1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT LIBRARY COMPONENTS                          --
4--                                                                          --
5--                  G N A T . B O U N D E D _ B U F F E R S                 --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--                     Copyright (C) 2003-2019, AdaCore                     --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- It is now maintained by Ada Core Technologies Inc (http://www.gnat.com). --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  This package provides a thread-safe generic bounded buffer abstraction.
33--  Instances are useful directly or as parts of the implementations of other
34--  abstractions, such as mailboxes.
35
36--  Bounded_Buffer is declared explicitly as a protected type, rather than as
37--  a simple limited private type completed as a protected type, so that
38--  clients may make calls accordingly (i.e., conditional/timed entry calls).
39
40with System;
41
42generic
43   type Element is private;
44   --  The type of the values contained within buffer objects
45
46package GNAT.Bounded_Buffers is
47   pragma Pure;
48
49   type Content is array (Positive range <>) of Element;
50   --  Content is an internal artefact that cannot be hidden because protected
51   --  types cannot contain type declarations.
52
53   Default_Ceiling : constant System.Priority := System.Default_Priority;
54   --  A convenience value for the Ceiling discriminant
55
56   protected type Bounded_Buffer
57      (Capacity : Positive;
58      --  Objects of type Bounded_Buffer specify the maximum number of Element
59      --  values they can hold via the discriminant Capacity.
60
61      Ceiling : System.Priority)
62      --  Users must specify the ceiling priority for the object. If the
63      --  Real-Time Systems Annex is not in use this value is not important.
64   is
65      pragma Priority (Ceiling);
66
67      entry Insert (Item : Element);
68      --  Insert Item into the buffer, blocks caller until space is available
69
70      entry Remove (Item : out Element);
71      --  Remove next available Element from buffer. Blocks caller until an
72      --  Element is available.
73
74      function Empty return Boolean;
75      --  Returns whether the instance contains any Elements.
76      --  Note: State may change immediately after call returns.
77
78      function Full return Boolean;
79      --  Returns whether any space remains within the instance.
80      --  Note: State may change immediately after call returns.
81
82      function Extent return Natural;
83      --  Returns the number of Element values currently held
84      --  within the instance.
85      --  Note: State may change immediately after call returns.
86
87   private
88      Values   : Content (1 .. Capacity);
89      --  The container for the values held by the buffer instance
90
91      Next_In  : Positive := 1;
92      --  The index of the next Element inserted. Wraps around
93
94      Next_Out : Positive := 1;
95      --  The index of the next Element removed. Wraps around
96
97      Count    : Natural  := 0;
98      --  The number of Elements currently held
99   end Bounded_Buffer;
100
101end GNAT.Bounded_Buffers;
102