本节所使用的方式是将非阻塞式I/O与I/O多路复用结合，采用类似事件出发的机制对I/O操作进行处理；与多进程和多线程技术相比，异步I/O技术的最大优势是系统开销小，系统不必创建进程/线程，也不必维护这些进程/线程，从而减少了系统的开销。
1 /** 2 client.c 3 */ 4 #include <stdio.h> 5 #include <unistd.h> 6 #include <string.h> 7 #include <strings.h> 8 #include <sys/types.h> 9 #include <sys/socket.h> 10 #include <netinet/in.h> 11 #include <arpa/inet.h> 12 13 #define PORT 8111 14 #define MSG_LEN 1024 15 16 int main(int argc, char* argv[]) 17 { 18 if (argc != 2) { 19 printf("usage: ./%s <ipaddress> ", argv[0]); 20 return 1; 21 } 22 23 int ret = -1; 24 int socket_fd; 25 socklen_t addr_len; 26 struct sockaddr_in serv_addr; 27 char send_buf[MSG_LEN] = { 0 }; 28 char recv_buf[MSG_LEN] = { 0 }; 29 30 socket_fd = socket(AF_INET, SOCK_STREAM, 0); 31 if (socket_fd < 0) { 32 printf("create socket fd failed. "); 33 _exit(-1); 34 } 35 36 bzero(&serv_addr, sizeof(serv_addr)); 37 serv_addr.sin_family = AF_INET; 38 serv_addr.sin_port = htons(PORT); 39 serv_addr.sin_addr.s_addr = inet_addr(argv[1]); 40 addr_len = sizeof(struct sockaddr); 41 ret = connect(socket_fd, (struct sockaddr *)&serv_addr, addr_len); 42 if (ret < 0) { 43 printf("connect to server[%s:%d] failed. ", argv[1], PORT); 44 _exit(-1); 45 } 46 47 while (1) { 48 memset(send_buf, 0, sizeof(send_buf)); 49 memset(recv_buf, 0, sizeof(recv_buf)); 50 gets(send_buf); 51 52 if (strncmp(send_buf, "quit", 4) == 0) 53 break; 54 55 ret = send(socket_fd, (void *)send_buf, strlen(send_buf), 0); 56 if (ret < 0) { 57 printf("send msg[%s] failed. ", send_buf); 58 break; 59 } 60 61 ret = recv(socket_fd, (void *)recv_buf, sizeof(recv_buf), 0); 62 if (ret < 0) { 63 printf("receive zero msg. "); 64 continue; 65 } 66 67 recv_buf[ret] = ' '; 68 printf("recv msg[%s] ", recv_buf); 69 } 70 71 close(socket_fd); 72 73 return 0; 74 } 75 76 # gcc -std=c11 -g -o client client.c 77 # ./client <ipaddress>
1.fork
1.每收到一个连接就创建一个子进程
2.父进程负责接收连接
3.通过fork创建子进程
1 /** 2 fork.c 3 */ 4 5 #include <stdio.h> 6 #include <unistd.h> 7 #include <string.h> 8 #include <strings.h> 9 #include <sys/types.h> 10 #include <sys/socket.h> 11 #include <netinet/in.h> 12 13 #define PORT 8111 14 #define MSG_LEN 1024 15 16 int main(int argc, char* argv[]) 17 { 18 int ret = -1; 19 int on = 1; 20 int backlog = 10; 21 pid_t pid; 22 int socket_fd, accept_fd; 23 struct sockaddr_in local_addr, remote_addr; 24 char buff[MSG_LEN] = { 0 }; 25 26 socket_fd = socket(AF_INET, SOCK_STREAM, 0); 27 if (socket_fd < 0) { 28 printf("create socket fd failed. "); 29 _exit(-1); 30 } 31 32 ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)); 33 if (ret < 0) { 34 printf("set socket option failed. "); 35 } 36 37 bzero(&local_addr, sizeof(local_addr)); 38 local_addr.sin_family = AF_INET; 39 local_addr.sin_port = htons(PORT); 40 local_addr.sin_addr.s_addr = htonl(INADDR_ANY); 