IBM Version 4 manual Using Data Queues versus, User, Queue entries are manipulated. F

Using Data Queues versus

User

Queues

Data queues and user queues both provide a means for one or more

communicate

asynchronously. The

queues

can be processed FIFO (first-in

first-out), LIFO (last-in first-out),

or

by

key. If user queues and

the same function, which one should

you

choose

for

your

implementatio

following is a comparison of the two

and

an

insight

into

when

you sho

queue rather than the other.

First, your programming experience is

an

important

consideration

in

sele

queue type. If you are skilled in

C or MI programming, you may want

user

queue. C

and

MI

are

the

only

languages

that

can

use MI instru

as discussed later, has a

bearing

on performance. If your expertis

RPG, then you should choose the data

queue. You

cannot

implement

a

u

queue in COBOL or RPG because neither of these languages can use M

instructions.

Next,

performance

plays

an

important

part

in determining what type of

use. As

stated

in

Chapter 1,

“Application

Programming

Interface—Overview”

page 1-1, APIs generally give better performance than CL commands. Also,

instructions perform better than an external

call

to

an API

because

head associated with them. User queues use

MI

instructions

to

manip

data queues use APIs. Therefore, the user

queue

has

better

perfo

data

queue.

Last,

you

need

to consider

how

the

queue entries are manipulated. F

you need a way to perform enqueue

and dequeue operations on entri

queue. As stated earlier, user queues use MI instructions to manipula

Specifically,

you

use

the

ENQ

MI

instruction

to

enqueue

a

message,

a

MI instruction to dequeue a message. If you are running at securit

greater,

you

must

ensure that the

user

queue is created in the u

to directly manipulate a user queue

using MI instructions. Because d

entries

are

manipulated

by

APIs,

the

security

level

of

the

machine

use

of

the

API.

You cannot create a user queue object in a library that does not domain objects, which is determined by the QALWUSRDMN system value. ( “Domain Concepts” on page 2-26 for more information on QALWUSRDMN.) Data queues are always created in the system domain, so there is no pr data queue being created into a specific library.

The	following			is	a	summary	to	help you	select the type of queue	t
your		program:
Ÿ	Use user			queues when:
	–	You	have		a	programming background			in or prefer to program in	C
	– You		need the additional					performance of an API for creating		an
		and	MI	instructions			for	manipulating	entries.

–You do not need to create a user-domain queue into a library QALWUSRDMN system value does not permit user-domain user objects

when	at	security level 40 or 50.
Ÿ Use data		queues when:
– You	have	a programming background in	or	prefer to program in COB
RPG.
		Appendix A. Performing	Tasks	Using APIs—ExamplesA-15