7.1  OpenMP Contexts

At any point in a program, an OpenMP context exists that defines traits that describe the active OpenMP constructs, the execution devices, functionality supported by the implementation and available dynamic values. The traits are grouped into trait sets. The following trait sets exist: construct, device, target_device, implementation and dynamic. Traits are categorized as name-list traits, clause-list traits, non-property traits and extension traits. This categorization determines the syntax that is used to match the trait, as defined in Section 7.2.

The construct set is composed of the directive names, each being a trait, of all enclosing constructs at that point in the program up to a target construct. Combined and composite constructs are added to the set as distinct constructs in the same nesting order specified by the original construct. Whether the dispatch construct is added to the construct set is implementation defined. If it is added, it will only be added for the target-call of the associated code. The set is ordered by nesting level in ascending order. Specifically, the ordering of the set of constructs is c₁, …, c_N, where c₁ is the construct at the outermost nesting level and c_N is the construct at the innermost nesting level. In addition, if the point in the program is not enclosed by a target construct, the following rules are applied in order:

1.

For procedures with a declare simd directive, the simd trait is added to the beginning of the set as c₁ for any generated SIMD versions so the total size of the set is increased by one.

2.

For procedures that are determined to be function variants by a declare variant directive, the selectors c₁, …, c_M of the construct selector set are added in the same order to the beginning of the set as c₁, …, c_M so the total size of the set is increased by M.

3.

For procedures that are determined to be target function variants by a declare target directive, the target trait is added to the beginning of the set as c₁ so the total size of the set is increased by one.

The simd trait is a clause-list trait that is defined with properties that match the clauses accepted by the declare simd directive with the same name and semantics. The simd trait defines at least the simdlen property and one of the inbranch or notinbranch properties. Traits in the construct set other than simd are non-property traits.

The device set includes traits that define the characteristics of the device being targeted by the compiler at that point in the program. For each target device that the implementation supports, a target_device set exists that defines the characteristics of that device. At least the following traits must be defined for the device and all target_device sets:

• The kind(kind-name-list) trait specifies the general kind of the device. The following kind-name values are defined:

  • host, which specifies that the device is the host device;
  • nohost, which specifies that the device is not the host device; and
  • the values defined in the OpenMP Additional Definitions document.
• The isa(isa-name-list) trait specifies the Instruction Set Architectures supported by the device. The accepted isa-name values are implementation defined.
• The arch(arch-name-list) trait specifies the architectures supported by the device. The accepted arch-name values are implementation defined.

The kind, isa and arch traits in the device and target_device sets are name-list traits.

Additionally, the target_device set defines the following trait:

• The device_num trait specifies the device number of the device.

The implementation set includes traits that describe the functionality supported by the OpenMP implementation at that point in the program. At least the following traits can be defined:

• The vendor(vendor-name-list) trait, which specifies the vendor identifiers of the implementation. OpenMP defined values for vendor-name are defined in the OpenMP Additional Definitions document.
• The extension(extension-name-list) trait, which specifies vendor specific extensions to the OpenMP specification. The accepted extension-name values are implementation defined.
• A trait with a name that is identical to the name of any clause that was supplied to the requires directive prior to the program point. Such traits other than the atomic_default_mem_order trait are non-property traits. The presence of these traits has been deprecated.
• A requires(requires-clause-list) trait, which is a clause-list trait for which the properties are the clauses that have been supplied to the requires directive prior to the program point as well as implementation-defined implicit requirements.

The vendor and extension traits in the implementation set are name-list traits.

Implementations can define additional traits in the device, target_device and implementation sets; these traits are extension traits.

The dynamic trait set includes traits that define the dynamic properties of a program at a point in its execution. The data state trait in the dynamic trait set refers to the complete data state of the program that may be accessed at runtime.