第五种  TCP预先派生子进程服务器程序：

对预先派生子进程服务器的最后一种改动就是由父进程调用accept，然后再将所接受的已连接描述字传递给子进程。父进程必须跟踪子进程的忙闲状态，以便给空闲子进程传递新的描述字。为每个子进程维护一个信息结构，用来管理各子进程。

在调用fork之前，先创建一个字节流管道（Unix域的字节流套接口），它是Unix域的字节流套接口。当子进程派生后，父进程关闭一个描述字（sockfd[1]），子进程关闭另一个描述字（sockfd[0]）,此外，子进程将流管道的字节所在端（sockfd[1]）复制到标准输出。

child.h:

typedef struct {pid_t        child_pid;      /* process ID */int     child_pipefd;   /* parent's stream pipe to/from child */int        child_status;   /* 0 = ready */long        child_count;    /* # connections handled */
} Child;Child   *cptr;      /* array of Child structures; calloc'ed */

Child.c:

/* include child_make */
#include    "unp.h"
#include    "child.h"Child    *cptr;      /* array of Child structures; calloc'ed */
pid_t
child_make(int i, int listenfd, int addrlen)
{int        sockfd[2];pid_t pid;void    child_main(int, int, int);Socketpair(AF_LOCAL, SOCK_STREAM, 0, sockfd);if ( (pid = Fork()) > 0) {Close(sockfd[1]);cptr[i].child_pid = pid;cptr[i].child_pipefd = sockfd[0];cptr[i].child_status = 0;return(pid);     /* parent */}Dup2(sockfd[1], STDERR_FILENO);        /* child's stream pipe to parent */Close(sockfd[0]);Close(sockfd[1]);Close(listenfd);                  /* child does not need this open */child_main(i, listenfd, addrlen);    /* never returns */
}
/* end child_make *//* include child_main */
void
child_main(int i, int listenfd, int addrlen)
{char           c;int               connfd;ssize_t          n;void          web_child(int);printf("child %ld starting\n", (long) getpid());for ( ; ; ) {if ( (n = Read_fd(STDERR_FILENO, &c, 1, &connfd)) == 0)err_quit("read_fd returned 0");if (connfd < 0)err_quit("no descriptor from read_fd");web_child(connfd);              /* process request */Close(connfd);Write(STDERR_FILENO, "", 1);   /* tell parent we're ready again */}
}
/* end child_main */

pr_cpu_time.c:

#include "unp.h"
#include    <sys/resource.h>#ifndef   HAVE_GETRUSAGE_PROTO
int     getrusage(int, struct rusage *);
#endifvoid
pr_cpu_time(void)
{double         user, sys;struct rusage myusage, childusage;if (getrusage(RUSAGE_SELF, &myusage) < 0)err_sys("getrusage error");if (getrusage(RUSAGE_CHILDREN, &childusage) < 0)err_sys("getrusage error");user = (double) myusage.ru_utime.tv_sec +myusage.ru_utime.tv_usec/1000000.0;user += (double) childusage.ru_utime.tv_sec +childusage.ru_utime.tv_usec/1000000.0;sys = (double) myusage.ru_stime.tv_sec +myusage.ru_stime.tv_usec/1000000.0;sys += (double) childusage.ru_stime.tv_sec +childusage.ru_stime.tv_usec/1000000.0;printf("\nuser time = %g, sys time = %g\n", user, sys);
}

web_child.c:

#include  "unp.h"#define    MAXN    16384       /* max # bytes client can request */void
web_child(int sockfd)
{int            ntowrite;ssize_t        nread;char      line[MAXLINE], result[MAXN];for ( ; ; ) {if ( (nread = Readline(sockfd, line, MAXLINE)) == 0)return;     /* connection closed by other end *//* 4line from client specifies #bytes to write back */ntowrite = atol(line);if ((ntowrite <= 0) || (ntowrite > MAXN))err_quit("client request for %d bytes", ntowrite);Writen(sockfd, result, ntowrite);}
}

client.c:

