[plt-scheme] no #!eof

From: Neil Van Dyke (neil at neilvandyke.org)
Date: Wed Apr 16 02:19:13 EDT 2008

Matthew Flatt wrote at 04/15/2008 07:51 AM:
> At Tue, 15 Apr 2008 03:38:07 -0400, Neil Van Dyke wrote:
>> Incidentally, in some experimenting just now, it seems the "sync" of PLT 
>> 372 and has the expected blocking behavior on a FIFO up until 
>> the first EOF, but subsequently does not block on the FIFO.  If multiple 
>> input segments are supported, should this EOF behavior in "sync" be changed?
> I'm not suite sure what you mean. Can you provide an example?
If I do these three things:

1. Shell command: mkfifo /tmp/my-fifo

2. Start this in MzScheme 372:

(let ((in (open-input-file "/tmp/my-fifo")))
  (let loop ()
    (sync in)
    (printf "hit ~S\n" (read-byte in))

3. Shell command: echo 123 > /tmp/my-fifo

Then the output from the MzScheme process will be:

hit 49
hit 50
hit 51
hit 10
hit #<eof>
hit #<eof>
hit #<eof>
hit #<eof>
hit #<eof>
hit #<eof>

Given the discussion yesterday, I'd expect "sync" to block after 
printing the first "hit #<eof>", until I wrote more input to the FIFO, 
but it no longer blocks after the first EOF.

I also see the same behavior when using "cat" to write incrementally to 
the FIFO -- "sync" blocks as expected, until "cat" exits, then "sync" no 
longer blocks.

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