Associative Arrays
arrays
introduction
associative arrays
introduction
SystemTap also supports the use of associative arrays. While an ordinary variable represents a single value, associative arrays can represent a collection of values. Simply put, an associative array is a collection of unique keys; each key in the array has a value associated with it.
arrays
introduction
key pairs
associative arrays
introduction
key pairs
key pairs
introduction
arrays
arrays
introduction
unique keys
associative arrays
introduction
unique keys
unique keys
introduction
arrays
arrays
introduction
associated values
associative arrays
introduction
associated values
associated values
introduction
arrays
arrays
introduction
index expression
associative arrays
introduction
index expression
index expression
introduction
arrays
Since associative arrays are normally processed in multiple probes (as we will demonstrate later), they are declared as global variables in the SystemTap script. The syntax for accessing an element in an associative array is similar to that of awk, and is as follows:
arrays
introduction
syntax
associative arrays
introduction
syntax
syntax
introduction
arrays
format
introduction
arrays
array_name[index_expression]
Here, the array_name is any arbitrary name the array uses. The index_expression is used to refer to a specific unique key in the array. To illustrate, let us try to build an array named foo that specifies the ages of three people (i.e. the unique keys): tom, dick, and harry. To assign them the ages (i.e. associated values) of 23, 24, and 25 respectively, we'd use the following array statements:
arrays
introduction
example
associative arrays
introduction
example
example
introduction
arrays
Basic Array Statements
foo["tom"] = 23
foo["dick"] = 24
foo["harry"] = 25
You can specify up to 5 index expressons in an array statement, each one delimited by a comma (,). This is useful if you wish to have a key that contains multiple pieces of information. The following line from uses 5 elements for the key: process ID, executable name, user ID, parent ID, and string "W". It associates the value of devname with that key.
device[pid(),execname(),uid(),ppid(),"W"] = devname
Important
All associate arrays must be declared as global, regardless of whether the associate array is used in one or multiple probes.