process_send_string blocks?

[Stephen Leake]

I'm trying to use a background process to parse buffer text, and send
results back to Emacs.

For large buffers, Emacs hangs; only killing the background process
externally recovers. This does not happen for small buffers (< 5k bytes?).

It appears that process-send-string is blocked on a full IO send queue,
while the background process is also blocked on a full IO send queue.

On reading process.c, I believe this should not happen, if the OS supports
EWOULDBLOCK. 

Is that true, even when there is only one call to process-send-string that
sends the entire buffer?

The doc string for process-send-string says "if > 500 chars, string is
sent in bunches", but I see no evidence of that in process.c. Is that
refering to the OS IO queue buffer size?

I'm running on Windows 7, using the Windows binary
emacs-23.4-bin-i386.zip from the FSF FTP site.

Is EWOULDBLOCK supported on this system?

I'll try compiling Emacs from source so I can run the debugger; I've
never tried that on Windows before.

I'd hate to have to code the partial read/partial write logic at the
elisp level.

-- 
-- Stephe