41 ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr)); 42 if (ret < 0) { 43 printf("bind port[%d] failed. ", PORT); 44 _exit(-1); 45 } 46 47 ret = listen(socket_fd, backlog); 48 if (ret < 0) { 49 printf("listen socket[%d] port[%d] failed. ", socket_fd, PORT); 50 _exit(-1); 51 } 52 printf("listening on port[%d]... ", PORT); 53 54 while (1) { 55 socklen_t addr_len = sizeof(struct sockaddr); 56 accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, &addr_len); 57 printf("connection[%d] estasblished... ", accept_fd); 58 59 pid_t pid = fork(); 60 if (pid == 0) { 61 while (1) { 62 memset((void *)buff, 0, sizeof(buff)); 63 ret = recv(accept_fd, (void *)buff, MSG_LEN, 0); 64 if (ret == 0) 65 break; 66 67 buff[ret] = ' '; 68 printf("recv[%s] ", buff); 69 send(accept_fd, (void *)buff, strlen(buff), 0); 70 } 71 72 close(accept_fd); 73 } else { 74 75 } 76 } 77 78 if (pid != 0) 79 close(socket_fd); 80 81 return 0; 82 } 83 84 # gcc -std=c11 -g -o fork fork.c 85 # ./fork
存在问题：
1.资源长期被占用
2.创建子进程耗时
2.select
1.遍历文件描述符集中的所有描述符，找出有变化的描述符
2.对于侦听的socket和数据处理的socket要区别对待
3.socket必须设置为非阻塞的方式工作
4.FD_ZERO()/FD_SET()/FD_ISSET()/FD_CLR()
5.int fcntl(int fd, int cmd, ... /* arg */ ); // flag fcntl(fd, F_SETFL/F_GETFL, flag);
6. int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);
1 /** 2 select.c 3 */ 4 5 /** 6 * struct timeval { 7 * long tv_sec; 8 * long tv_usec; 9 * } 10 */ 11 12 #include <stdio.h> 13 #include <errno.h> 14 #include <unistd.h> 15 #include <fcntl.h> 16 #include <string.h> 17 #include <strings.h> 18 #include <sys/types.h> 19 #include <sys/time.h> 20 #include <sys/socket.h> 21 #include <netinet/in.h> 22 #include <sys/select.h> 23 24 #define PORT 8111 25 #define MSG_LEN 1024 26 #define FD_SIZE 1024 27 28 int main(int argc, char* argv[]) 29 { 30 int ret = -1; 31 int on = 1; 32 int backlog = 10; 33 int flags; 34 int events = 0; 35 int max_fd = -1; 36 fd_set fd_sets; 37 struct timeval time_out = {3, 0}; 38 int accept_fds[FD_SIZE] = { 0 }; 39 memset(accept_fds, -1, sizeof(accept_fds)); 40 int socket_fd; 41 struct sockaddr_in local_addr, remote_addr; 42 char buff[MSG_LEN] = { 0 }; 43 44 socket_fd = socket(AF_INET, SOCK_STREAM, 0); 45 if (socket_fd < 0) { 46 printf("create socket fd failed. "); 47 _exit(-1); 48 } 49 50 max_fd = socket_fd; 51 52 flags = fcntl(socket_fd, F_GETFL, 0); 53 fcntl(socket_fd, F_SETFL, flags | O_NONBLOCK); 54 55 ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)); 56 if (ret < 0) { 57 printf("set socket option failed. "); 58 } 59 60 bzero(&local_addr, sizeof(local_addr)); 61 local_addr.sin_family = AF_INET; 62 local_addr.sin_port = htons(PORT); 63 local_addr.sin_addr.s_addr = htonl(INADDR_ANY); 64 ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr)); 65 if (ret < 0) { 66 printf("bind