RE: iThreads troubles

On Wed, 19 Apr 2006, Daniel Rychlik wrote:

> Some of you have asked for code examples.
> 
> One of issues that I am having is when the thread enters into
> getAvailableResource routine its not seeing that the
> $Resources{'WAN1'}->{INUSE} = 1; has been made unavailable.  The idea is
> for the next thread to pick up the next unavailable resource.  I tried
> to sleep(1) between thread creation, and also used threads::shared
> share(%Resources); which also failed.  

Dan,

A few quick remarks/suggestions.

First, please post the smallest possible code that reproduces your symptoms:
pare down your problematic program, stuff it with stubs until you've got a
cogent proof-of-problem.

Second, &share()ing your hash clears it [0], so populate it /after/ you mark
it shared.  Additionally, the hash members themselves have to be explicitly
shared, IIUC. [1]

Third, your 'INUSE' check looks to have a race.  You'll need to &lock(), use
a semaphore, etc.  As others have suggested, Thread::Queue makes these kinds
of problems a lot easier.  You could, perhaps, manage the "wan" and "modem"
resources themselves in a queue -- pop off the next available one, use it,
then re-queue it for another job later on.  TMTOWTDI.

[0] "When share is used on arrays, hashes, array refs or hash refs, any
    data they contain will be lost."
    http://search.cpan.org/~jdhedden/threads-shared-1.01/shared.pm#BUGS_AND_LIMITATIONS

[1] "This places restrictions on what may be assigned to shared array and
    hash elements: only simple values or references to shared variables are
    allowed..."
    http://www.perldoc.com/perl5.8.4/pod/perlthrtut.html#Shared-And-Unshared-Data

Good luck,
Mike
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