Hi guys,
this is my first posting, so at first hi to everyone!
I have a problem with ucontext_t in connection with signal handling. I want to simulate a preemptive scheduler. I am using the iTimer with ITIMER_PROF, to schedule the interrupts. You find the code below:
The "thread function" includes two big for-loops and print-outs, whether the loops finished successfully or not. Unfortunately it doesn't work fine at all runs. Sometimes the for- loops stop before reaching the end condition (i < UPPER_BOUND). This seems to depend from the UPPER_BOUND variable and the length of interval (QUANTUM_SEC and QUANTUM_MICRO_SEC). My first idea was, that the context saving does not save the value of i. But this can't be the reason, because often the loops "survive" the first signals. Because it's hard to debug this signal and context switching stuff, I've decided to ask you. I hope you have more knowledge about what's going on inside the OS. I didn't find much stuff at the web concerning this concrete topic. So, thank your for your help and let me know if you need further information.
I am using a Ubuntu 8.04 in a VMWare Player.
Best,
Matthias
Last edited by XComp; 11-24-2008 at 05:05 PM..
Reason: adding descriptions to the functions in the code
Sure, if you think that there is a better chance for an answer. At first I thought that this is more low-level programming. But anyway...can you move it to the High Level Programming Subforum?!
Ok...I've tried to reduce the code. Maybe it is easier to understand and nobody is scared by the big number of lines. I removed most of the if conditions. So let's take a second try!
Interesting problem. What happens when you run your program natively? VMware has some gotchas that can trip you up when you try doing what you are trying to do.
So I've tested it on a OpenSuse machine. And there it behaves a little bit different. Instead of finishing there will be raised a segmentation fault. Here is the sample output for UPPER_BOUND = 500000000 and 500 ms intveral:
Ubuntu and VMWare:
What could be the reason of this segmentation fault. Could it be raised because of some mistakes in initializing the alternative signal stack? Does anyone has a good source, which explains, what happens inside the OS, when a context is swapped or a signal is raised? I didn't find anything on the web... :/
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