socket设置超时遇到的问题

2009-03-15 06:02:22 267 阅读 AI 写同款 · GEO 优化AI 选题数据监测一键分发 ›

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我使用了setsockopt设置超时，如下：
timeout = 20;//20ms
bread = setsockopt(sockRaw,SOL_SOCKET,SO_RCVTIMEO,(char*)&timeout,sizeof(timeout));
if(bread == SOCKET_ERROR) {
fprintf(stderr,"failed to set recv timeout: %d\n",WSAGetLastError());
ExitProcess(STATUS_FAILED);
}
timeout = 20; //20ms
bread = setsockopt(sockRaw,SOL_SOCKET,SO_SNDTIMEO,(char*)&timeout,sizeof(timeout));
if(bread == SOCKET_ERROR) {
fprintf(stderr,"failed to set send timeout: %d\n",WSAGetLastError());
ExitProcess(STATUS_FAILED);
}
然后在sendto和recvfrom出打印运行时间，如下：
bwrote = sendto(sockRaw,icmp_data,datasize,0,(struct sockaddr*)&dest,sizeof(dest));
printf("Send tick = %d\n",GetTickCount());
if (bwrote == SOCKET_ERROR){
if (WSAGetLastError() == WSAETIMEDOUT) {
printf("Request timed out.\n");
continue;
}
fprintf(stderr,"sendto failed: %d\n",WSAGetLastError());
ExitProcess(STATUS_FAILED);
}
if (bwrote < datasize ) {
fprintf(stdout,"Wrote %d bytes\n",bwrote);
}

printf("Middle tick = %d\n",GetTickCount());
bread = recvfrom(sockRaw,recvbuf,MAX_PACKET,0,(struct sockaddr*)&from,&fromlen);
printf("Recv timeout tick = %d\n",GetTickCount());
if (bread == SOCKET_ERROR){
if (WSAGetLastError() == WSAETIMEDOUT) {
printf("Request timed out.ms = %d\n",GetTickCount()-((IcmpHeader*)icmp_data)->timestamp);
continue;
}
fprintf(stderr,"recvfrom failed: %d\n",WSAGetLastError());
ExitProcess(STATUS_FAILED);
}

时间输出如下：
Send tick = 837359
Middle tick = 837359
Recv timeout tick = 837906
Request timed out.ms = 547

疑问是:为啥recvfrom不是在判断了20ms超时以后就打印信息，而是等了很长一段时间547-20ms以后，才执行下面的信息？难道recvfrom这个函数本身运行了500ms？

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