DEPEND Clause

Parallel Directive Clause: Enforces additional constraints on the scheduling of a task by enabling dependences between sibling tasks in the task region.

It takes one of the following forms:

In Synchronization Directive !$OMP ORDERED

DEPEND (SOURCE) -or-

DEPEND (SINK:vec)

In all other directives:

DEPEND (dependence-type : list)

dependence-type	Can be any one of the following clauses: IN, OUT, or INOUT, MUTEXINOUTSET, or INOUTSET. If one or more of the `list` items specified in an IN `dependence-type` is the same as a `list` item appearing in a DEPEND clause with an OUT, INOUT, MUTEXINOUTSET or INOUTSET `dependence-type` on a construct that previously generated a sibling task, the generated task is a dependent task of the sibling task. If one or more of the `list` items specified in an OUT or INOUT `dependence-type` is the same as a `list` item appearing in a DEPEND clause with an IN, OUT, INOUT, MUTEXINOUTSET, or INOUTSET `dependence-type` on a construct that previously generated a sibling task, the generated task is a dependent task of the sibling task. If one or more of the `list` items specified in an MUTEXINOUTSET `dependence-type` is the same as a `list` item appearing in a DEPEND clause with an IN, OUT, INOUT, or INOUTSET `dependence-type` on a construct that previously generated a sibling task, the generated task is a dependent task of the sibling task. If a `list` item specified in a MUTEXINOUTSET `dependence-type` is the same as a `list` item appearing in a DEPEND clause with a MUTEXINOUTSET `dependence-type` on a different task generating construct and both constructs generate sibling tasks, the sibling tasks are mutually exclusive. If one or more of the `list` items specified in an INOUTSET `dependence-type` is the same as a `list` item appearing in a DEPEND clause with an IN, OUT, INOUT, or MUTEXINOUTSET `dependence-type` on a construct that previously generated a sibling task, the generated task is a dependent task of the sibling task.
list	Is one or more variables or non-zero length array sections. Any `list` items used in a DEPEND clause of the same task or sibling tasks must indicate identical storage or disjoint storage. The list items that appear in the DEPEND clause may include array sections. Zero-sized arrays and common block names are not permitted as list items. The behavior is undefined in these cases: If a `list` item has the POINTER attribute and its association status is disassociated or undefined If a `list` item has the ALLOCATABLE attribute and its allocation status is unallocated Note that this enforced task dependence establishes a synchronization of accesses to each `list` item performed by a dependent task, with respect to accesses to the same `list` item performed by any previous tasks. You must properly synchronize access with respect to other concurrent accesses to each `list` item.
SOURCE	Specifies the satisfaction of cross-iteration dependences that arise from the current iteration.
SINK	Specifies a cross-iteration dependence, where the iteration vector `vec` indicates the iteration that satisfies the dependence.
vec	Is the iteration vector. It has the form: where n is the value specified by the ORDERED clause in the DO loop directive, x_i denotes the loop iteration variable of the i-th nested loop associated with the loop directive, and d_i is a non-negative integer scalar constant. If `vec` does not occur in the iteration space, the DEPEND clause is ignored. Note that if `vec` does not indicate a lexicographically earlier iteration, it can cause a deadlock. For a `vec` element form of x_i + d_i or x_i - d_i, the expression x_i + d_i or x_i - d_i for any value of the integer loop iteration variable x_i that can encounter the ordered construct must be computable in the loop iteration variable's type without overflow.

If a DEPEND clause appears in a TARGET or TARGET UPDATE directive, it is treated as if it had appeared on the implicit task construct that encloses the TARGET construct.