signals

I'm working on a program which uses shared memory. Multiple instances of said program will either connect to an existing one or create it anew, and give it back to OS when there are no other processes or just detach it and terminate. I thought of using a simple counter to keep track of how many processes use it. I'm using atexit() function to do the cleanup, however, afaik, upon receiving SIGKILL signal, processes won't do any cleanup, so if any of those processes don't terminate normally, I might never be able to clean the memory. Is there a way to specify what to do even after a SIGKILL

I am attaching a method to the post_save signal of my Django model. This way I can clear some cached items whenever the model is modified. The problem I am having is that the signal is being triggered twice when the model is saved. It doesn't necessarily hurt anything (the code will just gracefully error out) but it can't be right. A quick example, just printing the model to the console (using the dev server): from blog.models import Post from django.db.models import signals def purge_cache(sender, **kwargs): print 'Purging %s' % sender signals.post_save.connect(purge_cache, sender=Post) This

In C, I can say #include <stdio.h> #include <unistd.h> #include <signal.h> int continue_running = 1; void handler(int signal, siginfo_t* info, void* data) { printf("got signal %d from process %d running as user %d\n", signal, info->si_pid, info->si_uid); continue_running = 0; } int main(int argc, char** argv) { struct sigaction sa; sigset_t mask; sigemptyset(&mask); sa.sa_sigaction = &handler; sa.sa_mask = mask; sa.sa_flags = SA_SIGINFO; sigaction(SIGTERM, &sa, NULL); printf("pid is %d\n", getpid()); while (continue_running) { sleep(1); }; return 0; } This prints out something like pid is

did anyone who knows how to use the sigaltstack in a real signal handler program,a simple but complete code may be great help to me! thank you in advance! Here is a minimal sample program that uses sigaltstack to catch infinite recursion. If you comment out the sigaltstack call or SA_ONSTACK flag, the signal handler will not be able to run because it has no stack left and the program will just crash. #define _XOPEN_SOURCE 700 #include <signal.h> #include <unistd.h> void handler(int sig) { write(2, "stack overflow\n", 15); _exit(1); } unsigned infinite_recursion(unsigned x) { return infinite

I am examining a few crashes that all have the signal SIGSEGV with the reason SEGV_ACCERR. After searching for SEGV_ACCERR, the closest thing I have found to a human readable explanation is: Invalid Permissions for object What does this mean in a more general sense? When would a SEGV_ACCERR arise? Is there more specific documentation on this reason? This is an error that I have mostly seen on 64 bit iOS devices and can happen if multiple threads read and change a variable under ARC. For example, I fixed a crash today where multiple background threads were reading and using a static NSDate and

I have this code which listens to USR1 signals import signal import os import time def receive_signal(signum, stack): print 'Received:', signum signal.signal(signal.SIGUSR1, receive_signal) signal.signal(signal.SIGUSR2, receive_signal) print 'My PID is:', os.getpid() while True: print 'Waiting...' time.sleep(3) This works when I send signals with kill -USR1 pid But how can I send the same signal from within the above python script so that after 10 seconds it automatically sends USR1 and also receives it , without me having to open two terminals to check it? moomima You can use os.kill() : os