User`s guide

5 Acquiring Image Data

5-30

Using Critical Sections

This section describes how to use critical sections to protect portions of your adaptor code.

The section describes the adaptor kit's main critical section class, ICriticalSection,

and the ancillary class, IAutoCriticalSection, that you use to manage critical

sections. Topics covered include

• “Understanding Critical Sections” on page 5-30

• “Example: Using a Critical Section” on page 5-31

Understanding Critical Sections

To prevent sections of code or resources from being accessed simultaneously by multiple

threads, use critical section (ICriticalSecton) objects. The basic process for using a

critical section has three-steps:

Create a critical section object, using the adaptor kit createCriticalSection()

function.

At the point in your code that you want to protect, enter the critical section by calling

the ICriticalSection::enter() member function.

At the end of the code that you want to protect, leave the critical section by calling

the ICriticalSection::leave() member function.

While this process might appear simple, using a ICriticalSection object directly

in this way can expose your adaptor to problems. For example, if an error occurs in the

protected code, the call to the leave() function might never be executed. Entering a

critical section and then never leaving it can cause unexpected results.

To make working with critical sections easier, the adaptor kit provides a second class,

called IAutoCriticalSection, that can help you manage the critical sections you

define.

You first create an ICriticalSection object and then pass this object

to the createAutoCriticalSection() function when you create the

IAutoCriticalSection object. When you create the object, you automatically enter

the critical section without having to call the enter() function. When the protected

code goes out of scope, the auto critical section automatically leaves the critical section

without your code having to call the leave() function.