Linux多线程-信号量

#include <iostream>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>

int g_val = 100;

pthread_mutex_t mutex;
sem_t sem;
pthread_mutex_t c_mutex;

void* sonThreadFunc(void* param)
{
    usleep(1000);
    std::cout << pthread_self() << " " << *(int *)param << std::endl;
    sem_post(&sem);

    usleep(1000);
    pthread_mutex_lock(&mutex);

    ++g_val;

    std::cout << pthread_self() << " " << g_val << std::endl;
    pthread_mutex_unlock(&mutex);
    return NULL;
}

int main()
{
    pthread_mutex_init(&mutex, NULL);
    pthread_mutex_init(&c_mutex, NULL);
    sem_init(&sem, 0, 0);
    pthread_t tid[20];
    for(size_t i = 0; i < 20; i++)
    {
        if(pthread_create(&tid[i], NULL, sonThreadFunc, &i) != 0)
        {
            break;
        }
        sem_wait(&sem);
    }
    for(size_t i = 0; i < 20; i++)
    {
        pthread_join(tid[i], NULL);
    }
    pthread_mutex_destroy(&mutex);
    pthread_mutex_destroy(&c_mutex);
    sem_destroy(&sem);
    std::cout << "Hello World!" << std::endl;
    return 0;
}