This chapter discusses using multithreading to improve LabVIEW applications’
performance. Multithreading is an advanced programming topic, and its use requires
the programmer to posses a fundamental understanding of this technology. Lab-
VIEW provides two significant advantages to the programmer when working with
multitasking and multithreading. The first advantage is the complete abstraction of
the threads themselves. LabVIEW programmers never create, destroy, or synchronize
threads. The second advantage is the dataflow model used by LabVIEW. This model
provides G a distinct advantage over its textual language counterparts because it
simplifies a programmer’s perception of multitasking. The fundamental concept of
multitasking can be difficult to grasp with text-based languages.
Multithreading adds a new dimension to software engineering. Applications can
perform multiple tasks somewhat simultaneously. A good example of an application
that has added multithreading is Microsoft Word for Windows 95 (Version 7.0).
Word for Windows 95 uses multithreading to perform spell-checking and grammar
validation. The threads added to perform this task allow the application to perform
these tasks while the user is typing. The previous version, Word 6.0 for Windows
3.1, cannot do this because it runs only one task at a time; a user would have to
stop typing and select
Check Spelling
. The first six sections of this chapter provide
the basic knowledge of multithreading. This discussion focuses on definitions, multitasking
mechanics, multithreading specific problems, and information on various
thread-capable operating systems.
A brief section on multithreading myths is presented. The impact of multithreading
on applications is misunderstood by a number of programmers. Section 9.6
explains precisely what the benefits of multithreading are. Many readers will be
surprised to learn that multithreading does little to increase the speed of an application.
Multi-threading does provide the illusion that sections of an application run
faster.
The last three sections of this chapter are devoted to the effective use of multithreading
in LabVIEW. A strategy to estimate the maximum number of useful threads
will be presented. The focal point of this chapter is using subroutine VIs to maximize
application performance. The use of threads adds a new dimension of benefits to
both subroutine VIs and DLLs.