[pthread] Multi pthread

Code

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

#define NUM_THREADS 5

void *thread_function(void *arg);

int main() {
    int res;
    pthread_t a_thread[NUM_THREADS];
    void *thread_result;
    int lots_of_threads;

    for(lots_of_threads = 0; lots_of_threads < NUM_THREADS; lots_of_threads++) {

        res = pthread_create(&(a_thread[lots_of_threads]), NULL, thread_function, (void *)&lots_of_threads);
        if (res != 0) {
            perror("Thread creation failed");
            exit(EXIT_FAILURE);
        }
        sleep(1);
    }

/* Recycle each of pthread */    
    printf("Waiting for threads to finish...\n");
    for(lots_of_threads = NUM_THREADS - 1; lots_of_threads >= 0; lots_of_threads--) {
        res = pthread_join(a_thread[lots_of_threads], &thread_result);
        if (res == 0) {
            printf("Picked up a thread\n");
        }
        else {
            perror("pthread_join failed");
        }
    }
    printf("All done\n");
    exit(EXIT_SUCCESS);
}

void *thread_function(void *arg) {
    int my_number = *(int *)arg;
    int rand_num;

    printf("thread_function is running. Argument was %d\n", my_number);
    rand_num=1+(int)(9.0*rand()/(RAND_MAX+1.0));
    sleep(rand_num);
    printf("Bye from %d\n", my_number);
    pthread_exit(NULL);
}

Result

thread_function is running. Argument was 0
thread_function is running. Argument was 1
thread_function is running. Argument was 2
thread_function is running. Argument was 3
thread_function is running. Argument was 4
Bye from 1
Waiting for threads to finish...
Bye from 0
Bye from 2
Bye from 3
Bye from 4
Picked up a thread
Picked up a thread
Picked up a thread
Picked up a thread
Picked up a thread
All done

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[Pthread][mutex] Pthread + mutex to create synchronize

mutex (programming) 1

Code

#include<stdio.h>
#include<string.h>
#include<pthread.h>
#include<stdlib.h>
#include<unistd.h>
pthread_t tid[2];
int counter;
pthread_mutex_t lock;
void* doSomeThing(void *arg)
{
    pthread_mutex_lock(&lock);

    unsigned long i = 0;
    counter += 1;
    printf("\n Job %d started\n", counter);

    for(i=0; i<(0xFFFFFFFF);i++);

    printf("\n Job %d finished\n", counter);

    pthread_mutex_unlock(&lock);

    return NULL;
}
int main(void)
{
    int i = 0;
    int err;

    if (pthread_mutex_init(&lock, NULL) != 0)
    {
        printf("\n mutex init failed\n");
        return 1;
    }
/* Create two pthread */
    while(i < 2)
    {
        err = pthread_create(&(tid[i]), NULL, &doSomeThing, NULL);
        if (err != 0)
            printf("\ncan't create thread :[%s]", strerror(err));
        i++;
    }
/* pthread 0 go doSomeThing first, then pthread 1 */
    pthread_join(tid[0], NULL);
    pthread_join(tid[1], NULL);
    pthread_mutex_destroy(&lock);

    return 0;
}

Result

 Job 1 started
 Job 1 finished
 Job 2 started
 Job 2 finished

Reference

1. How to Use C Mutex Lock Examples for Linux Thread Synchronization ↩

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[Pthread][Semaphore] Pthread + semaphore to create synchronize

Semaphore (programming) 1

C code

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

void *thread_function(void *arg);
sem_t bin_sem;

#define WORK_SIZE 1024
char work_area[WORK_SIZE];

int main() {
    int res;
    pthread_t a_thread;
    void *thread_result;

/* Initial Semaphore 0 */
    res = sem_init(&bin_sem, 0, 0);
    if (res != 0) {
        perror("Semaphore initialization failed");
        exit(EXIT_FAILURE);
    }
    res = pthread_create(&a_thread, NULL, thread_function, NULL);
    if (res != 0) {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }

    printf("Input some text. Enter 'end' to finish\n");
    while(strncmp("end", work_area, 3) != 0) {
        fgets(work_area, WORK_SIZE, stdin);
        sem_post(&bin_sem); /* Increase Semaphore to 1 ( 0 + 1 ) */
    }
    printf("\nWaiting for thread to finish...\n");
    res = pthread_join(a_thread, &thread_result);
    if (res != 0) {
        perror("Thread join failed");
        exit(EXIT_FAILURE);
    }
    printf("Thread joined\n");
    sem_destroy(&bin_sem);
    exit(EXIT_SUCCESS);
}

void *thread_function(void *arg) {
    sem_wait(&bin_sem); /* decrease Semaphore to 0 ( 1 - 1 ) */
    while(strncmp("end", work_area, 3) != 0) {
        printf("You input %d characters\n", strlen(work_area) -1);
        sem_wait(&bin_sem);  /* wait for another Semaphore, because the value is 0 now */
    }
    pthread_exit(NULL);
}

Result

Input some text. Enter 'end' to finish
This is my first pthread and semaphore.
You input 39 characters
end

Waiting for thread to finish...
Thread joined

Reference

---

1. Semaphore (programming) ↩

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[Pthread] Simple Pthread synchronize

The following code can download from [Linux Programer] 1

C code

/** 
 * 
 * Simple Pthread synchronize
 * 
 */
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
void *thread_function(void *arg);
int run_now = 1;
char message[] = "Hello World";
int main() {
    int res;
    pthread_t a_thread;
    void *thread_result;
    int print_count1 = 0;
/* Start to create pthread */
    res = pthread_create(&a_thread, NULL, thread_function, (void *)message);
    if (res != 0) {
        perror("Thread creation failed");
        exit(EXIT_FAILURE);
    }
/* one pthread go here */
    while(print_count1++ < 20) {
        if (run_now == 1) {
            printf("1");
            run_now = 2; /* When run_now set to 2, then wait for another pthread to execute */
        }
        else {
            sleep(1);
        }
    }
/* Finish pthread */
    printf("\nWaiting for thread to finish...\n");
    res = pthread_join(a_thread, &thread_result);
    if (res != 0) {
        perror("Thread join failed");
        exit(EXIT_FAILURE);
    }
    printf("Thread joined\n");
    exit(EXIT_SUCCESS);
}
void *thread_function(void *arg) {
    int print_count2 = 0;

    while(print_count2++ < 20) {
        if (run_now == 2) {
            printf("2");
            run_now = 1;
        }
        else {
            sleep(1);
        }
    }

    sleep(3);
}

Result

We can understand pthread execute one by one. This synchronize code take too much time.

12121212121212
Waiting for thread to finish...
Thread joined

Reference

---

1. Beginning Linux Programming, 3rd Edition. ↩

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