action In DTrace, the term action refers to the action statements taken when a probe fires, which are defined in an action clause. See clause.

adaptive mutex A mutex (mutual exclusion) lock type. When requested yet held by another thread, it will either spin if that other thread is currently executing on another CPU or block if it isn’t.

aggregating function A D built-in function that operates on aggregations. These include population functions, such as count(), avg(), sum(), and quantize(); processing functions such as normalize() and trunc(); and printa() for printing. (See the “Aggregations” section in Chapter 2.)

aggregation A special D variable type used to summarize data. They are prefixed with an at (@) sign, are populated by ...

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