Last modified on 20 September 2006, at 20:59

Ada Programming/Libraries/GNAT.Bounded Buffers

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--  This package provides a thread-safe generic bounded buffer abstraction.
--  Instances are useful directly or as parts of the implementations of other
--  abstractions, such as mailboxes.

--  Bounded_Buffer is declared explicitly as a protected type, rather than as
--  a simple limited private type completed as a protected type, so that
--  clients may make calls accordingly (i.e., conditional/timed entry calls).

with System;

generic
   type Element is private;
   --  The type of the values contained within buffer objects

package GNAT.Bounded_Buffers is
   pragma Pure;

   type Content is array (Positive range <>) of Element;
   --  Content is an internal artefact that cannot be hidden because protected
   --  types cannot contain type declarations.

   Default_Ceiling : constant System.Priority := System.Default_Priority;
   --  A convenience value for the Ceiling discriminant

   protected type Bounded_Buffer
      (Capacity : Positive;
      --  Objects of type Bounded_Buffer specify the maximum number of Element
      --  values they can hold via the discriminant Capacity.

      Ceiling : System.Priority)
      --  Users must specify the ceiling priority for the object. If the
      --  Real-Time Systems Annex is not in use this value is not important.
   is
      pragma Priority (Ceiling);

      entry Insert (Item : Element);
      --  Insert Item into the buffer, blocks caller until space is available

      entry Remove (Item : out Element);
      --  Remove next available Element from buffer. Blocks caller until an
      --  Element is available.

      function Empty return Boolean;
      --  Returns whether the instance contains any Elements.
      --  Note: State may change immediately after call returns.

      function Full return Boolean;
      --  Returns whether any space remains within the instance.
      --  Note: State may change immediately after call returns.

      function Extent return Natural;
      --  Returns the number of Element values currently held
      --  within the instance.
      --  Note: State may change immediately after call returns.

   private
      Values   : Content (1 .. Capacity);
      --  The container for the values held by the buffer instance

      Next_In  : Positive := 1;
      --  The index of the next Element inserted. Wraps around

      Next_Out : Positive := 1;
      --  The index of the next Element removed. Wraps around

      Count    : Natural  := 0;
      --  The number of Elements currently held
   end Bounded_Buffer;

end GNAT.Bounded_Buffers;