一个进程池的服务器程序

下面做了非常简单的http服务器，该服务器只能接收Get请求。
流程大概如下：
1，父进程listen，创建pipe（下面所有父子进程之间的通信都用该pipe）
2，父进程预fork n个子进程
3，各个子进程accept(listenfd)，即所有子进程竞争accept请求。由于listenfd是在fork之前就有的，所以所有子进程都可以访问到，不需用到“进程间文件描述符传递”问题；
4，子进程每accept到一个请求都告诉父进程，父进程把请求数加1；子进程没完成一个请求，父进程把请求数减1；当父进程发现请求数 >= 子进程数时，父进程创建新的子进程，并把子进程数加1（当然子进程数有个预先上限）；当父进程发现子进程数大于请求数加1时，父进程杀死多余的子进程。
总的来说，思想是让子进程accept并处理请求，父进程通过子进程发来的信息控制请求数与子进程数之间的关系。

代码如下：
代码如下：

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define PRECHILD    5
#define MAXCHILD    50
#define BUFSIZE 4096
#define PIDPATH    "pid"
#define head503    "HTTP/1.1 503 Service unavailable\r\n"
#define head404 "HTTP/1.1 404 Not Found\r\n"
#define head200 "HTTP/1.1 200 0K\n\rContent—Type: text/html\n\rContent—Length: "

int len503, len404, len200;
int fd1[2], fd2[2];

typedef struct {
    pid_t pid;
    char status; // 'n' means new request; 'f' means finish the request
} REPORT;

void answer(int listenfd)
{
    int connfd;
    char buf[BUFSIZE];
    int count;
    int pid = getpid();
    struct     sockaddr_in cliaddr;
    int size = sizeof(cliaddr);
    
    char comm;
    REPORT rep;
    rep.pid = pid;
    while (1) {
        connfd = accept(listenfd, (struct sockaddr *)&cliaddr,(socklen_t *)&size );    //子进程accept请求
        rep.status = 'n';
        if (write(fd1[1], &rep, sizeof(rep)) < 0) { //通知父进程已经accept了请求
            perror("write pipe new failed");
            exit(-1);
        }

    count = read(connfd, buf, BUFSIZE);
    char req[10];
    char filepath[256];
    
    sscanf(buf, "%s%s", req, filepath + 1);
    filepath[0] = '.';
    if (strcmp("GET", req) != 0) {//503
        write(connfd, head503, len503);
        //goto err_out;
        close(connfd);
        exit(-1);
    }
    char content[BUFSIZE];
    struct stat stbuf;
    if (lstat(filepath, &stbuf) != 0) {
        int err = errno;
        if (err == ENOENT) {//404
            write(connfd, head404, len404);        
        }
        close(connfd);
        exit(-1);
    }
    count = write(connfd, head200, len200);
    u_int filesize = stbuf.st_size;
    sprintf(content, "%u\n\r\n\r", filesize);
    count = write(connfd, content, strlen(content));
    FILE *fp = fopen(filepath, "r");
    if (fp == NULL) {
        printf("open file %s failed\n", filepath);
        close(connfd);
        exit(-1);
    }
    while((count = fread(content, 1, sizeof(content), fp)) > 0) {
        //printf("%s", content);
        if (write(connfd, content, count) != count) {
                printf("write failed\n");
        }
    }
    fclose(fp);
        close(connfd);
        
        rep.status = 'f';
        if (write(fd1[1], &rep, sizeof(rep)) < 0) {//告诉父进程自己处理完了请求
            perror("write pipe finish failed");
            exit(-1);
        }
        
        if (read(fd2[0], &comm, 1) < 1) {//等待来自父进程的命令
            perror("read pipe failed");
            exit(-1);
        }
        //printf("[%d] reve %c from pa\n", pid, comm);
        if (comm == 'e') { //收到exit命令
            printf("[%d] exit\n", pid);
            exit(-1);
        }
        else if (comm == 'c') { //收到继续accept的命令
            printf("[%d] continue\n", pid);
        }
        else {
            printf("[%d] comm : %c illeagle\n", pid, comm);
        }
    }
}

void usage()
{
    printf("Usage: http-serv port\n");
}

int write_pid()
{
    int fd;
    if ((fd = open(PIDPATH, O_WRONLY | O_TRUNC | O_CREAT, S_IWUSR)) < 0){
        perror("open pidfile faild");
        return -1;
    }
    struct flock lock;
    lock.l_type = F_WRLCK;
    lock.l_start = 0;
    lock.l_whence = SEEK_SET;
    lock.l_len = 0;
    
    if (fcntl(fd, F_SETLK, &lock) == -1) {
        int err = errno;
        perror("fcntl faild");
        if (err == EAGAIN) {
            printf("Another http-serv process is running now!\n");
        }
        return -1;
    }    
    return 0;
}

void daemon_init()
{
    //clear file creation mask;
    umask(0);
    
