DTrace Variables

By Ifeyinwa Okoye and John Stearns, August 2006

DTrace Variables

Variable	Description	Usage

Scalar	Used to represent fixed-size data objects. They could be individual such as pointers and integers or composite such as arrays.	`x=123` (scalar variable x of type integer)
Associative array	Used to represent collections of data elements that can be retrieved by specifying a key. There is no predefined limit of the number of elements. Elements can be indexed by any tuple, and elements are not stored in preallocated consecutive storage locations.	`a[123,“hello”] = 56` (associative array a with key, [int, string])
Thread-Local	Used to declare variable storage that is local to each operating system thread.	`self->x= 45` (thread-local variable x of type integer)
Clause-Local	This variable is active for the lifetime of a given probe clause and its storage is reused for each D program clause.	`this->c='D'` (character clause-local variable c)
Built-in	All these variables are scalar global variables.	--
External	The backquote character ( `) is a scoping operator for accessing variables that are defined in the OS and not in your D program.	`kmem_flags (accessing a C variable in the kernel source code)