D.4.1 Admission Policies
This subclause specifies a mechanism for a user to
choose an admission policy. It also defines one such policy. Other policies
are implementation defined.
Syntax
The form of a
pragma
Admission_Policy is as follows:
Legality Rules
The
policy_identifier
shall be either FIFO_Spinning or an implementation-defined identifier.
Post-Compilation Rules
An Admission_Policy pragma is a configuration pragma.
Dynamic Semantics
An admission policy governs the order in which competing
tasks are evaluated for acquiring the execution resource associated with
a protected object. The admission policy is specified by an Admission_Policy
pragma.
One admission policy, FIFO_Spinning, is language
defined. If FIFO_Spinning is in effect, and starting a protected action
on a protected object involves busy-waiting, then calls are selected
for acquiring the execution resource of the protected object in the order
in which the busy-wait was initiated; otherwise the FIFO_Spinning policy
has no effect. If no Admission_Policy pragma applies to any of the program
units in the partition, the admission policy for that partition is implementation
defined.
Implementation Permissions
Implementations are allowed to define other admission
policies, but are not required to support specifying more than one admission
policy per partition.
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