本文共 5985 字，大约阅读时间需要 19 分钟。
survey模式是由server发出询问，client针对请求回复响应的一种模式。这种模式在分布式系统中非常有用，
可以用来做服务发现、分布式事物等分布式询问。客户端实现比较方便，除了基础调用（创建socket、连接url）之外，就是先接收服务端询问
（例子中比较简单，服务端询问是固定的，所以没有对内容进行检查）针对询问发送响应 （例子中是发送服务端当前时间）#include#include #include #include #include #include using namespace std;int main(int argc, const char **argv) { if(argc != 3) { fprintf(stderr, "usage: %s NAME URLn", argv[0]); exit(-1); } const char *name = argv[1]; const char *url = argv[2]; int sock = nn_socket(AF_SP, NN_RESPONDENT); if(sock < 0){ fprintf(stderr, "nn_socket fail: %sn", nn_strerror(errno)); exit(-1); } if(nn_connect(sock, url) < 0) { fprintf(stderr, "nn_connect fail: %sn", nn_strerror(errno)); exit(-1); } while(1){ char *buf = NULL; int bytes = nn_recv (sock, &buf, NN_MSG, 0); if(bytes > 0) { printf ("CLIENT (%s): RECEIVED "%s" SURVEY REQUESTn", name, buf); nn_freemsg (buf); char sendBuffer[128]; time_t rawtime; struct tm * timeinfo; time (&rawtime); timeinfo = localtime (&rawtime); char *timeText = asctime (timeinfo); int textLen = strlen(timeText); timeText[textLen - 1] = ''; sprintf(sendBuffer, "[ %s ] %s", name, timeText); int sendSize = strlen(sendBuffer) + 1; int actualSendSize = nn_send(sock, sendBuffer, sendSize, 0); if(actualSendSize != sendSize) { fprintf(stderr, "nn_send fail, expect length %d, actual length %dn", sendSize, actualSendSize); continue; } } } nn_shutdown(sock, 0); return 0;}
这里收到消息后，就简单的打印，然后将响应数据写会给服务端。
服务端有个问题，之前搜索了几个例子都不太正常。经过尝试和简单查看代码之后发现，通过nanomsg基础api，
无法获取当前有多少客户端。但是，如果当前所有连接的客户端的响应都已经收到，再次调用nn_recv之后， 会直接返回-1，表示读取失败，同时errno（通过errno函数获取）被设置为EFSM，表示当前状态机状态不正确。#include#include #include #include #include #include using namespace std;const char *SURVEY_TYPE = "DATE";int main(int argc, char** argv){ if ( argc != 2 ) { fprintf(stderr, "usage: %s URLn", argv[0]); exit(-1); } const char *url = argv[1]; int sock = nn_socket(AF_SP, NN_SURVEYOR); if(sock < 0) { fprintf (stderr, "nn_socket failed: %sn", nn_strerror (errno)); exit(-1); } if(nn_bind(sock, url) < 0) { fprintf(stderr, "nn_bind fail: %sn", nn_strerror(errno)); exit(-1); } while(1) { int sendSize = strlen(SURVEY_TYPE) + 1; int actualSendSize; printf ("SERVER: SENDING DATE SURVEY REQUESTn"); if ((actualSendSize = nn_send(sock, SURVEY_TYPE, sendSize, 0)) != sendSize) { fprintf(stderr, "nn_send fail, expect length %d, actual length %dn", sendSize, actualSendSize); continue; } int count = 0; while(1) { char *buf = NULL; int bytes = nn_recv (sock, &buf, NN_MSG, 0); if (bytes < 0 && nn_errno() == ETIMEDOUT) break; if (bytes >= 0) { printf ("SERVER: RECEIVED "%s" SURVEY RESPONSEn", buf); ++count; nn_freemsg (buf); } else { fprintf(stderr, "nn_recv fail: %sn", nn_strerror(errno)); break; } } printf("SERVER: current receive %d survey response.n", count); sleep(1); } nn_shutdown(sock, 0); return 0;}
这里用了两个死循环，外层循环不停尝试向客户端发起询问。完成询问后，通过另外一个死循环读取所有的客户端响应，
当读取失败时退出循环。之前找到的源码是直接判断错误是否ETIMEDOUT，经过打印会发现每次都没有超时，而是状态机错误：
/* If no survey is going on return EFSM error. */if (nn_slow (!nn_surveyor_inprogress (surveyor))) return -EFSM;
测试和前文差不多，先启动一个server，然后再一个个启动client：
#!/bin/bashBASE="$( cd "$( dirname "$0" )" && pwd )"SERVER=$BASE/surveyserverCLIENT=$BASE/surveyclientURL="tcp://127.0.0.1:1234"echo "start surveyserver to bind tcp: $URL"$SERVER tcp://127.0.0.1:1234 &echo "start to start surveyclient"for((i = 0; i < 10; i++))do echo "start client$i" $CLIENT client$i $URL & sleep 1donesleep 20echo "kill all process and exit"for pid in `jobs -p`do echo "kill $pid" kill $piddonewait
输出为：
start surveyserver to bind tcp: tcp://127.0.0.1:1234start to start surveyclientstart client0SERVER: SENDING DATE SURVEY REQUESTstart client1nn_recv fail: Operation cannot be performed in this stateSERVER: current receive 0 survey response.start client2SERVER: SENDING DATE SURVEY REQUESTCLIENT (client0): RECEIVED "DATE" SURVEY REQUESTSERVER: RECEIVED "[ client0 ] Tue Feb 17 23:32:43 2015" SURVEY RESPONSECLIENT (client1): RECEIVED "DATE" SURVEY REQUESTSERVER: RECEIVED "[ client1 ] Tue Feb 17 23:32:43 2015" SURVEY RESPONSEnn_recv fail: Operation cannot be performed in this stateSERVER: current receive 2 survey response.start client3SERVER: SENDING DATE SURVEY REQUESTCLIENT (client0): RECEIVED "DATE" SURVEY REQUESTCLIENT (client1): RECEIVED "DATE" SURVEY REQUESTCLIENT (client2): RECEIVED "DATE" SURVEY REQUEST...SERVER: SENDING DATE SURVEY REQUESTCLIENT (client0): RECEIVED "DATE" SURVEY REQUESTCLIENT (client1): RECEIVED "DATE" SURVEY REQUESTCLIENT (client2): RECEIVED "DATE" SURVEY REQUESTCLIENT (client3): RECEIVED "DATE" SURVEY REQUESTCLIENT (client4): RECEIVED "DATE" SURVEY REQUESTCLIENT (client5): RECEIVED "DATE" SURVEY REQUESTCLIENT (client6): RECEIVED "DATE" SURVEY REQUESTCLIENT (client7): RECEIVED "DATE" SURVEY REQUESTCLIENT (client9): RECEIVED "DATE" SURVEY REQUESTCLIENT (client8): RECEIVED "DATE" SURVEY REQUESTSERVER: RECEIVED "[ client0 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client1 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client2 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client3 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client4 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client5 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client6 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client7 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client9 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSESERVER: RECEIVED "[ client8 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSEnn_recv fail: Operation cannot be performed in this stateSERVER: current receive 10 survey response.
从输出可以看见，每次最后一个接收完成之后，都会有一个“Operation cannot be performed in this state”
错误，也就是EFSM错误。转载自：https://coolex.info/blog/495.html