Re: Question about an error with ports

[Chris Vine]

On Thu, 10 Mar 2022 18:46:34 -0500
Olivier Dion via General Guile related discussions <guile-user@gnu.org>
wrote:
> On Thu, 10 Mar 2022, Zelphir Kaltstahl <zelphirkaltstahl@posteo.de> wrote:
> 
> > Just one question: Why is get-bytevector-some better than
> > get-bytevector-n and specifying a number of bytes?
> 
> I haven't check the implementation details, but I think it's just a
> question of buffering.  `get-bytevector-n` will block just like
> `get-bytevector-some` when the port is empty.  The former will return up
> to N bytes and the latter might return more than N bytes.  The former
> probably also lead to less memory allocation since N is known in
> advanced, a singled allocation can be made, while the latter might do
> multiple allocations.  This can be useful depending on your usage of the
> port.  For example, you could make a web server that only accepts HTTP
> body up to 4096 bytes (1 system page).  This is what some web server
> does I think.
> 
> There's also `get-bytevector-all`, but this would lead to more memory
> usage and multiple allocations.  Again, it depends on the usage.

Avoid using get-bytevector-n!, get-bytevector-some and
get-bytevector-all if you are going to use something like fibers or
some other asynchronous i/o, as those procedures are not suspendable
(they can block).  get-bytevector-n (note the difference from
get-bytevector-n!) and get-string-all are suspendable and should
generally be preferred where suspension is required.