select（）之后的FD_ISSET（）未检测到接收到的数据
我有一个程序，我设计在一堆不同的节点上运行，根据它们从主节点上运行的进程中得到的指令在它们之间传输文件。每个进程同时充当发送方和接收方 我的策略是：select（）之后的FD_ISSET（）未检测到接收到的数据,c,linux,sockets,C,Linux,Sockets,我有一个程序，我设计在一堆不同的节点上运行，根据它们从主节点上运行的进程中得到的指令在它们之间传输文件。每个进程同时充当发送方和接收方 我的策略是： //Setup a listener socket on port 63000(say) to listen to commands from the master //socket. This listener will only listen for commands and read these commands /* 1) Set
//Setup a listener socket on port 63000(say) to listen to commands from the master
//socket. This listener will only listen for commands and read these commands
/* 1) Setup a listener socket on port 63001(say) to listen to connection requests from
(NUMNODES-1) other processes on the rest of the nodes
2) Accept each of the connections from the rest of the (NUMNODES-1) nodes and fill
these conneced descriptors into an array of integers */
for(i=1;i<NUMNODES;i++){
connfd=accept(...,&node_addr,...);
index=findNodeIndex(node_addr); //To find the node number, corresp to this address
connections[index]=connfd;
}
/* Skipping all details aside, assuming i have a process running on node number 4 (out
of a total of 10 nodes, say) connections[4] will be -1, and connections[1..3, 5..10]
will hold connection descriptors to each of the other nodes, ready to read any file
that they decide to transfer */
fd_set read_set;
for(i=1;i<=NUMNODES;i++){
if(i==thisNodeNum()) //For nodenum 4, the connections[4] will be -1
continue; //So we don't want to put it into the read fd_set
FD_SET(connections[i],&read_set);
}
fd_set temp_rset;
//A select() call ready to listen to any data that comes in from any of the nodes
for(;;){
temp_rset=read_set;
select(maxfdp1,&temp_rset,NULL,NULL,NULL);
//Listening for commands from master goes here
if(FD_ISSET(commandListener,&temp_rset){
... listen to command and send file to a particular node...
... File will be sent to port 63001 on that node...
... commandLIstener listens for commands on port 63000(just a reminder)...
}
//Listening for data that has come in from the other nodes
for(i=1;i<=NUMNODES;i++){
if(FD_ISSET(connections[i],&temp_rset){
... write file to the local hard disk, byte by byte...
}
}//End of connections[1..NUMNODES] testing for data to read
}//End of infinite for loop
我做错了什么 您的代码应该如下所示：
fd_set read_set; // set of file descriptors (in this case sockets)
int result;
for(;;)
{
FD_ZERO(&read_set); // you need to clear the set first!
FD_SET(commandListener, &read_set); // add command socket to the set
for(i=1; i<=NUMNODES; i++) // add node sockets to the set
{
if(i==thisNodeNum()) continue;
FD_SET(connections[i], &read_set);
}
// check status of all sockets from the set
result = select(maxfdp1, &read_set, NULL, NULL, NULL); // instead of tracking maxfdp1 you can use FD_SETSIZE (maximum allowed size of set)
if(result == -1) // error
{
perror("select() error");
}
else if(result > 0) // there is new data
{
if(FD_ISSET(commandListener, &read_set) // there is new command data
{
// (...) handling your tasks here
}
for(i=1; i<=NUMNODES; i++)
{
if(FD_ISSET(connections[i], &read_set) // there is new data on i-th node
{
// (...) handling your tasks here
}
}
}
}//End of infinite for loop
您的accept循环接受来自NUMNODES-1其他节点的连接。因此，如果所有节点都运行此代码，这意味着所有节点都必须连接到其他节点。这意味着您将在每对节点之间建立两个连接，从每个方向启动一个连接
现在，当您为select循环设置read_set时，看起来您只查看已接受的连接，而不是调用connect的连接。如果您同时在已接受的连接而不是已连接的连接上发送数据，则另一端的进程不会注意到它，因为它正在等待其已接受的连接而不是已连接的连接。您必须在每次调用之前重新设置fd_集，以便在循环中进行选择-请参阅@ChrisStratton:OP的代码就是这样做的。参见：临时设置=读取设置；对不起，我错过了。如果能弄清楚select是否返回，如果是的话，找出它在没有提供超时的情况下返回的原因，也许会有帮助。返回值是多少？是否表示应检查errno？对于i=1；i> fori=0；i