Queues and Enumerated Types

[SercoSteveB]

What are the values of 'Queue Element Out' and 'Timed Out' following execution of the VI?

NOTE: The enumerated constant has four defined values Item 1, Item 2, Item 3 & Item 4.

a) Item 1, TRUE

b) Item 2, TRUE

c) Item 3, TRUE

d) Undefined (The VI does not complete)

[crossrulz]

The default value should be the first value in the enum.  So the answer would be A.

[Pratibha]

Ans:- A.

[Neelamma]

Ans:A

[drjdpowell]

It's (e) Unknown (because for all we know some other process has already obtained "StevesQueue" and enqueued an element before the 100 ms timeout).

Get rid of the queue name and the answer is (a).

[GayatriT]

Ans : A

[Asha_Nagaraj]

Ans : A

[SercoSteveB]

Good point drjdpowelland welcome to The Daily CLAD.  Accessing queues by name, from multiple processes, is an interesting subject.  Could you post what removing the queue name does for this VI?

I encourage you to answer based on the information in the question; fantasy processes are good for making a point but are a real problem when trying to create questions.

[drjdpowell]

The "name" on things like queues and notifiers is something that should almost always be left blank.  The name makes the queue globally accessible, and like any global it should be used only if necessary (and you should think twice to see if it really is necessary).  Without the name, I can trace the wire and tell where the queue is used; with the name, I have to search the entire application for other instances of the name.  With a name like "StevesQueue" it is even possible for another component in the application to accidentally use the same name (better to use "StevesQueue%3F4ru&" or some such randomized name).

In a real-world application, the code you show should only exist because some other process is accessing it through the queue name.

[crossrulz]

I think this should illustrate drjdpowell's point.  Now if the queues were not named, this issue would not exist.

[SercoSteveB]

Thanks drjdpowell & crossrulz.  I have always used queues (with names) to pass data between processes. 

We have a regimented design then development process here so we would never get in the situation where we are accidentally using a queue name over, but it is nice to be aware.

[santoshsss]

sir, can u explain me in detail about this concept, thank you

[crossrulz]

Which concept?  What part are you not understanding.

[debapriya_maji]

Is it that when the queue is empty, the deque function after time-out returns the default value?

[crossrulz]

debapriya_maji wrote:

                       

Is it that when the queue is empty, the deque function after time-out returns the default value?

                   

That is exactly what is happening here.