Metered concurrency: Difference between revisions
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The interface for the counting semaphore is defined in an Ada package specification: |
The interface for the counting semaphore is defined in an Ada package specification: |
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< |
<lang ada> package Semaphores is |
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protected type Counting_Semaphore(Max : Positive) is |
protected type Counting_Semaphore(Max : Positive) is |
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entry Acquire; |
entry Acquire; |
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Lock_Count : Natural := 0; |
Lock_Count : Natural := 0; |
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end Counting_Semaphore; |
end Counting_Semaphore; |
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end Semaphores;</ |
end Semaphores;</lang> |
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The ''Acquire'' entry has a condition associated with it. A task can only execute the ''Acquire'' entry when ''Lock_Count'' is less than ''Max''. This is the key to making this structure behave as a counting semaphore. This condition, and all the other aspects of ''Counting_Semaphore'' are contained in the package body. |
The ''Acquire'' entry has a condition associated with it. A task can only execute the ''Acquire'' entry when ''Lock_Count'' is less than ''Max''. This is the key to making this structure behave as a counting semaphore. This condition, and all the other aspects of ''Counting_Semaphore'' are contained in the package body. |
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< |
<lang ada> package body Semaphores is |
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------------------------ |
------------------------ |
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end Counting_Semaphore; |
end Counting_Semaphore; |
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end Semaphores;</ |
end Semaphores;</lang> |
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We now need a set of tasks to properly call an instance of ''Counting_Semaphore''. |
We now need a set of tasks to properly call an instance of ''Counting_Semaphore''. |
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< |
<lang ada> with Semaphores; |
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with Ada.Text_Io; use Ada.Text_Io; |
with Ada.Text_Io; use Ada.Text_Io; |
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