Interrupts on threads

[philipsan]

I want to know how I can make interrupts on threads.

Example:
1 thread is using 2 ressources of the same kind. Then comes a second thread which needs to use 1 of the same kind of ressources..

How can I interrupt the first thread, so that the second thread can get the ressource needed?

much thanks

[philipsan]

by the way, it's linux programming with c

[philipsan]

I just need to know where I can read about my problem. I dont request anybody to actually write code.

[Ancient Dragon]

look for "semiphores", which synchronizes the use of objects between threads. When the program starts it creates a semaphone. Then when one thread needs access to an object it first requests access to the semaphone from the operating system. If no other threads are using the semaphore the os grants access, otherwise if another thread is using the semaphone the os blocks the thread until either a timeout expires or the semaphone is released by the other thread.

[philipsan]

I made made this following code:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>

#include "patientStruct.h"

#define LOGFILE		"logFil.txt"

sem_t dame1;
skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade)


int main(int argc, char *argv[])
{
	sem_init(&dame1,0,1);
	int i;
	

	while(i=0; i < Patient[MAX]; i++) //sålænge et eller andet mht. patienterne..
	{
		printf("Patient %d bliver nu modtaget af dame1\n", i, 0);

		//Kritisk område start
		sem_wait(&dame1);

			printf("Dame1 har skrevet Patient %d i log'en\n", i);
			skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade) // Here I want to write         to logfil.txt
			
			sleep(Random(2)+2);

		sem_post(&dame1);
		//Kritisk område slut
		
	}
}

/*
	Skriver tekst til logFil.txt, samt til skærm
*/
void skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade)
{
	FILE *fp = fopen(LOGFILE, "a");
	fprintf(fp, p[MAX].cprnr, p[MAX].prio, p.[MAX].skade);
	fclose(fp);
}

But I need 2 processes, who constantly take threads, who are in a queue, and write their nformation to logfil.txt.
How do I make 2 processes, who communicate with a queue of threads, with the above semaphore?

[philipsan]

each thread is a patient, for whom the variables cprnr, prio and skade are defined in patientStruct.h

[fgw_three]

Unless I'm missing something, and to be honest I don't work with threads much, but you are not creating any threads.

You just seem to have a single process that loops around, using semaphores to wait and post.

You've include pthread.h, but you're not calling pthread_create or anything like that.

Perhaps something like this might help: pthread tutorial

Good luck.....

[philipsan]

Yeah, I dont create any threads, because they are created elsewhere. This code, should just let each thread enter, write to logifl.txt and then leave, allowing the next thread to do the same

[fgw_three]

Yeah, I dont create any threads, because they are created elsewhere. This code, should just let each thread enter, write to logifl.txt and then leave, allowing the next thread to do the same

Okay, my bad.....

[philipsan]

I made this code now:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include <sys/types.h>

#include "patientStruct.h"

#define LOGFILE		"logFil.txt"

sem_t dame1;
skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade)


int main(int argc, char *argv[])
{
	sem_init(&dame1,0,1);
	int i, n;
	pid_t pid;
	
	pid = fork();
	
	switch(pid)
	{
	case -1:
		perror("fork failed!");
		exit(1);
	case 0:
	
		while(i=0; i < Patient[MAX]; i++) //sålænge et eller andet mht. patienterne..
		{
		printf("Patient %d bliver nu modtaget af dame1\n", i, 0);
		
		//Kritisk område start
		sem_wait(&dame1);

			printf("Dame1 har skrevet Patient %d i log'en\n", i);
			skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade)
			
			sleep(2);

		sem_post(&dame1);
		//Kritisk område slut
		}
	default:
		while(i=0; i < Patient[MAX]; i++) //sålænge et eller andet mht. patienterne..
		{
		printf("Patient %d bliver nu modtaget af dame1\n", i, 0);
		
		//Kritisk område start
		sem_wait(&dame1);

			printf("Dame1 har skrevet Patient %d i log'en\n", i);
			skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade)
			
			sleep(2);

		sem_post(&dame1);
		//Kritisk område slut
		}
		break;
	}
	exit(0);	
}

/*
	Skriver tekst til logFil.txt, samt til skærm
*/
void skrivTilLog(p[MAX].cprnr, p[MAX].prio, p.[MAX].skade)
{
	FILE *fp = fopen(LOGFILE, "a");
	fprintf(fp, p[MAX].cprnr, p[MAX].prio, p.[MAX].skade);
	fclose(fp);
}

I need this code to go through all the patients(threads) via their information, which lies in my struct.

Is this somewhat more correct?
thanks all