Ada Reference Manual (Ada 2022 Draft 34) — Legal Information

C.6.3 The Package System.Atomic_Operations.Test_and_Set

The language-defined package System.Atomic_Operations.Test_And_Set provides an operation to atomically set and clear an atomic flag object.

Static Semantics

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The library package System.Atomic_Operations.Test_And_Set has the following declaration:

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package System.Atomic_Operations.Test_And_Set
with Pure, Nonblocking is

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type Test_And_Set_Flag is mod implementation-defined
with Atomic, Default_Value => 0, Size => implementation-defined;

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   function Atomic_Test_And_Set
     (Item : aliased in out Test_And_Set_Flag) return Boolean
      with Convention => Intrinsic;

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   procedure Atomic_Clear
     (Item : aliased in out Test_And_Set_Flag)
      with Convention => Intrinsic;

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   function Is_Lock_Free
     (Item : aliased Test_And_Set_Flag) return Boolean
      with Convention => Intrinsic;

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end System.Atomic_Operations.Test_And_Set;

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Test_And_Set_Flag represents the state of an atomic flag object. An atomic flag object can either be considered to be set or cleared.

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Atomic_Test_And_Set performs an atomic test-and-set operation on Item. Item is set to some implementation-defined nonzero value. The function returns True if the previous contents were nonzero, and otherwise returns False.

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Atomic_Clear performs an atomic clear operation on Item. After the operation, Item contains 0. This call should be used in conjunction with Atomic_Test_And_Set.

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