[并发并行]_[线程模型]_[Pthread线程使用模型之三 客户端/服务端模型(Client/Server]

Pthread线程使用模型之三 客户端/服务端模型(Client/Server)

场景

1.在客户端/服务端模型时,客户端向服务端请求一些数据集的操作. 服务端执行执行操作独立的(多进程或跨网络)– 客户端可以等待服务端响应再做其他任务或者做一些并行的操作,在一段时间后被通知时再去查询结果. 虽然客户端等待服务端是最简单的方式, 但是这种情况极少使用, 因为它不具备速度和性能优势, 同步的只适合获取一些普通的资源. 比如Socket i/O的非阻塞或异步模型.

2.在做一些复杂的命令行程序时(单元测试),也需要这种模型.比如实现并发的方法测试,或者需要异步网络通讯的测试,或者通按键的功能执行(1: 执行导入. 2: 执行输出 q:执行退出)

说明

1. Server的作用就是并发的处理请求并分发任务.
2. Client可以同步等待或者异步执行, 在实际的项目开发中, 一般是Socket i/o来实现 Client和Server.

例子

1.程序server.c, 每个线程都在反复的读,接着输出, 输入几行. 当程序在运行时, 你能看到线程在不同的顺序输出提醒, 也有其他线程在输出之前先提示. 但是你将不会发现一个提示或一个输出在prompt服务器里穿插在提示和读取(stdin)之间.

2.request_t结构体定义了对服务器的每个请求. 未处理的requests使用next来连接成链表.

3.tty_server_t结构体提供server线程的上下文.它有两个同步对象(mutex and request). 一个标记位表明了这个服务是否正在运行, 同时一个requests列表表明了有哪些未处理的请求.

4.主程序和客户端线程使用同步对象client_mutex和clients_done来通讯, 而不是使用pthread_join.

5.创建detach线程的两种方法:

// 方法1:
pthread_t thread;
pthread_attr_t detached_attr;

status = pthread_attr_init (&detached_attr);
if (status != 0)
    err_abort (status, "Init attributes object");
status = pthread_attr_setdetachstate (
    &detached_attr, PTHREAD_CREATE_DETACHED);
if (status != 0)
    err_abort (status, "Set detach state");
tty_server.running = 1;
status = pthread_create (&thread, &detached_attr,
    tty_server_routine, NULL);

// 方法2:
pthread_t thread;
status = pthread_create (&thread, NULL,
    tty_server_routine, NULL);
pthread_detach(thread);

/*
 * server.c
 *
 * Demonstrate a client/server threading model.
 *
 * Special notes: On a Solaris system, call thr_setconcurrency()
 * to allow interleaved thread execution, since threads are not
 * timesliced.
 */
#include <pthread.h>
#include <math.h>
#include "errors.h"

#define CLIENT_THREADS  4               /* Number of clients */

#define REQ_READ        1               /* Read with prompt */
#define REQ_WRITE       2               /* Write */
#define REQ_QUIT        3               /* Quit server */

/*
 * Internal to server "package" -- one for each request.
 */
typedef struct request_tag {
    struct request_tag  *next;          /* Link to next */
    int                 operation;      /* Function code */
    int                 synchronous;    /* Non-zero if synchronous */
    int                 done_flag;      /* Predicate for wait */
    pthread_cond_t      done;           /* Wait for completion */
    char                prompt[32];     /* Prompt string for reads */
    char                text[128];      /* Read/write text */
} request_t;

/*
 * Static context for the server
 */
typedef struct tty_server_tag {
    request_t           *first;
    request_t           *last;
    int                 running;
    pthread_mutex_t     mutex;
    pthread_cond_t      request;
} tty_server_t;

tty_server_t tty_server = {
    NULL, NULL, 0,
    PTHREAD_MUTEX_INITIALIZER, PTHREAD_COND_INITIALIZER};

/*
 * Main program data
 */

int client_threads;
pthread_mutex_t client_mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t clients_done = PTHREAD_COND_INITIALIZER;

/*
 * The server start routine. It waits for a request to appear
 * in tty_server.requests using the request condition variable.
 * It processes requests in FIFO order. If a request is marked
 * "synchronous" (synchronous != 0), the server will set done_flag
 * and signal the request's condition variable. The client is
 * responsible for freeing the request. If the request was not
 * synchronous, the server will free the request on completion.
 */
void *tty_server_routine (void *arg)
{
    static pthread_mutex_t prompt_mutex = PTHREAD_MUTEX_INITIALIZER;
    request_t *request;
    int operation, len;
    int status;

    while (1) {
        status = pthread_mutex_lock (&tty_server.mutex);
        if (status != 0)
            err_abort (status, "Lock server mutex");

