Messages in this thread | | | From | "Perez-Gonzalez, Inaky" <> | Subject | RE: can linux RT thread corrupt global variable? | Date | Thu, 8 May 2003 13:46:27 -0700 |
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> From: Ming Lei [mailto:lei.ming@attbi.com] > > ... > > 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.
Probably GCC is keeping the value of the variable around in some register. Did you declare the global variable as 'volatile'? [as in "it can be modified by entities external to the flow of the code"]. Try that.
On the other hand - being an integer, access should be atomic, most of the time, but I would not really trust that, at least portability wise. Protecting access to it with a mutex would be a good idea ...
> Is linux kernel 2.4.10 considered strictly preemptive such as VxWorks or > other RTOS?
Nope
> I guess 2.4.10 may simulate preemptive with running scheduler on > every syscall or interrupt returns. Am I right?
You need the preemption patches or 2.5
I hope you are not trying to do serious real-time w/ Linux ... are you?
> Is printf() real-time priority thread safe?
Dunno - you'd have to check the internal implementation in glibc. Last time I heard anything about it, it had some mutex dangling around, but I could be wrong.
Iñaky Pérez-González -- Not speaking for Intel -- all opinions are my own (and my fault) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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