c语言进程池的简单实现

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一、背景

上期文章提了一下线程池的简单实现,本期顺势也把进程池的学习过程给大家分享一下吧;

二、相关知识

2.1 进程池的使用场景

进程池与线程池出发点一样,都是考虑多核情况下任务的并行处理;
从多进程和多线程编程的区别上看,多线程有许多的同步、互斥的方法,较擅长于异步协作;而多进程同步、互斥的方法相对比较麻烦,则更多地考虑上下文独立执行;
从Nginx使用线程池/进程池处理大并发的思路去分析,其实就是多客户端大量连接的场景;主进程监听是否有新客户端tcp连接,然后分发给工作进程去响应http请求,在这种场景下每个连接都是一个独立的上下文逻辑,每个工作进程的内容都是对等地处理http请求,这种情况就非常适合进程池的方式;

2.2 进程池的工作流程

把上述的场景给抽象出来,关注于父子进程的通讯,也就是下图流程:

Master主进程给Worker子进程分发任务,通讯的方式用的就是单向管道的方式;
分发任务这块,可以有随机分发、轮流分发、计分板等多种方法,具体可以结合业务进行设计;

三、实现原型

本节根据上述流程图进行一个简单的实现,假设分别有A、B、C三种任务,主进程使用轮流分发(Round-robin)把任务均匀地分配给子进程们;
在结构体process上得考虑一下,Master进程需要保存所有子进程的进程号、管道号;
/* Process struct */typedef struct process{        char name[SIZE_NAME_NORMAL];                    /* Process name */        pid_t pid;                                      /* Process id */        int pipefd[2];                                  /* Connection between master/slave */        size_t score;                                   /* Score record */} process_t;/* Program instance */typedef struct instance{        char prg_name[SIZE_NAME_LONG];                  /* Program name with path */        char cfg_name[SIZE_NAME_LONG];                  /* Configure name with path */        u16 process_num;                                /* Sub process number */        u16 process_idx;                                /* Current process index */        struct process *proc;                           /* Process struct */} instance_t;

进程池的初始化函数,根据给定的Worker进程数开启子进程;

int process_pool(instance_t *pinst, u16 process_num){    int ret = FAILURE;    int ix  = 0;    int status = 0;    if ( !pinst || !process_num ) {        printf("NULL\n");        goto _E1;    }    signal(SIGINT,  __sig_quit);    signal(SIGTERM, __sig_quit);    pinst->process_idx = 0;    pinst->process_num = process_num;    pinst->proc = (process_t *)calloc(process_num + 1, sizeof(process_t));    if ( !pinst->proc ) {        printf("Alloc process pool struct failed\n");        goto _E1;    }    for ( ix = 1; ix <= process_num; ix++ ) {        int bufsize = 1;        ret = pipe(pinst->proc[ix].pipefd);        if ( SUCCESS != ret ) {            printf("socketpair\n");            goto _E2;        }        printf("Setup worker#%u\n", ix);        pinst->proc[ix].pid = fork();        if ( pinst->proc[ix].pid < 0 ) {            printf("fork\n");            goto _E2;        }        else if ( pinst->proc[ix].pid > 0 ) {            /* Father */            CLOSE_FD(pinst->proc[ix].pipefd[0]);            continue;        }        else {            /* Child */            CLOSE_FD(pinst->proc[ix].pipefd[1]);            pinst->process_idx = ix;            ret = __worker(pinst);            goto _E2;        }    }    ret = __master(pinst);    /* Waiting workers */    for ( ix = 1; ix <= pinst->process_num; ix++ ) {        waitpid(pinst->proc[ix].pid, &status, WNOHANG);    }_E2:    for ( ix = 1; ix <= pinst->process_num; ix++ ) {        CLOSE_FD(pinst->proc[ix].pipefd[1]);        CLOSE_FD(pinst->proc[ix].pipefd[0]);    }    FREE_POINTER(pinst->proc);_E1:    return ret;}

然后就是Master Worker的实现,Master就是简单地进行一个事件分发,通过约定的协议"ABC"代表三种工作命令,“Q“代表退出进程;
static int __master(instance_t *pinst){    int ret  = 0;    int fd   = 0;    int ix   = 0;    int roll = 0;    char c = 0;#define __offset(pinst) ((pinst)->proc[(pinst)->process_idx])#define __round_robin(pinst, roll) \    ((pinst)->proc[((roll) % (pinst)->process_num) + 1].pipefd[1])    printf("Master#%u setup\n", pinst->process_idx);    for ( g_enable = 1; g_enable; ) {        /* Get pipe fd by round-robin */        fd = __round_robin(pinst, ++roll);        c = 'A' + roll % 3; // 'A'/'B'/'C'        ret = write(fd, &c, 1);        if ( ret <= 0 ) {            return FAILURE;        }        sleep(1);    }    /* Tell all workers to quit */    for ( ix = 1; ix <= pinst->process_num; ix++ ) {        c = 'Q';        write(__round_robin(pinst, ++roll), &c, 1);    }    printf("Master#%u shutdown\n", pinst->process_idx);    return SUCCESS;}

static int __worker(instance_t *pinst){    int fd = __offset(pinst).pipefd[0];    int ix = 0;    ssize_t read_byte = FAILURE;    char buffer[1024] = {0};    printf("Worker#%u setup\n", pinst->process_idx);    for ( g_enable = 1; g_enable; ) {        read_byte = read(fd, buffer, sizeof(buffer));        if ( read_byte <= 0 ) {            if ( errno == EAGAIN || errno == EINTR ) {                continue;            }            return FAILURE;        }        for ( ix = 0; ix < read_byte; ix++ ) {            switch ( buffer[ix] ) {                case 'A':                case 'B':                case 'C':                    __offset(pinst).score += buffer[ix];                    printf("Worker#%u Recv command: %c, score: %llu\n",                            pinst->process_idx,                            buffer[ix], __offset(pinst).score);                    break;                case 'Q':                    printf("Quit\n");                    g_enable = 0;                    break;                default:                    break;            }        }    }    printf("Worker#%u shutdown\n", pinst->process_idx);    return SUCCESS;}
最后带一个main方法,考虑了进程释放的问题,在这个demo中使用信号对genable进行控制;
static u8 g_enable;                         /* Running flag */static void __sig_quit(int sig){    g_enable = 0;}int main(int argc, char *argv[]){    instance_t inst = {0};    if ( argc < 2 ) {        printf("Usage: \n\t%s < process number >\n", argv[0]);        return EXIT_FAILURE;    }    return process_pool(&inst, atoi(argv[1]));}

四、总结

在本次demo原型中,进程池的开启方法process_pool()是比较通用的,管道的方法除了pipe也可以用socketpair;
在功能扩展方面,要考虑的还有协议的完善、子进程执行结果是否需要告知主进程、应用socket的I/O复用、完善信号的处理等;


参考文章:
[1] http://blog.csdn.net/al_xin/article/details/39258067
[2] http://blog.csdn.net/u010693037/article/details/51335038
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