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:lei.ming@xxxxxxxxx] 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? > > > > _______________________________________________ > Redhat-devel-list mailing list > Redhat-devel-list@xxxxxxxxxx > https://listman.redhat.com/mailman/listinfo/redhat-devel-list _______________________________________________ Redhat-devel-list mailing list Redhat-devel-list@xxxxxxxxxx https://listman.redhat.com/mailman/listinfo/redhat-devel-list