解释 pthread_create(&(pool->threads[i]), NULL, thread_func, (void *)pool);

pthread_create() 是一个函数，用于在 POSIX 环境下创建一个新的线程。它的原型如下：

int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);

其中，参数 thread 是指向线程标识符的指针；参数 attr 是指向线程属性的指针；start_routine 是线程启动时要执行的函数；参数 arg 是传递给 start_routine 函数的参数。

调用 pthread_create() 函数后，它将创建一个新的线程，并将线程 ID 存储在 thread 指向的位置。线程将从 start_routine 函数开始执行，并使用 arg 指向的参数。如果成功创建线程，pthread_create() 将返回 0，否则返回一个非零的错误代码。

相关问题

pthread线程池实现快速排序并计时 c++

好的，这是一个比较复杂的问题，需要分步骤来回答。

首先，我们需要实现一个基本的快速排序算法，可以用以下的代码实现：

void quick_sort(int *arr, int left, int right){
    int i, j, pivot, temp;

    if(left < right){
        i = left;
        j = right;
        pivot = arr[left];

        while(i < j){
            while(i < j && arr[j] >= pivot)
                j--;
            if(i < j)
                arr[i++] = arr[j];

            while(i < j && arr[i] < pivot)
                i++;
            if(i < j)
                arr[j--] = arr[i];
        }

        arr[i] = pivot;
        quick_sort(arr, left, i - 1);
        quick_sort(arr, i + 1, right);
    }
}

接下来，我们需要实现一个线程池。这里我们使用pthread库实现。以下是线程池的代码：

typedef struct{
    int *arr;
    int left;
    int right;
} Task;

typedef struct{
    Task *task_queue;
    int queue_head;
    int queue_tail;
    int queue_size;
    pthread_mutex_t queue_lock;
    pthread_cond_t queue_not_empty;
    pthread_cond_t queue_not_full;
    pthread_t *threads;
    int thread_count;
    int is_shutdown;
} ThreadPool;

void thread_pool_init(ThreadPool *pool, int thread_count, int queue_size){
    pool->thread_count = thread_count;
    pool->queue_size = queue_size;
    pool->queue_head = pool->queue_tail = 0;
    pool->is_shutdown = 0;
    pool->threads = (pthread_t *)malloc(sizeof(pthread_t) * thread_count);
    pool->task_queue = (Task *)malloc(sizeof(Task) * queue_size);

    pthread_mutex_init(&(pool->queue_lock), NULL);
    pthread_cond_init(&(pool->queue_not_empty), NULL);
    pthread_cond_init(&(pool->queue_not_full), NULL);

    for(int i = 0; i < thread_count; i++)
        pthread_create(&(pool->threads[i]), NULL, thread_func, (void *)pool);
}

void thread_pool_add_task(ThreadPool *pool, Task task){
    pthread_mutex_lock(&(pool->queue_lock));
    while((pool->queue_tail + 1) % pool->queue_size == pool->queue_head){
        pthread_cond_wait(&(pool->queue_not_full), &(pool->queue_lock));
    }

    pool->task_queue[pool->queue_tail] = task;
    pool->queue_tail = (pool->queue_tail + 1) % pool->queue_size;

    pthread_cond_signal(&(pool->queue_not_empty));
    pthread_mutex_unlock(&(pool->queue_lock));
}

void thread_pool_shutdown(ThreadPool *pool){
    pthread_mutex_lock(&(pool->queue_lock));
    pool->is_shutdown = 1;
    pthread_cond_broadcast(&(pool->queue_not_empty));
    pthread_mutex_unlock(&(pool->queue_lock));

    for(int i = 0; i < pool->thread_count; i++)
        pthread_join(pool->threads[i], NULL);

    free(pool->threads);
    free(pool->task_queue);

    pthread_mutex_destroy(&(pool->queue_lock));
    pthread_cond_destroy(&(pool->queue_not_empty));
    pthread_cond_destroy(&(pool->queue_not_full));
}

void *thread_func(void *arg){
    ThreadPool *pool = (ThreadPool *)arg;
    Task task;

    while(1){
        pthread_mutex_lock(&(pool->queue_lock));
        while(pool->queue_head == pool->queue_tail && !pool->is_shutdown){
            pthread_cond_wait(&(pool->queue_not_empty), &(pool->queue_lock));
        }

        if(pool->is_shutdown){
            pthread_mutex_unlock(&(pool->queue_lock));
            pthread_exit(NULL);
        }

        task = pool->task_queue[pool->queue_head];
        pool->queue_head = (pool->queue_head + 1) % pool->queue_size;

        pthread_cond_signal(&(pool->queue_not_full));
        pthread_mutex_unlock(&(pool->queue_lock));

        quick_sort(task.arr, task.left, task.right);
    }
}

最后，我们需要实现计时功能。可以用以下代码实现：

#include <sys/time.h>

double get_time(){
    struct timeval tv;
    gettimeofday(&tv, NULL);
    return tv.tv_sec + tv.tv_usec / 1000000.0;
}

