Socket, Network programming

#include <sys/socket.h>
int listen(int sockfd, int backlog);

                                    /* Returns 0 on success, or –1 on error */

#include <sys/socket.h>
int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);

                      /* Returns file descriptor on success, or –1 on error */

// file mytimesrv.c: A time server
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <time.h>

int main(int argc, char **argv)
{
  int     listenfd, connfd;
  socklen_t len;
  struct sockaddr_in servaddr, cliaddr;
  char    buff[1024];
  time_t  ticks;

  if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    perror ("socket");
    exit (1);
  }

  memset(&servaddr, 0, sizeof (servaddr));
  servaddr.sin_family = AF_INET;
  servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  servaddr.sin_port = htons(13000);                     /* daytime server */

  if (bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {
    perror("bind");
    exit (1);
  }

  if (listen(listenfd, SOMAXCONN) < 0) {
    perror("listen");
    exit (1);
  }

  for ( ; ; ) {
    len = sizeof(cliaddr);
    if ((connfd = accept(listenfd, (struct sockaddr *) &cliaddr, &len)) < 0) {
      perror ("accept");
      exit (1);
    }
    printf("connection from %s, port %d\n",
           inet_ntop(AF_INET, &cliaddr.sin_addr, buff, sizeof(buff)),
           ntohs(cliaddr.sin_port));

    ticks = time(NULL);
    snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));

    write(connfd, buff, strlen(buff));
    close(connfd);
  }
}

/* 只演示了核心代码逻辑。比如没有wait子进程（防止子进程成为zombie process）等代码 */

for (;;) {
  cfd = accept(lfd, NULL, NULL);     /* Wait for connection */
  if (cfd == -1) {
    perror("accept");
    exit(EXIT_FAILURE);
  }

  /* Handle each client request in a new child process */
  switch (fork()) {         /* fork后，“监听套接字”和“已连接套接字”都会共享 */
  case -1:
    syslog(LOG_ERR, "Can't create child (%s)", strerror(errno));
    close(cfd);             /* Give up on this client */
    break;                  /* May be temporary; try next client */
  case 0:    /* Child */
    close(lfd);             /* “监听套接字”在父进程中处理，子进程中应该close它 */
    handleRequest(cfd);     /* 实际处理代码在handleRequest函数中 */
    exit(EXIT_SUCCESS);
  default:  /* Parent */
    close(cfd);             /* “已连接套接字”会在子进程中处理，父进程中应该close它（即引用计数减1） */
    break;                  /* Loop to accept next connection */
  }
 }

            /* --- begin of keepalive test program --- */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

int main(void);

int main()
{
   int s;
   int optval;
   socklen_t optlen = sizeof(optval);

   /* Create the socket */
   if((s = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
      perror("socket()");
      exit(EXIT_FAILURE);
   }

   /* Check the status for the keepalive option */
   if(getsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE is %s\n", (optval ? "ON" : "OFF"));

   /* Set the option active */
   optval = 1;
   optlen = sizeof(optval);
   if(setsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, optlen) < 0) {
      perror("setsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE set on socket\n");

   /* Check the status again */
   if(getsockopt(s, SOL_SOCKET, SO_KEEPALIVE, &optval, &optlen) < 0) {
      perror("getsockopt()");
      close(s);
      exit(EXIT_FAILURE);
   }
   printf("SO_KEEPALIVE is %s\n", (optval ? "ON" : "OFF"));

   close(s);

   exit(EXIT_SUCCESS);
}

            /* ---  end of keepalive test program  --- */

#include <sys/select.h>

int select(int maxfdp1,                     /* 最大文件描述符编号值加1 */
           fd_set *restrict readfds,        /* 既是输入参数，又是输出参数 */
           fd_set *restrict writefds,       /* 既是输入参数，又是输出参数 */
           fd_set *restrict exceptfds,      /* 既是输入参数，又是输出参数 */
           struct timeval *restrict tvptr); /* 愿意等待的时间（也可能是输出参数） */

           /* Returns: count of ready descriptors, 0 on timeout, −1 on error */

#include <poll.h>
int poll(struct pollfd fdarray[], nfds_t nfds, int timeout);

           /* Returns: count of ready descriptors, 0 on timeout, −1 on error */

struct pollfd {
  int fd;          /* file descriptor to check, or < 0 to ignore */
  short events;    /* (输入参数) events of interest on fd */
  short revents;   /* (输出参数) events that occurred on fd */
};

// file myserv.c: A time server
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>