        /*
         * Wait for data
         */
        while (tty_server.first == NULL) {
            status = pthread_cond_wait (
                &tty_server.request, &tty_server.mutex);
            if (status != 0)
                err_abort (status, "Wait for request");
        }
        request = tty_server.first;
        tty_server.first = request->next;
        if (tty_server.first == NULL)
            tty_server.last = NULL;
        status = pthread_mutex_unlock (&tty_server.mutex);
        if (status != 0)
            err_abort (status, "Unlock server mutex");

        /*
         * Process the data
         */
        operation = request->operation;
        switch (operation) {
            case REQ_QUIT:
                break;
            case REQ_READ:
                if (strlen (request->prompt) > 0)
                    printf (request->prompt);
                if (fgets (request->text, 128, stdin) == NULL)
                    request->text[0] = '\0';
                /*
                 * Because fgets returns the newline, and we don't want it,
                 * we look for it, and turn it into a null (truncating the
                 * input) if found. It should be the last character, if it is
                 * there.
                 */
                len = strlen (request->text);
                if (len > 0 && request->text[len-1] == '\n')
                    request->text[len-1] = '\0';
                break;
            case REQ_WRITE:
                puts (request->text);
                break;
            default:
                break;
        }
        if (request->synchronous) {
            status = pthread_mutex_lock (&tty_server.mutex);
            if (status != 0)
                err_abort (status, "Lock server mutex");
            request->done_flag = 1;
            status = pthread_cond_signal (&request->done);
            if (status != 0)
                err_abort (status, "Signal server condition");
            status = pthread_mutex_unlock (&tty_server.mutex);
            if (status != 0)
                err_abort (status, "Unlock server mutex");
        } else
            free (request);
        if (operation == REQ_QUIT)
            break;
    }
    return NULL;
}

5.tty_server_routine用来持续处理客户端请求直到退出请求发出. 如果一个请求标记为同步(synchronous不为0),那么server设置done_flag的值并且通知done条件变量. 当请求是同步的, 那么客户端有责任去释放request包. 如果请求是异步的, 那么server在完成request时会释放.

void tty_server_request (
    int         operation,
    int         sync,
    const char  *prompt,
    char        *string)
{
    request_t *request;
    int status;

    status = pthread_mutex_lock (&tty_server.mutex);
    if (status != 0)
        err_abort (status, "Lock server mutex");
    if (!tty_server.running) {
        pthread_t thread;
        pthread_attr_t detached_attr;

        status = pthread_attr_init (&detached_attr);
        if (status != 0)
            err_abort (status, "Init attributes object");
        status = pthread_attr_setdetachstate (
            &detached_attr, PTHREAD_CREATE_DETACHED);
        if (status != 0)
            err_abort (status, "Set detach state");
        tty_server.running = 1;
        status = pthread_create (&thread, &detached_attr,
            tty_server_routine, NULL);
        if (status != 0)
            err_abort (status, "Create server");

        /*
         * Ignore an error in destroying the attributes object.
         * It's unlikely to fail, there's nothing useful we can
         * do about it, and it's not worth aborting the program
         * over it.
         */
        pthread_attr_destroy (&detached_attr);
    }

    /*
     * Create and initialize a request structure.
     */
    request = (request_t*)malloc (sizeof (request_t));
    if (request == NULL)
        errno_abort ("Allocate request");
    request->next = NULL;
    request->operation = operation;
    request->synchronous = sync;
    if (sync) {
        request->done_flag = 0;
        status = pthread_cond_init (&request->done, NULL);
        if (status != 0)
            err_abort (status, "Init request condition");
    }
    if (prompt != NULL)
        strncpy (request->prompt, prompt, 32);
    else
        request->prompt[0] = '\0';
    if (operation == REQ_WRITE && string != NULL)
        strncpy (request->text, string, 128);
    else
        request->text[0] = '\0';

    /*
     * Add the request to the queue, maintaining the first and
     * last pointers.
     */
    if (tty_server.first == NULL) {
        tty_server.first = request;
        tty_server.last = request;
    } else {
        (tty_server.last)->next = request;
        tty_server.last = request;
    }

