nanomsg实验——survey
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
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 <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <nanomsg/nn.h>
#include <nanomsg/survey.h>
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
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 <cstdio>
#include <cstdlib>
#include <cstring>
#include <unistd.h>
#include <nanomsg/nn.h>
#include <nanomsg/survey.h>
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
测试和前文差不多，先启动一个server，然后再一个个启动client：
#!/bin/bash
BASE="$( cd "$( dirname "$0" )" && pwd )"
SERVER=$BASE/surveyserver
CLIENT=$BASE/surveyclient
URL="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 1
done
sleep 20
echo "kill all process and exit"
for pid in `jobs -p`
do
echo "kill $pid"
kill $pid
done
wait
输出为：
start surveyserver to bind tcp: tcp://127.0.0.1:1234
start to start surveyclient
start client0
SERVER: SENDING DATE SURVEY REQUEST
start client1
nn_recv fail: Operation cannot be performed in this state
SERVER: current receive 0 survey response.
start client2
SERVER: SENDING DATE SURVEY REQUEST
CLIENT (client0): RECEIVED "DATE" SURVEY REQUEST
SERVER: RECEIVED "[ client0 ] Tue Feb 17 23:32:43 2015" SURVEY RESPONSE
CLIENT (client1): RECEIVED "DATE" SURVEY REQUEST
SERVER: RECEIVED "[ client1 ] Tue Feb 17 23:32:43 2015" SURVEY RESPONSE
nn_recv fail: Operation cannot be performed in this state
SERVER: current receive 2 survey response.
start client3
SERVER: SENDING DATE SURVEY REQUEST
CLIENT (client0): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client1): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client2): RECEIVED "DATE" SURVEY REQUEST
...
SERVER: SENDING DATE SURVEY REQUEST
CLIENT (client0): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client1): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client2): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client3): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client4): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client5): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client6): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client7): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client9): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client8): RECEIVED "DATE" SURVEY REQUEST
SERVER: RECEIVED "[ client0 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client1 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client2 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client3 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client4 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client5 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client6 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client7 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client9 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
SERVER: RECEIVED "[ client8 ] Tue Feb 17 23:33:09 2015" SURVEY RESPONSE
nn_recv fail: Operation cannot be performed in this state
SERVER: 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。