------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . M U L T I P R O C E S S O R S . F A I R _ L O C K S --
-- --
-- S p e c --
-- --
-- Copyright (C) 2010-2023, AdaCore --
-- --
-- GNARL 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. GNARL 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 --
-- <http://www.gnu.org/licenses/>. --
-- --
------------------------------------------------------------------------------
with System.Multiprocessors.Spin_Locks;
package System.Multiprocessors.Fair_Locks is
pragma Preelaborate;
-- Note: The locks implemented in this package are fair among CPUs. Using
-- this package to synchronize tasks assigned to the same CPU may result
-- in a dead lock.
---------------
-- Fair lock --
---------------
type Spinning_Array is array (CPU) of Boolean;
pragma Volatile_Components (Spinning_Array);
type Fair_Lock is limited record
Spinning : Spinning_Array := (others => False);
Lock : Spin_Locks.Spin_Lock;
end record;
-- Note: the default value of a Fair_Lock is the unlocked state
procedure Initialize (Flock : in out Fair_Lock);
pragma Inline (Initialize);
-- Initialize the lock
procedure Lock (Flock : in out Fair_Lock);
pragma Inline (Lock);
-- Loop until lock is acquired
function Locked (Flock : Fair_Lock) return Boolean;
pragma Inline (Locked);
-- Return the current state of the lock
procedure Try_Lock (Flock : in out Fair_Lock; Succeeded : out Boolean);
pragma Inline (Try_Lock);
-- Return True if the lock has been acquired, otherwise don't wait for the
-- lock and return False.
procedure Unlock (Flock : in out Fair_Lock);
pragma Inline (Unlock);
-- Release the lock and wake up the next waiting CPU (if any)
end System.Multiprocessors.Fair_Locks;