#include "unp.h"#define    MAXN    16384       /* max # bytes to request from server */int
main(int argc, char **argv)
{int        i, j, fd, nchildren, nloops, nbytes;pid_t   pid;ssize_t n;char  request[MAXLINE], reply[MAXN];if (argc != 6)err_quit("usage: client <hostname or IPaddr> <port> <#children> ""<#loops/child> <#bytes/request>");nchildren = atoi(argv[3]);nloops = atoi(argv[4]);nbytes = atoi(argv[5]);snprintf(request, sizeof(request), "%d\n", nbytes); /* newline at end */for (i = 0; i < nchildren; i++) {if ( (pid = Fork()) == 0) {       /* child */for (j = 0; j < nloops; j++) {fd = Tcp_connect(argv[1], argv[2]);Write(fd, request, strlen(request));if ( (n = Readn(fd, reply, nbytes)) != nbytes)err_quit("server returned %d bytes", n);Close(fd);     /* TIME_WAIT on client, not server */}printf("child %d done\n", i);exit(0);}/* parent loops around to fork() again */}while (wait(NULL) > 0)   /* now parent waits for all children */;if (errno != ECHILD)err_sys("wait error");exit(0);
}

server.c:

/* include serv05a */
#include    "unp.h"
#include    "child.h"static int       nchildren;int
main(int argc, char **argv)
{int            listenfd, i, navail, maxfd, nsel, connfd, rc;void       sig_int(int);pid_t      child_make(int, int, int);ssize_t       n;fd_set        rset, masterset;socklen_t   addrlen, clilen;struct sockaddr *cliaddr;if (argc == 3)listenfd = Tcp_listen(NULL, argv[1], &addrlen);else if (argc == 4)listenfd = Tcp_listen(argv[1], argv[2], &addrlen);elseerr_quit("usage: serv05 [ <host> ] <port#> <#children>");FD_ZERO(&masterset);FD_SET(listenfd, &masterset);maxfd = listenfd;cliaddr = Malloc(addrlen);nchildren = atoi(argv[argc-1]);navail = nchildren;cptr = Calloc(nchildren, sizeof(Child));/* 4prefork all the children */for (i = 0; i < nchildren; i++) {child_make(i, listenfd, addrlen);    /* parent returns */FD_SET(cptr[i].child_pipefd, &masterset);maxfd = max(maxfd, cptr[i].child_pipefd);}Signal(SIGINT, sig_int);for ( ; ; ) {rset = masterset;if (navail <= 0)FD_CLR(listenfd, &rset); /* turn off if no available children */nsel = Select(maxfd + 1, &rset, NULL, NULL, NULL);/* 4check for new connections */if (FD_ISSET(listenfd, &rset)) {clilen = addrlen;connfd = Accept(listenfd, cliaddr, &clilen);for (i = 0; i < nchildren; i++)if (cptr[i].child_status == 0)break;               /* available */if (i == nchildren)err_quit("no available children");cptr[i].child_status = 1;  /* mark child as busy */cptr[i].child_count++;navail--;n = Write_fd(cptr[i].child_pipefd, "", 1, connfd);Close(connfd);if (--nsel == 0)continue; /* all done with select() results */}/* 4find any newly-available children */for (i = 0; i < nchildren; i++) {if (FD_ISSET(cptr[i].child_pipefd, &rset)) {if ( (n = Read(cptr[i].child_pipefd, &rc, 1)) == 0)err_quit("child %d terminated unexpectedly", i);cptr[i].child_status = 0;navail++;if (--nsel == 0)break;   /* all done with select() results */}}}
}
/* end serv05a */void
sig_int(int signo)
{int        i;void  pr_cpu_time(void);/* 4terminate all children */for (i = 0; i < nchildren; i++)kill(cptr[i].child_pid, SIGTERM);while (wait(NULL) > 0)      /* wait for all children */;if (errno != ECHILD)err_sys("wait error");pr_cpu_time();for (i = 0; i < nchildren; i++)printf("child %d, %ld connections\n", i, cptr[i].child_count);exit(0);
}

编译命令：

gcc server.c child.c pr_cpu_time.c web_child.c -o server -lunp