On 4/22/2015 8:12 PM, David Vanderson wrote:
On 04/20/2015 05:54 AM, George Neuner wrote:
I know I need a different response function. The question was
whether embed/url is tied to HTML or can be used in a different
context. The documentation (6.1.1) says:
"When used inside page
<mailbox:///C:/Users/GW/Documents/Eudora/local/Mail/Local%20Folders/Drafts?number=0&part=1.2.2&filename=page.html>
syntactically, a rename transformer for the procedure embedding
function; otherwise, a syntax error."
That suggests embed/url can be used only in (X)HTML responses and
that I need to use something else to create dispatch URLs in regular
code.
I think I see why that's confusing. The syntax parameter "embed/url",
is not being used in the code I sent. In that code, "embed/url" is
the name of a regular parameter to the lambda function being supplied
to send/suspend/dispatch. I probably should have used a different
parameter name. Does that make sense?
Ok. I guess then an example would be helpful: how to generate 2
continuation URLs in Scheme code and stick them into a hash.
My code now looks like:
create a hash representing the return object
- data to return
convert the hash to a jsexpr
send/back the jsexpr
What I want to do is:
create a hash representing the return object
- data to return
- URL for next page function (if applicable)
- URL for prev page function (if applicable)
convert the hash to a jsexpr
send/suspend/dispatch the jsexpr
My understanding is that when you do send/suspend*, the continuation
is saved, and the thread finishes. The continuation and thread are
not bound together. So when a request comes in to continue that
continuation, it will be a different (new?) thread that runs it.
That's fine: the "term" thread is overloaded. I understand that Racket
threads are user-land scheduler activations [I think that's the term]
... i.e. just multiplexed continuations. My point was that there is
some execution context hanging around when the "thread" is suspended and
it wasn't clear that it would be GC'd if/when all the thread's
send/suspend "continuations" expire.
There's nothing that says definitively that the servlet continuation
manager is holding the *only* references to the thread context [or the
only strong references if that's more applicable] - somewhere I recall
Jay explaining the structure being something like:
server->custodian->custodian(s)->thread(s)->user-stuff ???
and it is not clear where the continuation manager lives in the
hierarchy [ though I can guess ].
Can you give an example of the processing that you want to know has
been finished? Do you want the thread serving the request to do some
processing after sending the response?
The thread can be suspended after sending a response. What I'd like,
though, is for it to wake up again and log some exit data when all
continuations expire.
That could - with difficulty - be done from an exception handler if the
thread is terminated by exception as opposed to simply evaporating, and
also provided that I know what exception(s) to catch or events to wait
on. One of the issues I've had with real-world Racket programming is
determining what exactly happens when things go wrong. A catch-all exn
or exn:fail handler doesn't cut it when you need more detail, and, of
course, the hierarchy is extensible so things may be thrown that aren't
documented. "read the code" is fine for research, but it isn't a
realistic real-world answer - there's too much code and not enough
time. As I said to Jay recently, I wouldn't know where to look even if
I had the source.
Thanks,
Dave
Thank you,
George
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