On Fri, 10 Jan 2014, dsl101 wrote:
Hi Ron,
Thanks for that - but I can only see #dataAvailable for Sockets, not for
FileStream (named pipes). I think the same kind of thing is available for pipes
(you can do `pipe size` to see how much data is there),
but it still doesn't wait. I'm trying to avoid a busy loop waiting for the data
- like this:
FileStreams don't have semaphores, so you can only use busy waiting with
them. However there's AsyncFile, which can do what you want. But its
interface is a bit cumbersome, and it's hardly tested/used at all. Here's
how it could work:
| syncSemaphore file message |
syncSemaphore := Semaphore new.
file := AsyncFile new.
file open: 'your_pipe' forWrite: true.
message := 'Here''s Johnny!!!!'.
file writeBuffer: message atFilePosition: 0 onCompletionDo: [
syncSemaphore signal ].
(syncSemaphore waitTimeoutMSecs: 3000) ifTrue: [
"handle timeout" ].
file readByteCount: 32 fromFilePosition: 0 onCompletionDo: [ :response |
message := response.
syncSemaphore signal ].
(syncSemaphore waitTimeoutMSecs: 3000) ifTrue: [
"handle timeout" ].
Transcript show: 'Received: ', message; cr.
file close.
Using syncSemaphore is a must, because the callbacks are evaluated from
another process.
Levente
P.S.: If you want to communicate with another program from Squeak, then
you should use Sockets if possible, since those are versatile and well
tested.
start := DateAndTime millisecondClockValue.
(pipe size < 32) & (DateAndTime millisecondClockValue - start < 3000) ifTrue: [
(Delay forMilliseconds 50) wait.
]
pipe size = 32 ifTrue: [
"Get data"
] ifFalse: [
"Deal with timeout"
]
The shorter the 'wait', the more responsive the code is to data arriving on the
pipe, but the more CPU it will use as it spins round the loop. The longer the
'wait', the more lag it has for data coming back.
That's what I'm trying to avoid by blocking on the read, but with a way to
escape after some timeout.
I'm guessing the call to 'pipe next:' is a primitive, and blocks there, which
is why valueWithin:onTimeout: doesn't return after the timeout, but does
eventually return the correct answer. So, I'm guessing
I'll have to do something like this:
* Set up a semaphore
* Fork the blocking read process, which will signal the semaphore if it ever
returns its 32 bytes
* In the main thread, wait for up to 3 seconds for the semaphore to be
signalled
* If the semaphore times out, kill the forked process
Obviously there's a potential race at the end there, but the worst case is we
throw away data which was returned at the last moment. Is there anything else
you can see wrong with this approach?
Thanks,
Dave
On Thu, Jan 9, 2014 at 9:16 PM, Ron Teitelbaum [via Smalltalk] <[hidden email]>
wrote:
Hi Dave,
See #dataAvailable ??and #recieveAvailableData.
It's never good to call for data if you don't know you have any. ??Better
to
setup a wait for data until call instead. ??
All the best,
Ron Teitelbaum
Head Of Engineering
3d Immersive Collaboration Consulting
[hidden email]
Follow Me On Twitter: @RonTeitelbaum
www.3dicc.com
https://www.google.com/+3dicc
> -----Original Message-----
> From: [hidden email] [mailto:[hidden email]
> [hidden email]] On Behalf Of dsl101
> Sent: Thursday, January 09, 2014 10:16 AM
> To: [hidden email]
> Subject: [Newbies] Read a filestream (named pipe) with a timeout
>
> I'm using Squeak 4.2 and working on the smalltalk end of a named pipe
> connection, which sends a message to the named pipe server with:
>
> msg := 'Here''s Johnny!!!!'.
> pipe nextPutAll: msg; flush.
>
> It should then receive an acknowledgement, which will be a 32-byte md5
hash of
> the received message (which the smalltalk app can then verify). It's
possible the
> named pipe server may have gone away or otherwise been unable to deal with
> the request, and so I'd like to set a timeout on reading the
acknowledgement.
> I've tried using this:
>
> ack := [ pipe next: 32 ] valueWithin: (Duration seconds: 3)
onTimeout: [
> 'timeout'. ].
>
> and then made the pipe server pause artificially to test the code. But the
> smalltalk thread blocks on the read and doesn't carry on (even after the
> timeout), although if I then get the pipe server to send the correct
response
> (after a 5 second delay, for example), the value of 'ack' is 'timeout'.
Obviously
> the timeout did what it's supposed to do, but couldn't 'unblock' the
blocking
> read on the pipe.
>
> Is there a way to accomplish this even with a blocking FileStream read?
I'd rather
> avoid a busy wait on there being 32 characters available if at all
possible.
>
> Thanks,
>
> Dave
>
>
>
> --
> View this message in context:
http://forum.world.st/Read-a-filestream-named-
> pipe-with-a-timeout-tp4735456.html
> Sent from the Squeak - Beginners mailing list archive at Nabble.com.
> _______________________________________________
> Beginners mailing list
> [hidden email]
> http://lists.squeakfoundation.org/mailman/listinfo/beginners
_______________________________________________
Beginners mailing list
[hidden email]
http://lists.squeakfoundation.org/mailman/listinfo/beginners
________________________________________________________________________________________________________________________________________________________________________________________________________________
If you reply to this email, your message will be added to the discussion below:
http://forum.world.st/Read-a-filestream-named-pipe-with-a-timeout-tp4735456p4735547.html
To unsubscribe from Read a filestream (named pipe) with a timeout, click here.
NAML
________________________________________________________________________________________________________________________________________________________________________________________________________________
View this message in context: Re: Read a filestream (named pipe) with a timeout
Sent from the Squeak - Beginners mailing list archive at Nabble.com.
_______________________________________________
Beginners mailing list
Beginners@lists.squeakfoundation.org
http://lists.squeakfoundation.org/mailman/listinfo/beginners
