RE: can linux RT thread corrupt global variable?

I am not an expert on this.
As a test try using a mutex to protect cpl from thread switching during
modification.

//somewhere on top of your program.
static pthread_mutex_t mtxThread = PTHREAD_MUTEX_INITIALIZER;
....
...
//in you threads.
pthread_mutex_lock(&mtxThread); 
cpl=1234 //however you are modifying it.
pthread_mutex_unlock(&mtxThread);
......


On Monday, May 05, 2003 8:40 PM, Ming Lei [SMTP:[email protected]] wrote:
> Platform:
> Intel Pentium II; RedHat 7.2 with kernel version 2.4.7-10, libc 2.2.4-13
and
> gcc 2.96.
> 
> Problem description:
> 
> a program has a thread of priority 12, a thread of priority 10, a thread
of
> priority 6, and the main process at priority 0. All the threads except
main
> process is created with pthread_create, and defined SCHED_FIFO as real
time
> scheduler policy.
> 
> There is a global variable I define as 'int cpl'. All the threads and main
> process may alter cpl at any time. cpl may have one of these values {0,
> 0xf000006e, 0xf0000068, 0xe0000000, 0xe0000060}.
> 
> <Problem=> at some point of execution which cpl should be a value say
> e0000060, but the actual value retained at cpl is another say e0000000;
that
> is, the value is changed without the program actually done anything on it.
> The retained value I observed is kind of historic value(one of these value
> in the above set), not the arbituary value. The problem had occured just
> after context switch, also occured during a thread execution.
> 
> <Confirm> I used Intel debug register to track any writing to the cpl
memory
> address globally, which is the way GDB use for x86 hardware watchpoint
> implementation. I could see all the writing from my program to change cpl,
> but failed to see the source from which the problem occured. So I dont
know
> what cause the problem.
> 
> Can anyone listening give me a direction or hint on this annoying
situation?
> Any help is thanked here.
> 
> PS. please cc to this email address.
> -Ming
> 
> 
> Related questions:
> 
> Is linux kernel 2.4.10 considered strictly preemptive such as VxWorks or
> other RTOS? I guess 2.4.10 may simulate preemptive with running scheduler
on
> every syscall or interrupt returns. Am I right?
> 
> Is printf() real-time priority thread safe?
> 
> 
> 
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