port[%d] failed. ", PORT); 67 _exit(-1); 68 } 69 70 ret = listen(socket_fd, backlog); 71 if (ret < 0) { 72 printf("listen socket[%d] port[%d] failed. ", socket_fd, PORT); 73 _exit(-1); 74 } 75 printf("listening on port[%d]... ", PORT); 76 77 while (1) { 78 FD_ZERO(&fd_sets); 79 FD_SET(socket_fd, &fd_sets); 80 max_fd = socket_fd; 81 /*for (const int& accept_fd : accept_fds) { 82 if (accept_fd == -1) 83 continue; 84 85 if (accept_fd > max_fd) 86 max_fd = accept_fd; 87 88 printf("accept fd:%d ", accept_fd); 89 FD_SET(accept_fd, &fd_sets); 90 }*/ 91 for (int i = 0; i < FD_SIZE; ++i) { 92 if (accept_fds[i] == -1) 93 continue; 94 95 if (accept_fds[i] > max_fd) 96 max_fd = accept_fds[i]; 97 98 FD_SET(accept_fds[i], &fd_sets); 99 } 100 101 time_out.tv_sec = 2; // 2 seconds 102 time_out.tv_usec = 500000; // 500 micro second 103 events = select(max_fd + 1, &fd_sets, NULL, NULL, &time_out); 104 if (events < 0) { 105 printf("select[%d] errno[%d|%s] ", events, errno, strerror(errno)); 106 for (int i = 0; i < FD_SIZE; ++i) { 107 if (accept_fds[i] == -1) 108 continue; 109 110 if (FD_ISSET(accept_fds[i], &fd_sets)) { 111 char buf[MSG_LEN] = { 0 }; 112 int n = read(accept_fds[i], buf, MSG_LEN); 113 if (n <= 0 && errno == EBADF) { // errno important 114 printf("n:%d], fd:%d], errno[%d|%s] ", n, accept_fds[i], errno, strerror(errno)); 115 close(accept_fds[i]); 116 FD_CLR(accept_fds[i], &fd_sets); 117 accept_fds[i] = -1; 118 } 119 } 120 } 121 continue; 122 } else if (events == 0) { 123 printf("select timeout "); 124 continue; 125 } else if (events > 0) { 126 if (FD_ISSET(socket_fd, &fd_sets)) { 127 int curpos = -1; 128 for (int i = 0; i < FD_SIZE; ++i) { 129 if (accept_fds[i] == -1) { 130 curpos = i; 131 break; 132 } 133 } 134 135 if (curpos != -1) { 136 socklen_t addr_len = sizeof(struct sockaddr); 137 int accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, &addr_len); 138 printf("connection[%d] estasblished... ", accept_fd); 139 140 flags = fcntl(accept_fd, F_GETFL, 0); 141 fcntl(accept_fd, F_SETFL, flags | O_NONBLOCK); 142 accept_fds[curpos] = accept_fd; 143 } else { 144 printf("fd slots fills. "); 145 } 146 } 147 148 for (int i = 0; i < FD_SIZE; ++i) { 149 if (accept_fds[i] != -1 && FD_ISSET(accept_fds[i], &fd_sets)) { 150 memset(buff, 0, sizeof(buff)); 151 ret = recv(accept_fds[i], (void *)buff, sizeof(buff), 0); 152 if (ret == 0) { 153 close(accept_fds[i]); 154 continue; 155 } 156 157 printf("recv[%s] ", buff); 158 send(accept_fds[i], (void *)buff, strlen(buff), 0); 159 } 160 } 161 } 162 } 163 164 close(socket_fd); 165 166 return 0; 167 } 168 169 # gcc -std=c11 -g -o select select.c 170 # ./select
3.poll
1.#include <poll.h>
2.int poll(struct pollfd *fds, nfds_t nfds, int timeout);
3.POLLIN/POLLOUT/POLLERR
