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D.7 Tasking Restrictions

This clause defines restrictions that can be used with a pragma Restrictions (see 13.12) to facilitate the construction of highly efficient tasking run-time systems.

Static Semantics

The following restriction_identifiers are language defined:

No_Task_Hierarchy

All (nonenvironment) tasks depend directly on the environment task of the partition.

No_Nested_Finalization

Objects with controlled parts and access types that designate such objects shall be declared only at library level.

No_Abort_Statements

There are no abort_statements, and there are no calls on Task_Identification.Abort_Task.

No_Terminate_Alternatives

There are no selective_accepts with terminate_alternatives.

No_Task_Allocators

There are no allocators for task types or types containing task subcomponents.

No_Implicit_Heap_Allocations

There are no operations that implicitly require heap storage allocation to be performed by the implementation. The operations that implicitly require heap storage allocation are implementation defined.

No_Dynamic_Priorities

There are no semantic dependences on the package Dynamic_Priorities.

No_Asynchronous_Control

There are no semantic dependences on the package Asynchronous_Task_Control.

The following restriction_parameter_identifiers are language defined:

Max_Select_Alternatives

Specifies the maximum number of alternatives in a selective_accept.

Max_Task_Entries

Specifies the maximum number of entries per task. The bounds of every entry family of a task unit shall be static, or shall be defined by a discriminant of a subtype whose corresponding bound is static. A value of zero indicates that no rendezvous are possible.

Max_Protected_Entries

Specifies the maximum number of entries per protected type. The bounds of every entry family of a protected unit shall be static, or shall be defined by a discriminant of a subtype whose corresponding bound is static.

Dynamic Semantics

If the following restrictions are violated, the behavior is implementation defined. If an implementation chooses to detect such a violation, Storage_Error should be raised.

The following restriction_parameter_identifiers are language defined:

Max_Storage_At_Blocking

Specifies the maximum portion (in storage elements) of a task's Storage_Size that can be retained by a blocked task.

Max_Asynchronous_Select_Nesting

Specifies the maximum dynamic nesting level of asynchronous_selects. A value of zero prevents the use of any asynchronous_select.

Max_Tasks

Specifies the maximum number of task creations that may be executed over the lifetime of a partition, not counting the creation of the environment task.

It is implementation defined whether the use of pragma Restrictions results in a reduction in executable program size, storage requirements, or execution time. If possible, the implementation should provide quantitative descriptions of such effects for each restriction.

Implementation Advice

When feasible, the implementation should take advantage of the specified restrictions to produce a more efficient implementation.

NOTES

(29) The above Storage_Checks can be suppressed with pragma Suppress.

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