[英]Using select() for non-blocking sockets
我正在嘗試使用 select function 在服務器和 1 個客戶端(不再有)之間進行非阻塞 i/o,其中通信流暢(可以隨時發送,另一個將接收而無需等待發送)。 我找到了一個包含一些代碼的教程,並試圖將其改編為我的。 這就是我所擁有的——
服務器
#define PORT "4950"
#define STDIN 0
struct sockaddr name;
void set_nonblock(int socket) {
int flags;
flags = fcntl(socket,F_GETFL,0);
assert(flags != -1);
fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
if (sa->sa_family == AF_INET)
return &(((struct sockaddr_in*)sa)->sin_addr);
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(int agrc, char** argv) {
int status, sock, adrlen, new_sd;
struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results
//store the connecting address and size
struct sockaddr_storage their_addr;
socklen_t their_addr_size;
fd_set read_flags,write_flags; // the flag sets to be used
struct timeval waitd; // the max wait time for an event
int sel; // holds return value for select();
//socket infoS
memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address
//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
//make socket
sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (sock < 0) {
printf("\nserver socket failure %m", errno);
exit(1);
}
//allow reuse of port
int yes=1;
if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
//unlink and bind
unlink("127.0.0.1");
if(bind (sock, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
printf("\nBind error %m", errno);
exit(1);
}
freeaddrinfo(servinfo);
//listen
if(listen(sock, 5) < 0) {
printf("\nListen error %m", errno);
exit(1);
}
their_addr_size = sizeof(their_addr);
//accept
new_sd = accept(sock, (struct sockaddr*)&their_addr, &their_addr_size);
if( new_sd < 0) {
printf("\nAccept error %m", errno);
exit(1);
}
set_nonblock(new_sd);
cout<<"\nSuccessful Connection!";
char* in = new char[255];
char* out = new char[255];
int numSent;
int numRead;
while(1) {
waitd.tv_sec = 10;
FD_ZERO(&read_flags);
FD_ZERO(&write_flags);
FD_SET(new_sd, &read_flags);
if(strlen(out) != 0)
FD_SET(new_sd, &write_flags);
sel = select(new_sd+1, &read_flags, &write_flags, (fd_set*)0, &waitd);
if(sel < 0)
continue;
//socket ready for reading
if(FD_ISSET(new_sd, &read_flags)) {
FD_CLR(new_sd, &read_flags);
memset(&in, 0, sizeof(in));
if(recv(new_sd, in, sizeof(in), 0) <= 0) {
close(new_sd);
break;
}
else
cout<<"\n"<<in;
} //end if ready for read
//socket ready for writing
if(FD_ISSET(new_sd, &write_flags)) {
FD_CLR(new_sd, &write_flags);
send(new_sd, out, strlen(out), 0);
memset(&out, 0, sizeof(out));
}
} //end while
cout<<"\n\nExiting normally\n";
return 0;
}
客戶(基本上相同,只是減去了一個接受呼叫) -
#define PORT "4950"
struct sockaddr name;
void set_nonblock(int socket) {
int flags;
flags = fcntl(socket,F_GETFL,0);
assert(flags != -1);
fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
if (sa->sa_family == AF_INET)
return &(((struct sockaddr_in*)sa)->sin_addr);
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(int agrc, char** argv) {
int status, sock, adrlen;
struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results
fd_set read_flags,write_flags; // the flag sets to be used
struct timeval waitd; // the max wait time for an event
int sel; // holds return value for select();
memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address
//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
//make socket
sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (sock < 0) {
printf("\nserver socket failure %m", errno);
exit(1);
}
if(connect(sock, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
printf("\nclient connection failure %m", errno);
exit(1);
}
cout<<"\nSuccessful connection!";
set_nonblock(sock);
char* out = new char[255];
char* in = new char[255];
int numRead;
int numSent;
while(1) {
waitd.tv_sec = 10;
FD_ZERO(&read_flags);
FD_ZERO(&write_flags);
FD_SET(sock, &read_flags);
if(strlen(out) != 0)
FD_SET(sock, &write_flags);
sel = select(sock+1, &read_flags, &write_flags, (fd_set*)0, &waitd);
if(sel < 0)
continue;
//socket ready for reading
if(FD_ISSET(sock, &read_flags)) {
FD_CLR(sock, &read_flags);
memset(&in, 0, sizeof(in));
if(recv(sock, in, sizeof(in), 0) <= 0) {
