5.5.4 Data Scoping Attributes

The OpenMP 3.0 specification version 3.0 (in section 2.9) describes how the data-sharing attributes of variables referenced in parallel, task, and worksharing regions are determined.

The data-sharing attributes of variables referenced in a construct may be one of the following: predetermined, explicitly determined, or implicitly determined. Variables with explicitly determined data-sharing attributes are those that are referenced in a given construct and are listed in a data-sharing attribute clause on the construct. Variables with implicitly determined data-sharing attributes are those that are referenced in a given construct, do not have predetermined data-sharing attributes, and are not listed in a data-sharing attribute clause on the construct.

The rules for how the data-sharing attributes of variables are implicitly determined may not always be obvious (see 5.2 Data Environment). It is therefore recommended that to avoid any surprises, the programmer explicitly scope all variables that are referenced in a task construct (using the default, shared, private, and firstprivate clauses), rather than rely on the OpenMP implicit scoping rules.