[SOLVED] How to implement a function that the program can pause at any time and continue

mirage1993 · 04-19-2014, 10:48 PM

I want to write a program .its function very simple.
when I run it ,it will display some numbers. when I take some action such as press 's',it will pause until I press 'g'.
in short,I want to implement a function that the program can pause at any time,and continue.
I tried to use semaphore,but I failed.

reference the original code:

Code:

#include<stdio.h>
#include<unistd.h>
#include<string.h>
#include<stdlib.h>
#include<pthread.h>
#include<semaphore.h>
void *thread_function(void *arg);
int worksize=10;
//char workarea[worksize];
char workarea[10];
sem_t sem;//critical
sem_t full;
sem_t empty;
int in=0,out=0;
int main()
{
    int res;
    FILE *fp;
    int ch;
    pthread_t a_thread;
    void *thread_result;
/////////semaphore init////////
    res=sem_init(&sem,0,1);
    if(res!=0)
        {perror("error:");exit(1);}
    res=sem_init(&full,0,0);
    if(res!=0)
        {perror("error:");exit(1);}
    res=sem_init(&empty,0,worksize);
    if(res!=0)
        {perror("error:");exit(1);}
/////////creat thread///////////
    res=pthread_create(&a_thread,NULL,thread_function,NULL);
    if(res!=0)
        {perror("error:");exit(1);}
/////////open file/////////////
    if((fp=fopen("/home/mirage/Desktop/program/pie.txt","r"))==NULL)
        {perror("error:");exit(1);}
///////////producer-read from file////////////
    while(1)
    {
        sem_wait(&empty);
        sem_wait(&sem);     //critical section
            if((ch=fgetc(fp))==EOF)
                break;
            workarea[in]=ch;
            in=(in+1)%worksize;//
        sem_post(&sem);    //no critical section
        sem_post(&full);
    }//while
    sem_destroy(&sem);
    sem_destroy(&empty);
    sem_destroy(&full);
    fclose(fp);
    exit(0);
}//main
///////////consumer-output to terminal////////////
void *thread_function(void *arg)
{
    int ent=0;
    printf("pie=:3.\n");
    while(1)
    {
        sem_wait(&full);
        sem_wait(&sem);     //critical section
            usleep(80000);
            printf("%c",workarea[out]);
            fflush(stdout);
            ent++;
            if(ent==10)
                {printf("\n");ent=0;}
            out=(out+1)%worksize;
        sem_post(&sem);     //no critical section
        sem_post(&empty);
    }//while
}

mina86 · 04-20-2014, 05:30 AM

Instead of semaphores, use POSIX conditional variables:

Code:

pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t condvar = PTHREAD_COND_INITIALIZER;
bool paused = false;

void thread1() {
	for (;;) {
		sleep(10);

		pthread_mutex_lock(&mutex);
		paused = !paused;
		if (!paused) {
			pthread_cond_broadcast(&cond);
		}
		pthread_mutex_unlock(&mutex);
	}
}

void thread2() {
	for (;;) {
		pthread_mutex_lock(&mutex);
		while (paused) {
			pthread_cond_wait(&cond, &mutex);
		}
		pthread_mutex_unlock(&mutex);

		puts(".");
		sleep(1);
	}
}

(Not tested, not compiled).