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Re: Options to replace select in Nsock
From: Brandon Enright <bmenrigh () ucsd edu>
Date: Sun, 21 Jun 2009 00:49:47 +0000

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On Sat, 20 Jun 2009 20:07:20 -0400
Michael Pattrick <mpattrick () rhinovirus org> wrote:

As a side note, the default limit of fd_set in windows is 64 according
to [0], Surprising that someone noticed an overflow on Linux before
Windows.

Considering Microsoft limited the number of pending connections to 10
until very recently it makes sense that it would be hard to get 64
sockets simultaneously open on Windows.  There is a pretty good
discussion of Winsock here:

http://tangentsoft.net/wskfaq/advanced.html


As for your code below, I think David is right in that it wont actually
work because although we'd be setting the bits for each file
descriptor, select() won't know to treat socket 1025 as socket 1025 and
not just socket 1.

Brandon



On Sat, Jun 20, 2009 at 7:28 PM, David Fifield<david () bamsoftware com>
wrote:
In the meantime, couldn't Nsock be quickly adapted to use multiple
calls to select with different FD_SET arrays when tracking >
FD_SETSIZE items?

I don't think you can use select that way. Each fd_set is indexed
starting at zero.

I was referring to something like this:

int numberOfSockets=2000;

fd_set *rfds;
struct timeval tv;
struct timeval dontStop;
int action = 0;
int i=0, k=0;
int selectorCount = ceil(numberOfSockets/FD_SETSIZE);

rfds = malloc(selectorCount);

for(i=0;i<selectorCount;i++){
 FD_ZERO(&rfds[i]);
}

for(i=0;i<numberOfSockets;i++){
 FD_SET(Socket[i], &rfds[floor(i/FD_SETSIZE)]);
}

/* Wait up to five seconds. */
tv.tv_sec = 5;
tv.tv_usec = 0;

dontStop.tv_sec = 0;
dontStop.tv_usec = 0;

while(1){
for(i=0;i<(selectorCount-1);i++){
 action = select(1, &rfds[i], NULL, NULL, &dontStop);
 if(action>0){
  actOnDescriptors(rfds[i])
  break;
 }
}
if(!action){
 action = select(1, &rfds[selectorCount-1], NULL, NULL, &tv);
 if(action){
  actOnDescriptors(rfds[selectorCount-1])
 }
}
}



[0] http://msdn.microsoft.com/en-us/library/ms740141.aspx

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