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{00355AI95−00355−01} [This clause defines the task dispatching policy Round_Robin_Within_Priorities and the package Round_Robin.]
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{00355AI95−00355−01} The policy_identifier Round_Robin_Within_Priorities is a task dispatching policy.
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{00355AI95−00355−01} The following language−defined library package exists:
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with System; with Ada.Real_Time; package Ada.Dispatching.Round_Robin is Default_Quantum : constant Ada.Real_Time.Time_Span := implementation−defined; procedure Set_Quantum (Pri : in System.Priority; Quantum : in Ada.Real_Time.Time_Span); procedure Set_Quantum (Low, High : in System.Priority; Quantum : in Ada.Real_Time.Time_Span); function Actual_Quantum (Pri : System.Priority) return Ada.Real_Time.Time_Span; function Is_Round_Robin (Pri : System.Priority) return Boolean; end Ada.Dispatching.Round_Robin;
4.a.1/2
Implementation defined: The value of Default_Quantum in Dispatching.Round_Robin.
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{00355AI95−00355−01} When task dispatching policy Round_Robin_Within_Priorities is the single policy in effect for a partition, each task with priority in the range of System.Interrupt_Priority is dispatched according to policy FIFO_Within_Priorities.
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{00355AI95−00355−01} The procedures Set_Quantum set the required Quantum value for a single priority level Pri or a range of priority levels Low .. High. If no quantum is set for a Round Robin priority level, Default_Quantum is used.
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{00355AI95−00355−01} The function Actual_Quantum returns the actual quantum used by the implementation for the priority level Pri.
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{00355AI95−00355−01} The function Is_Round_Robin returns True if priority Pri is covered by task dispatching policy Round_Robin_Within_Priorities; otherwise it returns False.
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{00355AI95−00355−01} A call of Actual_Quantum or Set_Quantum raises exception Dispatching.Dispatching_Policy_Error if a predefined policy other than Round_Robin_Within_Priorities applies to the specified priority or any of the priorities in the specified range.
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{00355AI95−00355−01} For Round_Robin_Within_Priorities, the dispatching rules for FIFO_Within_Priorities apply with the following additional rules:
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13.a/2
Ramification: Note that this happens even when the task is executing at a higher, inherited priority, and even if that higher priority is dispatched by a different policy than round robin.
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14.a/2
Ramification: In this case, it will be given a budget as described in the first bullet.
14.b/2
The rules for FIFO_Within_Priority (to which these bullets are added) say that a task that has its base priority set to a Round Robin priority is moved to the tail of the ready queue for its new priority level, and then will be given a budget as described in the first bullet. That happens whether or not the task's original base priority was a Round Robin priority.
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{00333AI95−00333−01} {00355AI95−00355−01} An implementation shall allow, for a single partition, both the task dispatching policy to be specified as Round_Robin_Within_Priorities and also the locking policy (see D.3) to be specified as Ceiling_Locking.
15.a/2
Reason: This is the preferred combination of the Round_Robin_Within_Priorities policy with a locking policy, and we want that combination to be portable.
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{00355AI95−00355−01} An implementation shall document the quantum values supported.
16.a.1/2
Documentation Requirement: The quantum values supported for round robin dispatching.
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{00355AI95−00355−01} An implementation shall document the accuracy with which it detects the exhaustion of the budget of a task.
17.a.1/2
Documentation Requirement: The accuracy of the detection of the exhaustion of the budget of a task for round robin dispatching.
NOTES
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16 {00355AI95−00355−01} Due to implementation constraints, the quantum value returned by Actual_Quantum might not be identical to that set with Set_Quantum.
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17 {00355AI95−00355−01} A task that executes continuously with an inherited priority will not be subject to round robin dispatching.
19.a/2
{00355AI95−00355−01} {extensions to Ada 95} Policy Round_Robin_Within_Priorities and package Dispatching.Round_Robin are new.