Variables in DTrace

D provides two basic types of variables for use in your tracing programs: scalar variables and associative arrays. This section explores the rules for D variables in more detail and how variables can be associated with different scopes. A special kind of array variable, called an aggregation, is discussed in DTrace Aggregations.

Note:

• Scalar variables and associative arrays have a global scope and are not multi-processor safe (MP-safe). It means that the value of these variables can be changed by more than one processor and thus there are chances that the variable can became corrupt.

• Aggregations are MP-safe even though they have a global scope.

This section covers the following types of variables:

• Scalar Variables

• Associative Arrays

• Thread-Local Variables

• Clause-Local Variables

• Built-In Variables

• External Variables