    /*
     * Tell the server that a request is available.
     */
    status = pthread_cond_signal (&tty_server.request);
    if (status != 0)
        err_abort (status, "Wake server");

    /*
     * If the request was "synchronous", then wait for a reply.
     */
    if (sync) {
        while (!request->done_flag) {
            status = pthread_cond_wait (
                &request->done, &tty_server.mutex);
            if (status != 0)
                err_abort (status, "Wait for sync request");
        }
        if (operation == REQ_READ) {
            if (strlen (request->text) > 0)
                strcpy (string, request->text);
            else
                string[0] = '\0';
        }
        status = pthread_cond_destroy (&request->done);
        if (status != 0)
            err_abort (status, "Destroy request condition");
        free (request);
    }
    status = pthread_mutex_unlock (&tty_server.mutex);
    if (status != 0)
        err_abort (status, "Unlock mutex");
}

6.tty_server_request 用来初始化一个发送到tty server的请求. 如果tty server线程没有在运行, 启动一个, 并创建一个属性对象(detached_attr)， 并设置detachstate属性值为 PTHREAD_CREATE_DETACHED.

PTHREAD_CREATE_JOINABLE – pthread_create创建时默认就是joinable, 意味着通过pthread_create创建的线程id能被用来join with这个线程,查询线程的返回值或者取消它.

PTHREAD_CREATE_DETACHED – 通过pthread_create创建的id是不能再用饿了,当线程终止时, 任何被线程使用的资源都会被系统迅速回收. 也可以在pthread_create之后通过pthread_detach转换为detach线程. 建议如果不需要控制线程, 就把它设置为detach.

7.分配和初始化一个server的请求(request_t)包. 如果请求是同步的, 初始化request里的条件变量done(注意配合使用的还是server的mutex,这里和server共用mutex,如果是同步请求的话,server只能等待client的请求完成并释放mutex才能继续执行下一个request,效率并不高)

/*
 * Client routine -- multiple copies will request server.
 */
void *client_routine (void *arg)
{
    int my_number = (int)arg, loops;
    char prompt[32];
    char string[128], formatted[128];
    int status;

    sprintf (prompt, "Client %d> ", my_number);
    while (1) {
        tty_server_request (REQ_READ, 1, prompt, string);
        if (strlen (string) == 0)
            break;
        for (loops = 0; loops < 4; loops++) {
            sprintf (
                formatted, "(%d#%d) %s", my_number, loops, string);
            tty_server_request (REQ_WRITE, 0, NULL, formatted);
            sleep (1);
        }
    }
    status = pthread_mutex_lock (&client_mutex);
    if (status != 0)
        err_abort (status, "Lock client mutex");
    client_threads--;
    if (client_threads <= 0) {
        status = pthread_cond_signal (&clients_done);
        if (status != 0)
            err_abort (status, "Signal clients done");
    }
    status = pthread_mutex_unlock (&client_mutex);
    if (status != 0)
        err_abort (status, "Unlock client mutex");
    return NULL;
}

int main (int argc, char *argv[])
{
    pthread_t thread;
    int count;
    int status;

#ifdef sun
    /*
     * On Solaris 2.5, threads are not timesliced. To ensure
     * that our threads can run concurrently, we need to
     * increase the concurrency level to CLIENT_THREADS.
     */
    DPRINTF (("Setting concurrency level to %d\n", CLIENT_THREADS));
    thr_setconcurrency (CLIENT_THREADS);
#endif

    /*
     * Create CLIENT_THREADS clients.
     */
    client_threads = CLIENT_THREADS;
    for (count = 0; count < client_threads; count++) {
        status = pthread_create (&thread, NULL,
            client_routine, (void*)count);
        if (status != 0)
            err_abort (status, "Create client thread");
    }
    status = pthread_mutex_lock (&client_mutex);
    if (status != 0)
        err_abort (status, "Lock client mutex");
    while (client_threads > 0) {
        status = pthread_cond_wait (&clients_done, &client_mutex);
        if (status != 0)
            err_abort (status, "Wait for clients to finish");
    }
    status = pthread_mutex_unlock (&client_mutex);
    if (status != 0)
        err_abort (status, "Unlock client mutex");
    printf ("All clients done\n");
    tty_server_request (REQ_QUIT, 1, NULL, NULL);
    return 0;
}