Darren's Weekly Nugget 10/02/2006

[chilly_charly]

Joyeux Anniversaire Darren !

[Ben]

Adding to Darren's wish list...

I would like to see a new test added to the VIA that looked for multiple writers of Locals and Globals. More thatn one writer gives a warning.

In the distant future I'd like LV to help enforce the single writer idea by allowing only one writer of of a global by default. Attempts to change to write would give a similar warning and remind the developer where the other writing of the globla is happening.

Ben

[TiTou]

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Ben a écrit:

In the distant future I'd like LV to help enforce the single writer idea by allowing only one writer of of a global by default. Attempts to change to write would give a similar warning and remind the developer where the other writing of the globla is happening.

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... and LV offers to automatically replace all the instance of the global with a FGV

[tst]

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@TiTou wrote:

... and LV offers to automatically replace all the instance of the global with a FGV

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But an FGV is not inherently any less prone to race conditions than a global. You have to add locking to it or place the functionality inside it to prevent race conditions. It does give better memory performance at the price of speed. I really wish that people would stop automatically thinking of FGVs as the automatic solution to all the world's problems.

And yes, I remember that I didn't finish with the globals thread in the BP. Shame on me...

[TiTou]

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tst a écrit:

But an FGV is not inherently any less prone to race conditions than a global. You have to add locking to it or place the functionality inside it to prevent race conditions. It does give better memory performance at the price of speed. I really wish that people would stop automatically thinking of FGVs as the automatic solution to all the world's problems.

And yes, I remember that I didn't finish with the globals thread in the BP. Shame on me...

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Right tst, nothing is perfect and we should use the most appropriate technique. Yes, many people, including myself, automatically think of FGV which is not always appropriate. Who's perfect ?

Anyway, having a built-in function in LabVIEW to "control" that the developper is not making a "bad" use of globals would be nice, no ?
Offering to replace by something else... well I am among the firsts who hate "things that know better than you what you want to do", so it was more a joke than a wish.

Don't feel ashamed about  the global thread in BP, you did very well to raise this point and started to do a good job... and none of us jumped in to give you a hand. Shame on us ! 😉

[K1200LT_rider]

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But an FGV is not inherently any less prone to race conditions than a global. You have to add locking to it or place the functionality inside it to prevent race conditions. It does give better memory performance at the price of speed. I really wish that people would stop automatically thinking of FGVs as the automatic solution to all the world's problems.

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Exactly the conclusion I came up with when I was trying to fix a pre-existing, large application of ours with a multitude of race conditions all over the place.  That was definitely a buggy test station app when I started on it.  It has 6 parallel loops in the main block diagram if that gives you any idea for the race condition potential.  It would intermittently hang and do a handful of other weird things, so the operator of the station definitely wasn't happy.  Talk about getting thrown into a major coding situation cold turkey (as a freshly certified CLAD).  I finally got the majority of the race conditions taken care of by simply changing things around so there was only 1 writer for each global.

- Brad

[Ben]

Darren asked

"

A block diagram comment should word-wrap if it's being typed inside a structure, and the comment bound approaches the edge of the structure.  Actually, it would be nice if a comment typed anywhere on the diagram would word-wrap if its bound approaches any diagram object.

"

Well this is ont exactly what you wished for but its close!

Aristos Queue posted in post #102 of this thred on the LV site

http://forums.lavag.org/index.php?showtopic=1576&pid=17521&st=90&#entry17521

The following

"

But... from LV7.0 forward...
After you drop the string control, type for a while. When the string reaches the max width that you want, hit shift+Enter. Keep typing. The string will now wordwrap at the current width, and grow vertically. When you reach the maximum desired height, hit shift+Enter again. The vertical scrollbar will appear and the string will now scroll instead of growing any further.

Sorry... the trick doesn't work on free labels. Perhaps someday...

"

I just verified this for a LV 7.1 string constant on the diagram.

So can we check-off one of your wish-list items?

Ben

[tst]

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@Ben wrote:

"...Sorry... the trick doesn't work on free labels. Perhaps someday..."

...

So can we check-off one of your wish-list items?

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I would say no. To use a comment when the auto tool is on, all you need to do is double click the diagram and start typing. To use a string you need to find the string constant on the palette. Therefore, this would only really be useful when it is available for comments as well.

[Ben]

Hi tst,

You bring up an intersting point.

I went to the VI Checklist

http://zone.ni.com/reference/en-XX/help/371361A-01/lvdevconcepts/checklist/

to try to find the note that said that if you are entring a lot of comments, that it is recomended that you use a string constant with the scroll bar showing. Well it appears that note has been deleted. So what used to be good is now bad. I would not care about that kind of hair splitting if I didn't have to pass a test every couple of years.

Ben

[Will.D]

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@Ben wrote:
After you drop the string control, type for a while. When the string reaches the max width that you want, hit shift+Enter. Keep typing. The string will now wordwrap at the current width, and grow vertically. When you reach the maximum desired height, hit shift+Enter again. The vertical scrollbar will appear and the string will now scroll instead of growing any further.

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Ben, this is a nugget in its own right!  The number of times this could've saved me considerable frustration...

Very handy to know.  Thanks for posting it!