现在我们需要将这些代码组合起来，实现一个快速排序的线程池，并计时。以下是完整的代码：

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <sys/time.h>

typedef struct{
    int *arr;
    int left;
    int right;
} Task;

typedef struct{
    Task *task_queue;
    int queue_head;
    int queue_tail;
    int queue_size;
    pthread_mutex_t queue_lock;
    pthread_cond_t queue_not_empty;
    pthread_cond_t queue_not_full;
    pthread_t *threads;
    int thread_count;
    int is_shutdown;
} ThreadPool;

void quick_sort(int *arr, int left, int right){
    int i, j, pivot, temp;

    if(left < right){
        i = left;
        j = right;
        pivot = arr[left];

        while(i < j){
            while(i < j && arr[j] >= pivot)
                j--;
            if(i < j)
                arr[i++] = arr[j];

            while(i < j && arr[i] < pivot)
                i++;
            if(i < j)
                arr[j--] = arr[i];
        }

        arr[i] = pivot;
        quick_sort(arr, left, i - 1);
        quick_sort(arr, i + 1, right);
    }
}

void thread_pool_init(ThreadPool *pool, int thread_count, int queue_size){
    pool->thread_count = thread_count;
    pool->queue_size = queue_size;
    pool->queue_head = pool->queue_tail = 0;
    pool->is_shutdown = 0;
    pool->threads = (pthread_t *)malloc(sizeof(pthread_t) * thread_count);
    pool->task_queue = (Task *)malloc(sizeof(Task) * queue_size);

    pthread_mutex_init(&(pool->queue_lock), NULL);
    pthread_cond_init(&(pool->queue_not_empty), NULL);
    pthread_cond_init(&(pool->queue_not_full), NULL);

    for(int i = 0; i < thread_count; i++)
        pthread_create(&(pool->threads[i]), NULL, thread_func, (void *)pool);
}

void thread_pool_add_task(ThreadPool *pool, Task task){
    pthread_mutex_lock(&(pool->queue_lock));
    while((pool->queue_tail + 1) % pool->queue_size == pool->queue_head){
        pthread_cond_wait(&(pool->queue_not_full), &(pool->queue_lock));
    }

    pool->task_queue[pool->queue_tail] = task;
    pool->queue_tail = (pool->queue_tail + 1) % pool->queue_size;

    pthread_cond_signal(&(pool->queue_not_empty));
    pthread_mutex_unlock(&(pool->queue_lock));
}

void thread_pool_shutdown(ThreadPool *pool){
    pthread_mutex_lock(&(pool->queue_lock));
    pool->is_shutdown = 1;
    pthread_cond_broadcast(&(pool->queue_not_empty));
    pthread_mutex_unlock(&(pool->queue_lock));

    for(int i = 0; i < pool->thread_count; i++)
        pthread_join(pool->threads[i], NULL);

    free(pool->threads);
    free(pool->task_queue);

    pthread_mutex_destroy(&(pool->queue_lock));
    pthread_cond_destroy(&(pool->queue_not_empty));
    pthread_cond_destroy(&(pool->queue_not_full));
}

void *thread_func(void *arg){
    ThreadPool *pool = (ThreadPool *)arg;
    Task task;

    while(1){
        pthread_mutex_lock(&(pool->queue_lock));
        while(pool->queue_head == pool->queue_tail && !pool->is_shutdown){
            pthread_cond_wait(&(pool->queue_not_empty), &(pool->queue_lock));
        }

        if(pool->is_shutdown){
            pthread_mutex_unlock(&(pool->queue_lock));
            pthread_exit(NULL);
        }

        task = pool->task_queue[pool->queue_head];
        pool->queue_head = (pool->queue_head + 1) % pool->queue_size;

        pthread_cond_signal(&(pool->queue_not_full));
        pthread_mutex_unlock(&(pool->queue_lock));

        quick_sort(task.arr, task.left, task.right);
    }
}

double get_time(){
    struct timeval tv;
    gettimeofday(&tv, NULL);
    return tv.tv_sec + tv.tv_usec / 1000000.0;
}

int main(){
    int arr[1000000];

    for(int i = 0; i < 1000000; i++)
        arr[i] = rand() % 1000000;

    ThreadPool pool;
    thread_pool_init(&pool, 4, 10000);

    double start_time = get_time();

    Task task;
    task.arr = arr;
    task.left = 0;
    task.right = 999999;
    thread_pool_add_task(&pool, task);

    thread_pool_shutdown(&pool);

    double end_time = get_time();

    printf("Time: %lf\n", end_time - start_time);

    return 0;
}

运行程序，可以看到输出的时间，就是快速排序的时间。注意，线程池的线程数和任务队列大小可以根据自己的需求进行调整。

线程池计算素数：编写一个程序primer_thr3.c，程序运行开始时，创建10个子线程和一个包含20个元素的队列，主线程不断地依次将30000000到30000200之间这200个数放入队列，如果队列满，则主线程等待。

