cancellation point Construct

| OPENMP API Specification: "Version 5.2 -- GIT rev 95b2e3a44"

16.2 cancellation point Construct


Name: cancellation point	Association: none
Category: executable	Properties: default

Clauses

do, for, parallel, sections, taskgroup

Additional information

The cancel-directive-name clause set consists of the directive-name of each directive that has the cancellable property (i.e., directive-name for the worksharing-loop construct, parallel, sections and taskgroup). This clause set has the required, unique and exclusive properties.

Binding

The binding thread set of the cancellation point construct is the current team. The binding region of the cancellation point region is the innermost enclosing region of the type that corresponds to cancel-directive-name.

Semantics

The cancellation point construct introduces a user-deﬁned cancellation point at which an implicit or explicit task must check if cancellation of the innermost enclosing region of the type speciﬁed by cancel-directive-name, which must be the directive-name of a cancellable construct, has been activated. This construct does not implement any synchronization between threads or tasks. When an implicit or explicit task reaches a user-deﬁned cancellation point and if the cancel-var ICV is true, then:

If the cancel-directive-name of the encountered cancellation point construct is not taskgroup, the thread continues execution at the end of the canceled region if cancellation has been activated for the innermost enclosing region of the type speciﬁed.
If the cancel-directive-name of the encountered cancellation point construct is taskgroup, the encountering task checks for active cancellation of all taskgroup sets to which the encountering task belongs and continues execution at the end of the current task region if cancellation has been activated for any of them.

Execution Model Events

The cancellation event occurs if a task encounters a cancellation point and detects the activation of cancellation.

Tool Callbacks

A thread dispatches a registered ompt_callback_cancel callback for each occurrence of a cancel event in the context of the encountering task. This callback has type signature ompt_callback_cancel_t; (ﬂags & ompt_cancel_detected) always evaluates to true in the dispatched callback; (ﬂags & ompt_cancel_parallel) evaluates to true in the dispatched callback if cancel-directive-name of the encountered cancellation point construct is parallel; (ﬂags & ompt_cancel_sections) evaluates to true in the dispatched callback if cancel-directive-name of the encountered cancellation point construct is sections; (ﬂags & ompt_cancel_loop) evaluates to true in the dispatched callback if cancel-directive-name of the encountered cancellation point construct is for or do; and (ﬂags & ompt_cancel_taskgroup) evaluates to true in the dispatched callback if cancel-directive-name of the encountered cancellation point construct is taskgroup.

Restrictions

Restrictions to the cancellation point construct are as follows:

A cancellation point construct for which cancel-directive-name is taskgroup must be closely nested inside a task or taskloop construct, and the cancellation point region must be closely nested inside a taskgroup region.
A cancellation point construct for which cancel-directive-name is not taskgroup must be closely nested inside an OpenMP construct that matches cancel-directive-name.

Cross References

omp_get_cancellation, see Section 18.2.8
ompt_callback_cancel_t, see Section 19.5.2.18
cancel-var ICV, see Section 2.1
do directive, see Section 11.5.2
for directive, see Section 11.5.1
parallel directive, see Section 10.1
sections directive, see Section 11.3
taskgroup directive, see Section 15.4

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