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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 other workarounds?

I don't have a simple example program but I can make one if that will help.



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