close(sock);
break;
}
else
cout<<"\n"<<in;
} //end if ready for read
//socket ready for writing
if(FD_ISSET(sock, &write_flags)) {
FD_CLR(sock, &write_flags);
send(sock, out, strlen(out), 0);
memset(&out, 0, sizeof(out));
}
} //end while
cout<<"\n\nExiting normally\n";
return 0;
}
問題是當我運行它們時,什么也沒有發生。 我可以輸入一個並按回車鍵,而另一個屏幕上什么也沒有顯示(反之亦然)。 這不是我要調試的全部信息,這是我第一次真正嘗試使用 select 所以我想也許我只是不知道一些簡單的事情。 如果有任何發現是錯誤或奇怪的,請指出,任何幫助表示贊賞。
問題是當我運行它們時,什么也沒有發生。
真正的問題是人們多年來一直在粘貼 Beej 的東西而不理解它。 這就是為什么我不太喜歡那個指南。 它給出了大塊代碼而沒有真正詳細解釋它們。
您沒有閱讀任何內容,也沒有發送任何內容; 沒有 fgets、scanf、cin 等。這就是我要做的:
FD_SET(sock, &read_flags);
FD_SET(STDIN_FILENO, &read_flags);
/* .. snip .. */
if(FD_ISSET(STDIN_FILENO, &read_flags)) {
fgets(out, len, stdin);
}
這將監視stdin
並在輸入可用時從中讀取; 然后,當套接字可寫時( FD_ISSET(sock, &write_flags)
),它將發送緩沖區。
我的程序現在可以正常工作。
服務器 -
#define PORT "4950"
#define STDIN 0
struct sockaddr name;
void set_nonblock(int socket) {
int flags;
flags = fcntl(socket,F_GETFL,0);
assert(flags != -1);
fcntl(socket, F_SETFL, flags | O_NONBLOCK);
}
// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa) {
if (sa->sa_family == AF_INET)
return &(((struct sockaddr_in*)sa)->sin_addr);
return &(((struct sockaddr_in6*)sa)->sin6_addr);
}
int main(int agrc, char** argv) {
int status, sock, adrlen, new_sd;
struct addrinfo hints;
struct addrinfo *servinfo; //will point to the results
//store the connecting address and size
struct sockaddr_storage their_addr;
socklen_t their_addr_size;
fd_set read_flags,write_flags; // the flag sets to be used
struct timeval waitd = {10, 0}; // the max wait time for an event
int sel; // holds return value for select();
//socket infoS
memset(&hints, 0, sizeof hints); //make sure the struct is empty
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM; //tcp
hints.ai_flags = AI_PASSIVE; //use local-host address
//get server info, put into servinfo
if ((status = getaddrinfo("127.0.0.1", PORT, &hints, &servinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
//make socket
sock = socket(servinfo->ai_family, servinfo->ai_socktype, servinfo->ai_protocol);
if (sock < 0) {
printf("\nserver socket failure %m", errno);
exit(1);
}
//allow reuse of port
int yes=1;
if (setsockopt(sock,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int)) == -1) {
perror("setsockopt");
exit(1);
}
//unlink and bind
unlink("127.0.0.1");
if(bind (sock, servinfo->ai_addr, servinfo->ai_addrlen) < 0) {
printf("\nBind error %m", errno);
exit(1);
}
freeaddrinfo(servinfo);
//listen
if(listen(sock, 5) < 0) {
printf("\nListen error %m", errno);
exit(1);
}
their_addr_size = sizeof(their_addr);
//accept
new_sd = accept(sock, (struct sockaddr*)&their_addr, &their_addr_size);
if( new_sd < 0) {
printf("\nAccept error %m", errno);
exit(1);
}
//set non blocking
set_nonblock(new_sd);
cout<<"\nSuccessful Connection!\n";
char in[255];
char out[255];
memset(&in, 0, 255);
memset(&out, 0, 255);
int numSent;
int numRead;
while(1) {
FD_ZERO(&read_flags);
FD_ZERO(&write_flags);
FD_SET(new_sd, &read_flags);
FD_SET(new_sd, &write_flags);
FD_SET(STDIN_FILENO, &read_flags);
FD_SET(STDIN_FILENO, &write_flags);
sel = select(new_sd+1, &read_flags, &write_flags, (fd_set*)0, &waitd);
//if an error with select
if(sel < 0)
continue;
//socket ready for reading
if(FD_ISSET(new_sd, &read_flags)) {
//clear set
FD_CLR(new_sd, &read_flags);
memset(&in, 0, 255);
numRead = recv(new_sd, in, 255, 0);
if(numRead <= 0) {
printf("\nClosing socket");
close(new_sd);
break;
}
else if(in[0] != '\0')
cout<<"\nClient: "<<in;
} //end if ready for read
//if stdin is ready to be read
if(FD_ISSET(STDIN_FILENO, &read_flags))
fgets(out, 255, stdin);
//socket ready for writing
if(FD_ISSET(new_sd, &write_flags)) {
//printf("\nSocket ready for write");
FD_CLR(new_sd, &write_flags);
send(new_sd, out, 255, 0);
memset(&out, 0, 255);
} //end if
} //end while
cout<<"\n\nExiting normally\n";
return 0;
}
客戶基本上是一樣的......唯一的區別是缺乏傾聽和接受。
我只想補充一點,上述示例在 Linux 上可能無法按預期工作。 在 Linux 上,waitd 可能被 select 修改。 所以對於 Linux,waitd 應該在 select 之前重寫。
請參閱 select 手冊頁中的“超時”部分。
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