On Mon 20 Jun 2016 08:45, Chris Vine <ch...@cvine.freeserve.co.uk> writes:
> For simplicity, let's say you have a file watch in the glib event loop
> which has made a non-blocking read of the first byte of a multi-byte
> UTF-8 character, and the suspendable-ports implementation is in use
> because it is a non-blocking read of a TCP socket. (It could be
> something different: there may be a non-blocking read request for a
> complete line of text which has so far only partially been satisfied,
> but the partially complete character is the easiest example to deal
> with.) The read request is therefore in read-waiter waiting for a
> complete UTF-8 byte sequence to arrive. On the current hypothesis,
> read-waiter comprises a procedure which is suspended on a prompt
> waiting for an event to occur in the glib main loop which will cause
> it to resume, comprising the file descriptor becoming ready which will
> satisfy the read request. But while suspended in read-waiter, this
> prompt would have to service any user event sources which might become
> ready in the glib main loop, not just the particular file descriptor
> in question becoming ready.
I must not be communicating clearly because this is definitely not what
I am proposing. The prompt doesn't service anything, and it's just the
one user-space thread which is suspended, and when it suspends, it
suspends back to the main loop which runs as usual, timers and all.
prompt
/------\ /------------\|/-----------\ /------------\ /----------\
| main --> run-thread -|>(user code)--> read-char --> waiter |
| loop | | ||| | | | | |
\------/ \------------/|\-----------/ \------------/ \--|-------/
^ |
\-------------------------------/
stack grows this way ->
The current-read-waiter aborts to a prompt. That prompt is instated
when the thread is run or resumed. When you abort to that prompt, you
add the FD to the poll set / main loop / *, remember the delimited
continuation, and return to the main loop. When the fd becomes readable
or the gsource fires or whatever, you reinstate the delimited
continuation via a new invocation of run-thread (prompt and all).
> My approach on the other hand does not nest events from the glib main
> loop in this way.
"Nesting events" should not be a thing you have to do.
Andy
