User`s guide

Using Critical Sections

5-31

The auto critical section object ensures that you always exit a critical section. However,

you must also ensure that the auto critical section itself gets deleted. To do this,

the adaptor kit recommends managing the handle to the IAutoCriticalSection

object, returned by createAutoCriticalSection(), as an auto_ptr using the

std::auto_ptr<> template class from the Standard Template Library. The auto_ptr

helps ensure that the IAutoCriticalSection handle is deleted.

Example: Using a Critical Section

To define a section of code as a critical section, follow this procedure.

Create an ICriticalSection object, using the createCriticalSection()

function. Adaptors typically create an ICriticalSection object in their

constructors — see “Implementing Your Adaptor Class Constructor” on page 4-12.

_mySection = imaqkit::createCriticalSection();

The function returns a handle to an ICriticalSection object. _mySection, which

is declared as a member variable in the adaptor class header file, as follows.

imaqkit::ICriticalSection* _mySection;

At the point in your code that you want to protect, create an

IAutoCriticalSection object. The IAutoCriticalSection class guarantees

that the critical section objects are released when the protected code goes out of

scope, or if an exception occurs. In an adaptor, you typically want to protect the

frame acquisition loop in a critical section. Insert this code in the acquisition thread

function, just before the frame acquisition loop — see “Implementing the Acquisition

Thread Function” on page 5-18.

std::auto_ptr<imaqkit::IAutoCriticalSection>

myAutoSection(imaqkit::createAutoCriticalSection(adaptor->_mySection,

true));

In this code, the variable myAutoSection is a handle to an

IAutoCriticalSection object, that is managed as a Standard Template

Library auto_ptr. The code passes a handle to an ICriticalSection object,

_mySection, as an argument to the createAutoCriticalSection() function.

The second argument to createAutoCriticalSection() specifies that the

adaptor should enter the critical section automatically upon creation of the

IAutoCriticalSection.

At the end of the code that you want to protect, leave the critical section. In an

adaptor, you want to leave the critical section after the frame acquisition loop is