signals

Work in Progress

Summary

POSIX signals

Signal	Meaning	Default Action
`SIGINT`	interrupt from keyboard (ctrl+c)	terminate
`SIGTERM`	termination request	terminate
`SIGKILL`	immediate kill	terminate (cannot be caught)
`SIGSTOP`	stop process	stop (cannot be caught)
`SIGCONT`	continue stopped process	continue
`SIGALRM`	timer expired	terminate
`SIGCHLD`	child process state change	ignore by default
`SIGSEGV`	illegal memory access (seg fault)	terminate, dump core

POSIX syscalls for signals

Syscall	Include	Function
`kill(pid, sig)`	`<signal.h>`	sends a signal to a process or process group
`signal(sig, handler)`	`<signal.h>`	installs a simple signal handler for a signal
`raise(sig)`	`<signal.h>`	sends a signal to the calling/current process
`pause()`	`<unistd.h>`	suspends the process until a signal is received
`alarm(time)`	`<unistd.h>`	schedules a `SIGALRM` signal after a specified number of seconds

Concept

asynchronous notification regarding an event
a software interrupt sent to a process
handling:
- default handler
- user supplied handler
sent by:
- another process
- OS
- the same process

#include <stdio.h>
#include <signal.h>
#include <unistd.h>

void myOwnHandler(int signo) {
	if (signo == SIGSEGV){
		printf("Memory access blows up!\n");
		exit(1);     
	}
}

int main() {
	int *ip = NULL;
	if (signal(SIGSEGV, myOwnHandler) == SIG_ERR) // replace the default handler
		printf("Failed to register handler\n");
	
	*ip = 123; // causes seg fault
	
	return 0;
}