#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>

typedef struct _worker_info {    /* 每个线程都关联这样一个结构 */
  int connfd;             /* 保存“已连接套接字”（由accept返回）
                             初始值为-1，当工作线程在该套接字上的工作完成后也设为-1
                             它的可能值为-1（当前线程闲），或大于0的值（当前线程忙）
                             对它的访问要加锁 */
  pthread_mutex_t lock;   /* 互斥量，用于对connfd的访问加锁 */
  pthread_cond_t cond;    /* 条件变量，用于管理空闲的线程（让它阻塞，或者唤醒它） */

  /* other information */
  pthread_t tid;
} worker_info;


worker_info workers[128];     /* 假设线程数不会大于128 */
int threads_num = 3;          /* 默认的线程数量 */

sem_t sem;                    /* 这个信号量管理可用的线程数 */

void * thread_fn(void *arg);
int request_worker();

int main(int argc, char **argv) {
  short int port;

  if (argc == 2) {
    port = atoi(argv[1]);
  } else if (argc == 3) {
    port = atoi(argv[1]);
    threads_num = atoi(argv[2]);
  } else {
    fprintf(stderr, "%s", "Usage: myserv port [thread_num]\n"); exit(1);
  }

  /* 第1步：创建socket，绑定、监听到指定端口 */
  int listenfd, connfd;
  struct sockaddr_in servaddr;

  if ((listenfd = socket(AF_INET, SOCK_STREAM, 0)) < 0) {
    perror("socket"); exit(1);
  }

  memset(&servaddr, 0, sizeof(servaddr));
  servaddr.sin_family = AF_INET;
  servaddr.sin_addr.s_addr = htonl(INADDR_ANY);
  servaddr.sin_port = htons(port);

  if (bind(listenfd, (struct sockaddr *) &servaddr, sizeof(servaddr)) < 0) {
    perror("bind"); exit (1);
  }

  if (listen(listenfd, SOMAXCONN) < 0) {
    perror("listen"); exit (1);
  }

  /* 第2步：创建线程池 */
  int i;
  for (i=0; i < threads_num; i++) {

    /* 准备好传递给线程的参数 */
    workers[i].connfd = -1;
    pthread_mutex_init(&workers[i].lock, NULL);
    pthread_cond_init(&workers[i].cond, NULL);

    /* 创建线程 */
    if (pthread_create(&workers[i].tid, NULL, thread_fn, (void *)(workers + i)) != 0) {
      perror("pthread_create"); exit(1);
    }

  }

  sem_init(&sem, 0, threads_num);      /* 初始信号量为所创建的线程数 */

  /* 第3步：为每个“客户连接”分配一个空闲线程进行处理 */
  int slot;
  int clientfd;
  for( ; ; ) {

    slot = request_worker();           /* 寻找空闲的线程，找不到会阻塞 */

    if ((clientfd = accept(listenfd, NULL, NULL)) < 0) {
      perror("accept"); exit(1);
    }

    pthread_mutex_lock(&workers[slot].lock);
    workers[slot].connfd = clientfd;
    pthread_mutex_unlock(&workers[slot].lock);

    /* 唤醒这个空闲的线程 */
    pthread_cond_signal(&workers[slot].cond);
  }

  return 0;
}

/* 在线程池中寻找一个空闲线程，当没有空闲线程时会阻塞 */
int request_worker() {
  sem_wait(&sem);                    /* 仅当有空闲线程时，才会返回 */

  int i;
  int found = 0;
  for (i=0; i < threads_num; i++) {
    if (workers[i].connfd == -1) {
      found = 1;
      break;
    }
  }
  assert(found == 1);
  return i;
}

/* 业务逻辑（对socket的读写操作）都在这里 */
void doit(int sockfd) {
  char    buff[1024];
  time_t  ticks;

  ticks = time(NULL);
  snprintf(buff, sizeof(buff), "%.24s\r\n", ctime(&ticks));
  write(sockfd, buff, strlen(buff));

  close(sockfd);

  /*  sleep(1);   */
  fprintf(stdout, "server log: do work.\n");
}

/* 线程启动函数 */
void * thread_fn(void *arg) {
  worker_info *info = (worker_info *)arg;

  for( ; ; ) {
    pthread_mutex_lock(&info->lock);
    while(info->connfd == -1) {
      pthread_cond_wait(&info->cond, &info->lock);
      /* pthread_cond_wait有3个作用：
         (1) 解锁互斥量info->lock
         (2) 阻塞线程直到另外的线程通过条件变量info->cond唤醒它
         (3) 再次对互斥量info->lock加锁 */

    }

    doit(info->connfd);        /* Do some work with this connection */

    info->connfd = -1;
    pthread_mutex_unlock(&info->lock);

    sem_post(&sem);            /* 信号量加1（空闲线程多了1个） */
  }
}