| Re: global singleton object ? [message #26874] |
Wed, 03 October 2001 09:59  |
R.G.S.
Messages: 46
Registered: September 2000
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Member |
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Pavel A. Romashkin <pavel.romashkin@noaa.gov> wrote in message
news:3BBB2D52.346B882B@noaa.gov...
> Bob,
>
> The following URL points to a tiny file that does what you want.
> http://spot.colorado.edu/~romashki/idl/sobj_new.sav
> The SOBJ_NEW does not call OBJ_NEW is a singleton object already exists,
> thus avoiding OBJ_NEW overhead.
> I also recommend checking out
> http://spot.colorado.edu/~romashki/idl/single_set.sav
> which provides essentially the same services except the contents can be
> of any type, not just object. SINGLE_SET does not loop through heap
> variables, fetching the only one (the named one) of interest.
> The actual code is too embarassing to share, JD would not let me on the
> newsgroup again :-(
>
> s = sobj_new(/help) ; How to use it
> s = sobj_new() ; Make new object
> d = sobj_new() ; Get a reference to it again
> help, s, d ; Make sure they are the same
> ; Set NO_KILL to see what it does
> s -> store, obj_new('IDLgrModel'), /no_kill
> s -> store ; Take a look at contents...
> d -> store ; They are the same
> obj_destroy, s ; And kill it (by accident).
> d = sobj_new() ; NO_KILL was set, so it did not die.
> ; But NO_KILL is NOT set in D now, so that heap-gc, if
> ; ever used, does not go into an infinite loop.
> d -> store ; Make sure contents are the same
> ; except for NO_KILL setting. Set it again if you want.
>
> Cheers,
> Pavel
>
> P.S. The only use for a Singleton (or SINGLE_SET) that I can see is
> avoiding Common blocks while
> still allowing sharing some information between widget programs that may
or
> may not be launched independently, without using linking arguments. Or, as
> people asked before, keeping a Preferences structure for the duration of a
> session. When I wrote Display routines, I had to use Common block to keep
> track of linked displays and the topmost one because they were intended to
> be used interactively, and there is no way to define how many of them are
> present and in which order. A singleton would allow this without a common
> block.
Thanks for the reply!
As for why a singleton is useful, just wait til IDL is multithreaded. When
you
have multiple processes that need acces to information (info that can be
changed by the user) then a singleton object is very nice! Very Very Nice.
Cheers,
bob stockwell
PS BUFFY LIVES!
ack, geek cover blown, get out of that newsgroup now!
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