On 6/16/2021 3:45 PM, Matthew Flatt wrote:
At Wed, 16 Jun 2021 14:25:40 -0400, George Neuner wrote:
> It looks like the problem
> is that "flush" is not defined ...
Yes, "returns without blocking after writing as many bytes as it can
immediately flush" is vague, and more or less intentionally so. The
intent it really "writes as much as is convenient, with the guarantee
that anything written is completely flushed". Maybe the documentation
should be revised to say something more like that.
There's not intended to be a guarantee that as much is written as could
possibly make sense by `write-bytes-avail`. Implementation issues may
make writing additional bytes inconvenient enough that it doesn't
happen, for example, even if more is always written on the next
`write-bytes-avail*` call. Also, ports are meant to be used in
concurrent settings where the notion "as much as possible" is prone to
race conditions.
Dumb question ... why should non-blocking I/O worry about "flush" at
all. Why not behave like native I/O where writes are guaranteed only to
get to the I/O buffer?
The Racket BC and CS pipe implementations find different things
convenient, in this sense, and that's why they behave differently in
the example. (That is, it's not really about the Racket version, but CS
versus BC.)
So, the intent is that you use `write-bytes` when you want to wait
until all bytes are written (maybe because you know that will be soon
enough, for whatever reason). But when using `write-bytes-avail`, be
prepared for a fraction of the bytes to be written, for whatever
reason.
It is not a problem, per se, but it is an issue that with a long string,
you may be forced to call write-bytes-avail multiple times just to be
filling up the port buffer. That seems very inefficient and is at odds
with how native non-blocking I/O calls behave (completing or filling the
buffer before returning).
YMMV,
George
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