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Pass user parameter to signal handler in linux

This is a discussion on Pass user parameter to signal handler in linux within the Linux Programming forums, part of the Platform Specific Boards category; Hi In my program, I want to use signal handler so that if signal alarm is sent to the process ...

  1. #1
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    Pass user parameter to signal handler in linux

    Hi
    In my program, I want to use signal handler so that if signal alarm is sent to the process my function is to called.till no everything is ok.but I want to pass some parameters to signal handler.but "signal" function does not have any parameter for this. according to it's prototype:
    Code:
    sighandler_t signal (int signum, sighandler_t action)

    Thanks for any help or guidance

  2. #2
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    there's also sigaction, but it also doesn't allow a user-defined pointer to be sent to the handler. there may be a way to do it, but as far as I know, signal and sigaction are the only way to get signals in linux.

  3. #3
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    Unfortunately there is no way to pass user data to the signal handler. This is actually one of the few cases where global variables are an acceptable solution.

  4. #4
    Captain Crash brewbuck's Avatar
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    A signal handler is a global object in every sense. If you need to "pass" data into it, it must be done with a global variable.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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    Hi
    Thanks for your reply.
    I did not want to use Global Variable at all.But I think there is no any way.
    Maybe it's better that I study more on limitation and disadvantage of global variables.I always think that use of Global Variable is bad idea in program.

    Thanks in advance

  6. #6
    spurious conceit MK27's Avatar
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    You can put the signal handler in a file by itself like this:

    Code:
    static void *Data;
    
    void initializeData (void *p) { 
    	Data = p; 
    }
    
    void handler (int sig) {
    	// access *Data here
    }
    Then you call initializeData() before you register the handler with signal(). Since *Data is declared static, only handler() has access to it.

    However, if you are adverse to globals, you might also want to think about how a signal handler is itself "a global object in every sense" even if it doesn't access any data, implying it has a restricted use value. What signal do you want to catch and why?
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

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    In our program I have used timer for some purpose. I have used "create_time" with signal alarm,after timer expiration, one signal alarm is sent to my process.
    So I have to handle signal in my program.

    Thanks again

  8. #8
    spurious conceit MK27's Avatar
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    What's the purpose of the timer? If the signal handler initiates a sequence where you are writing to anything used elsewhere, or reading data that the process might have been writing to at the time, I would think this is subject to the same caveats as threading, namely, that even with a single int, it is possible that you occasionally interrupt a write halfway through (meaning, reading from that int will produce a garbage value), in which case you would be better off actually using a thread and proper thread safe locks on the data.

    Code:
    #include <stdio.h>
    #include <pthread.h>
    #include <unistd.h>
    
    // compile C99 -lpthread
    
    // for passing data to the timer
    struct threadData {
    	pthread_mutex_t *lock;
    	int sleepTime;
    	int *data;
    };
    
    // timer function
    void *timer (void *data) {
    	struct threadData *td = data;
    
    	sleep(td->sleepTime);
    
    	pthread_mutex_lock(td->lock);
    	// reset
    	*(td->data) = 0;
    	pthread_mutex_unlock(td->lock);
    
    	return NULL;
    }
    
    int main(void) {
    	pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
    	int x = 1;
    	struct threadData data = {
    		.lock = &lock,
    		.sleepTime = 3,
    		.data = &x
    	};
    	pthread_t id;
    
    // create and detach the timer
    	pthread_create(&id, NULL, timer, (void*)&data);
    	pthread_detach(id);
    	
    // do stuff until the timer goes off
    	while (1) {
    		pthread_mutex_lock(&lock);
    		if (!x) break;
    		printf("%d\n", x++);
    		pthread_mutex_unlock(&lock);
    	}
    
    	printf("done\n");
    
    	pthread_mutex_destroy(&lock);
    
    	return 0;
    }
    Last edited by MK27; 04-03-2012 at 07:58 AM.
    phantomotap likes this.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  9. #9
    Master Apprentice phantomotap's Avatar
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    The only way I know to do this portably would see you using a thread to watch a variable triggered by the signal anyway; you should just use "Posix" facilities from the outset.

    Soma

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