lumiera_documentation/src/lib/sync-classlock.hpp

/*
  SYNC-CLASSLOCK.hpp  -  special case of object based locking tied directly to a type

   Copyright (C)
     2008,            Hermann Vosseler <Ichthyostega@web.de>
     2023,            Hermann Vosseler <Ichthyostega@web.de>

  **Lumiera** is free software; you can redistribute it and/or modify it
  under the terms of the GNU General Public License as published by the
  Free Software Foundation; either version 2 of the License, or (at your
  option) any later version. See the file COPYING for further details.

*/

/** @file sync-classlock.hpp
 ** A special implementation of lib::Sync, where the storage of the object monitor
 ** is associated directly to a type rather then to a single object instance. While
 ** being problematic in conjunction with static startup/shutdown, doing so is sometimes
 ** necessary to setup type based dispatcher tables, managing singleton creation etc.
 **
 ** @note simply using the ClassLock may cause a Monitor object (with a mutex) to be
 **       created at static initialisation and destroyed on application shutdown.
 ** @see depend.hpp usage example
 ** @see SyncClasslock_test
 */


#ifndef LIB_SYNC_CLASSLOCK_H
#define LIB_SYNC_CLASSLOCK_H

#include "lib/nobug-init.hpp"
#include "lib/zombie-check.hpp"
#include "lib/meta/util.hpp"
#include "lib/sync.hpp"


namespace lib {
  
  
  /**
   * A synchronisation protection guard employing a lock scoped
   * to the parameter type as a whole, not an individual instance.
   * After creating an instance, every other access specifying the same
   * type is blocked.
   * @note the Lock is recursive, because several instances within the same
   *       thread may want to acquire it at the same time without deadlock.
   * @note there is a design sloppiness, as two instantiations of the
   *       ClassLock template with differing CONF count as different type.
   *       Actually using two different configurations within for a single
   *       class X should be detected and flagged as error, but actually
   *       just two non-shared lock instances get created silently. Beware!
   * @see Sync::Lock the usual simple instance-bound variant
   */
  template<class X, class CONF = RecursiveLock_NoWait>
  class ClassLock
    : public Sync<CONF>::Lock
    {
      using Lock    = Sync<CONF>::Lock;
      using Monitor = sync::Monitor<CONF>;
      
      struct PerClassMonitor : Monitor {};
      
      Monitor&
      getPerClassMonitor()
        {
          static PerClassMonitor classMonitor;
          static ZombieCheck zombieCheck{util::typeStr(this)};
          
          zombieCheck();
          return classMonitor;
        }
      
    public:
      ClassLock()
        : Lock{getPerClassMonitor()}
        { }
    };
  
  
} // namespace lib
#endif /*LIB_SYNC_CLASSLOCK_H*/