------------------------------------------------------------------------------ -- -- -- GNAT LIBRARY COMPONENTS -- -- -- -- ADA.CONTAINERS.UNBOUNDED_PRIORITY_QUEUES -- -- -- -- S p e c -- -- -- -- Copyright (C) 2011-2021, Free Software Foundation, Inc. -- -- -- -- This specification is derived from the Ada Reference Manual for use with -- -- GNAT. The copyright notice above, and the license provisions that follow -- -- apply solely to the contents of the part following the private keyword. -- -- -- -- GNAT is free software; you can redistribute it and/or modify it under -- -- terms of the GNU General Public License as published by the Free Soft- -- -- ware Foundation; either version 3, or (at your option) any later ver- -- -- sion. GNAT is distributed in the hope that it will be useful, but WITH- -- -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY -- -- or FITNESS FOR A PARTICULAR PURPOSE. -- -- -- -- As a special exception under Section 7 of GPL version 3, you are granted -- -- additional permissions described in the GCC Runtime Library Exception, -- -- version 3.1, as published by the Free Software Foundation. -- -- -- -- You should have received a copy of the GNU General Public License and -- -- a copy of the GCC Runtime Library Exception along with this program; -- -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see -- -- . -- -- -- -- This unit was originally developed by Matthew J Heaney. -- ------------------------------------------------------------------------------ with System; with Ada.Containers.Ordered_Sets; with Ada.Containers.Synchronized_Queue_Interfaces; generic with package Queue_Interfaces is new Ada.Containers.Synchronized_Queue_Interfaces (<>); type Queue_Priority is private; with function Get_Priority (Element : Queue_Interfaces.Element_Type) return Queue_Priority is <>; with function Before (Left, Right : Queue_Priority) return Boolean is <>; Default_Ceiling : System.Any_Priority := System.Priority'Last; package Ada.Containers.Unbounded_Priority_Queues is pragma Annotate (CodePeer, Skip_Analysis); pragma Preelaborate; package Implementation is -- All identifiers in this unit are implementation defined pragma Implementation_Defined; -- We use an ordered set to hold the queue elements. This gives O(lg N) -- performance in the worst case for Enqueue and Dequeue. -- Sequence_Number is used to distinguish equivalent items. Each Enqueue -- uses a higher Sequence_Number, so that a new item is placed after -- already-enqueued equivalent items. -- -- At any time, the first set element is the one to be dequeued next (if -- the queue is not empty). type Set_Elem is record Sequence_Number : Count_Type; Item : Queue_Interfaces.Element_Type; end record; function "=" (X, Y : Queue_Interfaces.Element_Type) return Boolean is (not Before (Get_Priority (X), Get_Priority (Y)) and then not Before (Get_Priority (Y), Get_Priority (X))); -- Elements are equal if neither is Before the other function "=" (X, Y : Set_Elem) return Boolean is (X.Sequence_Number = Y.Sequence_Number and then X.Item = Y.Item); -- Set_Elems are equal if the elements are equal, and the -- Sequence_Numbers are equal. This is passed to Ordered_Sets. function "<" (X, Y : Set_Elem) return Boolean is (if X.Item = Y.Item then X.Sequence_Number < Y.Sequence_Number else Before (Get_Priority (X.Item), Get_Priority (Y.Item))); -- If the items are equal, Sequence_Number breaks the tie. Otherwise, -- use Before. This is passed to Ordered_Sets. pragma Suppress (Container_Checks); package Sets is new Ada.Containers.Ordered_Sets (Set_Elem); end Implementation; use Implementation, Implementation.Sets; protected type Queue (Ceiling : System.Any_Priority := Default_Ceiling) with Priority => Ceiling is new Queue_Interfaces.Queue with overriding entry Enqueue (New_Item : Queue_Interfaces.Element_Type); overriding entry Dequeue (Element : out Queue_Interfaces.Element_Type); -- The priority queue operation Dequeue_Only_High_Priority had been a -- protected entry in early drafts of AI05-0159, but it was discovered -- that that operation as specified was not in fact implementable. The -- operation was changed from an entry to a protected procedure per the -- ARG meeting in Edinburgh (June 2011), with a different signature and -- semantics. procedure Dequeue_Only_High_Priority (At_Least : Queue_Priority; Element : in out Queue_Interfaces.Element_Type; Success : out Boolean); overriding function Current_Use return Count_Type; overriding function Peak_Use return Count_Type; private Q_Elems : Set; -- Elements of the queue Max_Length : Count_Type := 0; -- The current length of the queue is the Length of Q_Elems. This is the -- maximum value of that, so far. Updated by Enqueue. Next_Sequence_Number : Count_Type := 0; -- Steadily increasing counter end Queue; end Ada.Containers.Unbounded_Priority_Queues;