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VM and non-blocking writes
- From: Wayne Christopher <wayne at 4raccoons dot com>
- To: cygwin at cygwin dot com
- Date: Thu, 13 Dec 2007 09:34:41 -0800
- Subject: VM and non-blocking writes
I have a server application that runs on XP under the latest cygwin,
that opens up a socket connection to a client on another system, makes
that socket non-blocking using fcntl(.... O_NDELAY), and then feeds the
client a large file (100's of MBs) by doing the following:
1. call write() with the entire size of the data not yet written
2. the return value of write is the number of bytes actually written
(should be limited by the socket buffer size - it is on linux)
3. select() for writable status on the socket (and do other things in
the mean time)
4. when the socket becomes writable, goto 1
What I see is that no matter how large the size is that I give to
write(), the return value is always the full size. Also, I see the
virtual memory used by my process go way up - in fact it goes up by much
more than the amount of data I've written.
I tried putting in a limit of 10KB in the size given to the write()
call. I still see the VM size grow - more slowly this time, but it
eventually reaches 1.5GB and then I'm out of memory.
Has anybody seen this behavior? Should I not be using O_NDELAY? Any
I don't have a simple example program but I can make one if that will help.
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