1 /** 2 poll.c 3 */ 4 5 /** 6 * struct pollfd { 7 * int fd; 8 * short events; 9 * short revents; 10 * }; 11 */ 12 13 #include <stdio.h> 14 #include <unistd.h> 15 #include <string.h> 16 #include <strings.h> 17 #include <sys/types.h> 18 #include <sys/socket.h> 19 #include <netinet/in.h> 20 #include <poll.h> 21 #include <errno.h> 22 #include <limits.h> 23 24 #define PORT 8111 25 #define MSG_LEN 1024 26 #define OPEN_MAX 1024 27 #define INFTIM -1 28 29 int main(int argc, char* argv[]) 30 { 31 int ret = -1; 32 int on = 1; 33 int backlog = 10; 34 int maxi = -1; 35 int socket_fd, accept_fd; 36 struct sockaddr_in local_addr, remote_addr; 37 char buff[MSG_LEN] = { 0 }; 38 struct pollfd client[OPEN_MAX]; 39 40 socket_fd = socket(AF_INET, SOCK_STREAM, 0); 41 if (socket_fd < 0) { 42 printf("create socket fd failed. "); 43 _exit(-1); 44 } 45 46 ret = setsockopt(socket_fd, SOL_SOCKET, SO_REUSEADDR, &on, sizeof(on)); 47 if (ret < 0) { 48 printf("set socket option failed. "); 49 } 50 51 bzero(&local_addr, sizeof(local_addr)); 52 local_addr.sin_family = AF_INET; 53 local_addr.sin_port = htons(PORT); 54 local_addr.sin_addr.s_addr = htonl(INADDR_ANY); 55 ret = bind(socket_fd, (struct sockaddr *)&local_addr, sizeof(struct sockaddr)); 56 if (ret < 0) { 57 printf("bind port[%d] failed. ", PORT); 58 _exit(-1); 59 } 60 61 ret = listen(socket_fd, backlog); 62 if (ret < 0) { 63 printf("listen socket[%d] port[%d] failed. ", socket_fd, PORT); 64 _exit(-1); 65 } 66 printf("listening on port[%d]... ", PORT); 67 68 client[0].fd = socket_fd; 69 client[0].events = POLLIN; 70 for (int i = 1; i < OPEN_MAX; ++i) { 71 client[i].fd = -1; 72 } 73 maxi = 0; 74 75 while (1) { 76 ret = poll(client, maxi + 1, INFTIM); 77 if (client[0].revents & POLLIN) { 78 socklen_t addr_len = sizeof(struct sockaddr); 79 accept_fd = accept(socket_fd, (struct sockaddr *)&remote_addr, &addr_len); 80 int i = -1; 81 for (i = 1; i < OPEN_MAX; ++i) { 82 if (client[i].fd < 0) { 83 client[i].fd = accept_fd; 84 break; 85 } 86 } 87 88 if (i == OPEN_MAX) { 89 printf("connection[%d] fill ", OPEN_MAX); 90 continue; 91 } 92 93 client[i].events = POLLIN; 94 if (i > maxi) 95 maxi = i; 96 97 printf("connection[%d] estasblished... ", accept_fd); 98 } 99 100 for (int i = 1; i < OPEN_MAX; ++i) { 101 if (client[i].fd < 0) 102 continue; 103 104 if (client[i].revents & (POLLIN | POLLERR)) { 105 ret = read(client[i].fd, buff, sizeof(buff)); 106 if (ret == 0 || (ret < 0 && errno == EBADF)) { 107 close(client[i].fd); 108 client[i].fd = -1; 109 } else { 110 buff[ret] = ' '; 111 printf("recv[%s] ", buff); 112 write(client[i].fd, (void *)buff, strlen(buff)); 113 } 114 } 115 } 116 } 117 118 close(socket_fd); 119 120 return 0; 121 } 122 123 # gcc -std=c11 -g -o poll poll.c 124 # ./poll
select和poll模型都存在的一个问题就是需要剔除异常的socket文件描述符，否则程序会不停报错。