On Mar 18, 2006, at 4:18, Leopold Toetsch wrote:
On Mar 18, 2006, at 5:05, Allison Randal wrote:
+=head3 Hybrid solution
+
+Another option is to return a status object from each I/O
operation.
I'm in favour of such a solution.
Also my favorite.
+The disadvantage is that a status object involves more overhead
than a
+simple integer status code.
Well, IO goes usually through several layers aka function calls,
and isn't one of the fast operations a computer performs. And:
- int status codes (if checked) are usually just converted to PMCs
by HLL compilers
- if PMC creation becomes a bottleneck, then we should fix it and
not avoid or work around it
I had to list *some* kind of disadvantage, or it would sound too good
to be true. ;)
Seriously, though, it's important to consider all the advantages and
disadvantages, even if we decide the advantages outweigh the
disadvantages (as is the case here).
That said I can imagine to unify sync/async at the surface. E.g.
sync operation:
PResult = Pio."read"(n) # PResult = String/IOError object
async operation:
PAsync = new .IOAsync, Pcallback
PAsync."set_callback"(Pcb) # or method
...
Pio."async"(PAsync)
PStatus = Pio."read"(n)
Both the sync and async read bubble down the layers until one is
found that supports the operation either directly or by e.g.
emulating async. But due to the same function call signature, we
can avoid duplication of code paths.
That interface is unnecessarily complex. But more importantly, the
choice between async and sync is not set per filehandle, it's per
operation. It could be very common to combine the two, such as using
synchronous operations for opening and closing a filehandle, and only
using asynchronous operations for the heavy lifting of slurping in an
entire file.
But, yes, I agree with the principle of not maintaining two
completely separate implementations for synchronous and asynchronous
ops. The earlier design approached that by having the synchronous ops
be asynchronous internally, but my draft suggests this be handled by
having the asynchronous ops use the synchronous ops internally.
Allison