    //become a session leader
    if (fork() != 0)
        exit(-1);
    if (setsid() < 0)
        exit(-1);
    
    //make sure can be never get the TTY control
    if (fork() != 0)
        exit(-1);
        
    //may chdir here
    
    int i;
    for (i = 0; i < 1024; i++)
        close(i);

     /*
     * Attach file descriptors 0, 1, and 2 to /dev/null.
     */
    int fd0, fd1, fd2;
  fd0 = open("/dev/null", O_RDWR);
  fd1 = dup(0);
  fd2 = dup(0);
    if (fd0 != 0 || fd1 != 1 || fd2 != 2) {
        printf("init failed\n");
        exit(-1);
    }

}

int
main(int argc, char **argv)
{
    int     listenfd;
  struct     sockaddr_in servaddr;
    pid_t pid;
    
    if (argc != 2) {
        usage();
        return -1;
    }
    
    signal(SIGCHLD, SIG_IGN);
 
    len200 = strlen(head200);
    len404 = strlen(head404);
    len503 = strlen(head503);
    
    daemon_init();    //转为后台程序，如需打印调试，把这行注释掉
    if (write_pid() < 0) //避免同时有多个该程序在运行
        return -1;  
    if (pipe(fd1) < 0) {
        perror("pipe failed");
        exit(-1);
    }
    if (s_pipe(fd2) < 0) {
        perror("pipe failed");
        exit(-1);
    }    
    int port = atoi(argv[1]);        
    //initialize servaddr and listenfd...
  bzero(&servaddr, sizeof(servaddr));
  servaddr.sin_family = AF_INET;
  servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  servaddr.sin_port = htons(port);
    
  listenfd = socket(AF_INET, SOCK_STREAM, 0);
  bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr));
  listen(listenfd, 1000);
    int i;
    for (i = 0; i < PRECHILD ; i++) { //父进程预fork 子进程
        if ((pid = fork()) < 0) {
            perror("fork faild");
            exit(3);
        }
        else if (pid == 0) {
            answer(listenfd);
        }
        else {
            printf("have create child %d\n", pid);
        }        
    }
                
    char e = 'e';
    char c = 'c';
    int req_num = 0;
    int child_num = PRECHILD;
    REPORT rep;
    while (1) {
        //printf("req_num = %d, child_num = %d\n", req_num, child_num);
        if (read(fd1[0], &rep, sizeof(rep)) < sizeof(rep)) {//等待子进程发来消息
            perror("parent read pipe failed");
            exit(-1);
        }
        //printf("parent: receive from %d\n", pid);
        if (rep.status == 'n') {//子进程刚accept了新的请求
            req_num ++;
            printf("parent: %d have receive new request\n", rep.pid);       
            if (req_num >= child_num && child_num <= MAXCHILD) { //请求数过多，创建更多子进程
                if ((pid = fork()) < 0) {
                    perror("fork faild");
                    exit(3);
                }
                else if (pid == 0) {
                    answer(listenfd);
                }
                else {
                    printf("have create child %d\n", pid);
                    child_num ++;
                }        
            }
        }
        else if (rep.status == 'f') {//子进程刚处理完了一个请求
            req_num --;
            //printf("parent: %d have finish a request\n", rep.pid);            
            if (child_num > (req_num + 1) && child_num > PRECHILD) {//子进程数过多，删除多余的子进程
                if (write(fd2[1], &e, sizeof(e)) < sizeof(e)) {
                    perror("pa write pipe failed");
                    exit(-2);
                }
                //printf("tell child exit\n");
                child_num --;
            }
            else {
                if (write(fd2[1], &c, sizeof(c)) < sizeof(c)) {//让子进程继续等待accept
                    perror("pa write pipe failed");
                    exit(-2);
                }
                //printf("tell child continue\n");
            }            
        }
    }    
    return 0;
}