lastprivate Clause

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

5.4.5 lastprivate Clause


Name: lastprivate	Properties: data-environment attribute, data-sharing attribute, privatization

Arguments


Name	Type	Properties

list	list of variable list item type	default

Modiﬁers


Name	Modiﬁes	Type	Properties

lastprivate-modiﬁer	list	Keyword: conditional	default

Directives

distribute, do, for, loop, sections, simd, taskloop

Semantics

The lastprivate clause provides a superset of the functionality provided by the private clause. A list item that appears in a lastprivate clause is subject to the private clause semantics described in Section 5.4.3. In addition, when a lastprivate clause without the conditional modiﬁer appears on a directive and the list item is not an iteration variable of any associated loop, the value of each new list item from the sequentially last iteration of the associated loops, or the lexically last structured block sequence associated with a sections construct, is assigned to the original list item. When the conditional modiﬁer appears on the clause or the list item is an iteration variable of one of the associated loops, if sequential execution of the loop nest would assign a value to the list item then the original list item is assigned the value that the list item would have after sequential execution of the loop nest.

For class types, the copy assignment operator is invoked. The order in which copy assignment operators for diﬀerent variables of the same class type are invoked is unspeciﬁed.

For an array of elements of non-array type, each element is assigned to the corresponding element of the original array.

If the original list item does not have the POINTER attribute, its update occurs as if by intrinsic assignment unless it has a type bound procedure as a deﬁned assignment.

If the original list item has the POINTER attribute, its update occurs as if by pointer assignment.

When the conditional modiﬁer does not appear on the lastprivate clause, any list item that is not an iteration variable of the associated loops and that is not assigned a value by the sequentially last iteration of the loops, or by the lexically last structured block sequence associated with a sections construct, has an unspeciﬁed value after the construct. When the conditional modiﬁer does not appear on the lastprivate clause, a list item that is the iteration variable of an associated loop and that would not be assigned a value during sequential execution of the loop nest has an unspeciﬁed value after the construct. Unassigned subcomponents also have unspeciﬁed values after the construct.

If the lastprivate clause is used on a construct to which neither the nowait nor the nogroup clauses are applied, the original list item becomes deﬁned at the end of the construct. To avoid data races, concurrent reads or updates of the original list item must be synchronized with the update of the original list item that occurs as a result of the lastprivate clause.

Otherwise, if the lastprivate clause is used on a construct to which the nowait or the nogroup clauses are applied, accesses to the original list item may create a data race. To avoid this data race, if an assignment to the original list item occurs then synchronization must be inserted to ensure that the assignment completes and the original list item is ﬂushed to memory.

If a list item that appears in a lastprivate clause with the conditional modiﬁer is modiﬁed in the region by an assignment outside the construct or not to the list item then the value assigned to the original list item is unspeciﬁed.

Restrictions

Restrictions to the lastprivate clause are as follows:

A list item must not appear in a lastprivate clause on a work-distribution construct if the corresponding region binds to the region of a parallelism-generating construct in which the list item is private.
A list item that appears in a lastprivate clause with the conditional modiﬁer must be a scalar variable.

∙ A variable of class type (or array thereof) that appears in a lastprivate clause requires an accessible, unambiguous default constructor for the class type, unless the list item is also speciﬁed in a firstprivate clause. ∙ A variable of class type (or array thereof) that appears in a lastprivate clause requires an accessible, unambiguous copy assignment operator for the class type. ∙ If an original list item in a lastprivate clause on a work-distribution construct has a reference type then it must bind to the same object for all threads in the binding thread set of the work-distribution region.

∙ A variable that appears in a lastprivate clause must be deﬁnable. ∙ If the original list item has the ALLOCATABLE attribute, the corresponding list item of which the value is assigned to the original item must have an allocation status of allocated upon exit from the sequentially last iteration or lexically last structured block sequence associated with a sections construct. ∙ If the list item is a polymorphic variable with the ALLOCATABLE attribute, the behavior is unspeciﬁed.

Cross References

distribute directive, see Section 11.6
do directive, see Section 11.5.2
for directive, see Section 11.5.1
loop directive, see Section 11.7
private clause, see Section 5.4.3
sections directive, see Section 11.3
simd directive, see Section 10.4
taskloop directive, see Section 12.6

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