task_ids[1], NULL );
>   if(status!=0)
>   {
>     puts("\n Error in pthread_join1()");
>     exit(1);
>   }
> 
>   puts("\nEND OF PROGRAM ***");
>   exit(1);
> }
> 
> 
> #define CONFIGURE_MICROSECONDS_PER_TICK 1000  /*one milisecond per tick*/
> #define CONFIGURE_TICKS_PER_TIMESLICE   1     /*each time slice runs for one milisecond*/
> #define CONFIGURE_RTEMS_INIT_TASKS_TABLE
> #define CONFIGURE_POSIX_INIT_THREAD_TABLE
> #define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
> #define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
> #define CONFIGURE_MAXIMUM_TASKS             	 20
> #define CONFIGURE_MAXIMUM_POSIX_THREADS     	 20
> #define CONFIGURE_MAXIMUM_SEMAPHORES        	 20
> #define CONFIGURE_MAXIMUM_MESSAGE_QUEUES    	 20
> #define CONFIGURE_MAXIMUM_POSIX_TIMERS 		 20
> #define CONFIGURE_MAXIMUM_TIMERS 		 20
> #define CONFIGURE_MAXIMUM_POSIX_QUEUED_SIGNALS 	 20
> #define CONFIGURE_EXTRA_TASK_STACKS  		 (3 * RTEMS_MINIMUM_STACK_SIZE)
> #include <confdefs.h>
> 
> 
> 
> 
> 
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-- 
Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
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