Monday, June 28, 2010

Quick Drop in LabVIEW 8.5

Even though Quick Drop was introduced in LabVIEW 8.6, there have been rumors on the internets that an 8.5 version existed. Those rumors are certainly true, since I prototyped Quick Drop well before LabVIEW 8.6 released.

I finally had some time to post my Quick Drop 8.5 prototype on the NI Community site. If you want Quick Drop functionality in LabVIEW 8.5, then download the prototype here:

Quick Drop in LabVIEW 8.5

Tuesday, June 8, 2010

I Like Global Variables

I think the title of this post alone will probably lose me some followers on this blog. :) Nevertheless, let's proceed...

Here's the deal...global variables are not evil. There are perfectly valid use cases in which a global variable is the best tool for the job, and doing something more complicated just to say, "I didn't use globals!" doesn't make sense. Now sure, globals can be abused, and there are certainly scenarios where they are contraindicated. But if you're aware of those situations, and you avoid them, you should feel free to use globals where needed. So let's look at some use cases where, in my opinion, globals can come in handy:
  • Static Data - Whenever I create a UI in LabVIEW in which user-visible strings are programmatically changed, I always store those user-visible strings in a global variable. Let's call this kind of global a Write Never, Read Many (WNRM) global. I am never writing new values into this global...I'm only reading from it in my code whenever I need to update a user-visible string. Another use case for WNRM globals is in scripting apps. When I'm doing code generation involving templates, I always store the identifying labels of panel/diagram objects within a global, and I always read those identifiers from a global in my scripting code. That way, if I need to change the identifiers in the templates, I know that I'll only need to change the identifier in one place (my global) in my scripting code. (Note: I believe Yair's Adding CONSTs to LabVIEW idea on the Idea Exchange is intended to facilitate a cleaner implementation of this use case.)
  • Debug Flags - If I've got parts of my code that I want to run differently when I'm debugging, I use a WNRM global. I'll open the global and change the debug flags before I run my code. Someone once suggested that I should instead use Conditional Disable Structures with conditional symbols in my project, but after I looked into it, I decided that the added complexity and configuration associated with conditional symbols didn't add enough value over the simple global solution.
  • Configuration Data - In this scenario, we are initializing configuration data (from an INI file, for instance) at some point in our code, and reading that data at later points. So here we have a Write Once, Read Many (WORM) global. (Note: The term WORM global was first coined by tbob on the NI Forums a few months back.) As long as there is one, single place where the global is written, it is perfectly fine to have many other places in your code that read that global.
Now one of the biggest reasons given as to why globals should be avoided is that new users could easily find themselves in race conditions if they're not careful. But with the use cases above, there should never be any worry about race conditions, as long as developers adhere to the WNRM/WORM constraints. I don't think we should hamstring ourselves with a blanket refusal to use a feature when it really can be a performant time-saver when utilized correctly.