以下是完整的primer_thr3.c程序代码，实现了线程池计算素数的功能：

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

#define QUEUE_SIZE 20
#define THREAD_COUNT 10

typedef struct {
    int num;
    int is_prime;
} task_t;

int start = 30000000;
int end = 30000200;
int *results;
pthread_mutex_t result_lock = PTHREAD_MUTEX_INITIALIZER;

typedef struct {
    task_t *tasks;
    int capacity;
    int front;
    int rear;
    pthread_mutex_t lock;
    pthread_cond_t not_empty;
    pthread_cond_t not_full;
    pthread_t *threads;
    int thread_count;
    int stop;
} thread_pool_t;

void init_thread_pool(thread_pool_t *pool, int capacity, int thread_count);
void *thread_func(void *arg);
int is_prime(int num);

int main() {
    results = malloc((end - start + 1) * sizeof(int));
    thread_pool_t pool;
    init_thread_pool(&pool, QUEUE_SIZE, THREAD_COUNT);
    for (int i = start; i <= end; i++) {
        task_t task = {i, 0};
        pthread_mutex_lock(&pool.lock);
        while ((pool.rear + 1) % pool.capacity == pool.front) {
            pthread_cond_wait(&pool.not_full, &pool.lock);
        }
        pool.tasks[pool.rear] = task;
        pool.rear = (pool.rear + 1) % pool.capacity;
        pthread_cond_signal(&pool.not_empty);
        pthread_mutex_unlock(&pool.lock);
    }
    while (1) {
        pthread_mutex_lock(&pool.lock);
        if (pool.front == pool.rear) {
            pthread_mutex_unlock(&pool.lock);
            break;
        }
        pthread_mutex_unlock(&pool.lock);
    }
    pool.stop = 1;
    pthread_cond_broadcast(&pool.not_empty);
    for (int i = 0; i < pool.thread_count; i++) {
        pthread_join(pool.threads[i], NULL);
    }
    pthread_mutex_destroy(&pool.lock);
    pthread_cond_destroy(&pool.not_empty);
    pthread_cond_destroy(&pool.not_full);
    free(pool.tasks);
    free(pool.threads);
    for (int i = start; i <= end; i++) {
        printf("%d %s\n", i, results[i - start] ? "is prime" : "is not prime");
    }
    free(results);
    return 0;
}

void init_thread_pool(thread_pool_t *pool, int capacity, int thread_count) {
    pool->tasks = malloc(capacity * sizeof(task_t));
    pool->capacity = capacity;
    pool->front = 0;
    pool->rear = 0;
    pthread_mutex_init(&pool->lock, NULL);
    pthread_cond_init(&pool->not_empty, NULL);
    pthread_cond_init(&pool->not_full, NULL);
    pool->threads = malloc(thread_count * sizeof(pthread_t));
    pool->thread_count = thread_count;
    pool->stop = 0;
    for (int i = 0; i < thread_count; i++) {
        pthread_create(&pool->threads[i], NULL, thread_func, pool);
    }
}

void *thread_func(void *arg) {
    thread_pool_t *pool = (thread_pool_t *) arg;
    while (1) {
        pthread_mutex_lock(&pool->lock);
        while (pool->front == pool->rear && !pool->stop) {
            pthread_cond_wait(&pool->not_empty, &pool->lock);
        }
        if (pool->stop) {
            pthread_mutex_unlock(&pool->lock);
            pthread_exit(NULL);
        }
        task_t task = pool->tasks[pool->front];
        pool->front = (pool->front + 1) % pool->capacity;
        pthread_cond_signal(&pool->not_full);
        pthread_mutex_unlock(&pool->lock);
        task.is_prime = is_prime(task.num);
        pthread_mutex_lock(&result_lock);
        results[task.num - start] = task.is_prime;
        pthread_mutex_unlock(&result_lock);
    }
    return NULL;
}

int is_prime(int num) {
    if (num < 2) {
        return 0;
    }
    for (int i = 2; i * i <= num; i++) {
        if (num % i == 0) {
            return 0;
        }
    }
    return 1;
}

程序首先定义了一个任务结构体task_t，其中包含一个待计算的数值num和一个标志位is_prime，表示该数值是否为素数。然后定义了一个线程池结构体thread_pool_t，包含一个任务队列和一定数量的线程。线程池的初始化函数init_thread_pool中包括创建任务队列、初始化线程和启动线程等步骤。

主函数main中循环向任务队列中添加任务，并通过线程池的线程函数thread_func计算素数并回传计算结果。最后等待所有任务完成后销毁线程池，并通过results数组输出计算结果。

线程函数thread_func中取出任务、计算素数和回传结果等步骤，其中使用了互斥锁和条件变量保证了线程安全。计算素数的函数is_prime使用了较为简单的算法判断是否为素数。