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Re: Scheduler problem
- From: Nick Garnett <nickg at ecoscentric dot com>
- To: "liu hua" <rongye_liu at hotmail dot com>
- Cc: ecos-discuss at sources dot redhat dot com
- Date: 04 Apr 2005 16:53:32 +0100
- Subject: Re: [ECOS] Scheduler problem
- References: <BAY12-F145477A494A48C0D006527E8380@phx.gbl>
"liu hua" <rongye_liu@hotmail.com> writes:
> In the tewothreads example program, if I don't use cyg_thread_delay()
> in the 'simple_program' thread, or if use cyg_thread_delay(0), the two
> threads cannt be scheduled normally. The result is only one thread
> can run, and another thread is hung. thread program:
> void simple_program(cyg_addrword_t data)
> {
> int message = (int) data;
> int delay;
>
> printf("Beginning execution; thread data is %d\n", message);
>
> //cyg_thread_delay(200);
>
> for (;;) {
> //delay = 0+ (rand() % 0);
>
> /* note: printf() must be protected by a
> call to cyg_mutex_lock() */
> cyg_mutex_lock(&cliblock); {
> printf("Thread %d: and now a delay of %d clock ticks\n",
> message, delay);
> }
> cyg_mutex_unlock(&cliblock);
> cyg_thread_delay(0);
> }
> }
> Output result:
> Thread 0: and now a delay of 0 clock ticks
> Thread 0: and now a delay of 0 clock ticks
> Thread 0: and now a delay of 0 clock ticks
> Thread 0: and now a delay of 0 clock ticks
> ...
Thread 0 is higher priority that thread 1. Without the delays, thread
0 is always runnable and will always occupy the CPU. Thread 1 will
never get to execute.
>
> So, in my ecos application which have many thread have follow program:
> while (1)
> {
> ...
> }
If you write all your threads to just loop like this, then only the
highest priority thread will run. Just like you discovered above.
> If must I use cyg_thread_delay(delay) in it? ie:
> while (1)
> {
> ...
> cyg_thread_delay(delay);
> }
>
> If I must use cyg_thread_delay() in these threads, the performance of
> ecos will be a bad thing.
The general approach for writing multi-threaded applications is to
make threads wait for some event, do some processing, and then go back
to waiting. The event may be an interrupt, a timer, or a
synchronization action by some other thread.
--
Nick Garnett eCos Kernel Architect
http://www.ecoscentric.com The eCos and RedBoot experts
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