[Glass] Printer spooler and TransientSemaphore wait

[James Foster via Glass]

Dario,

Are you intending the semaphore to work between gems? If so, then it won’t work. A semaphore is “DbTransient,” meaning that its state is not persistent in the database. A Smalltalk Semaphore works only inside a single virtual machine (Gem).

Instead, it should be sufficient for you to use GemStone’s transaction semantics. A “producer” adds and item to an RcQueue and commits, while a “consumer” periodically aborts and looks to see if the queue is non-empty. For simplicity, the consumer should have a delay in its polling loop.

James

> On Jul 10, 2018, at 8:17 AM, dario.trussardi at tiscali.it via Glass <glass at lists.gemtalksystems.com> wrote:
> 
> Ciao,
> 
>     in the application based on Seaside, i manage some printers devices.
> 
> 	Every device have a RcQueue where the system add the 'works' to print. 
> 
> 	Besides there is a topaz script/server, which read the prints jobs and does the printing.
> 
>     Now this script is based spoolSemaphore class variable set to on TransientSemaphore, 
>         who waits for the presence of a new document to be reported,
> 
> 	segnaled when one relative entry is added to one RcQueue printer device.
> 
> 
> 
> 	This is the printerSpool script:
> 
>   startPrinterSpool
>   | cllDbSpoolerActive flagLo......................  |
> 
>   UserGlobals at: #'FlagSpooler' put: true.
> 
>   spoolSemaphore := TransientSemaphore new.
>  
> 
>      [ UserGlobals at: #'FlagSpooler' ]
>         whileTrue: [ 
>               spoolSemaphore  waitForSeconds: 1.
>               
>             System commit. " Update the session data "
>             counterLimit := DTRdbOperatingDevice ticktesForCicle.
> 
>             ....................
> 
>             .............
>          If in the whileTrue loop i define the:
> 
>               spoolSemaphore  waitForSeconds: 1.
> 
>         the topaz script works, but not waiting  as I would like .....
> 
> 	If in the whileTrue loop i define the:
> 
>               spoolSemaphore  wait.
> 
>         the topaz script generates the error:
> 
> 	ERROR 2366 , a ThreadError occurred (error 2366), reason:rtErrSchedulerDeadlocked, The ProcessorScheduler is deadlocked (ThreadError)
> 
>  
> 	Considerations... ?
> 
> 	Thanks,
> 
> 		Dario
> 
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