cc_lockset.h

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/* -*- C++ -*- */

//=============================================================================
/**
 *  @file      CC_LockSet.h
 *
 *  CC_LockSet.h,v 1.23 2003/12/29 15:16:30 dhinton Exp
 *
 *    This class implements the lock set interface from the
 *    concurrency service.
 *
 *    In the present implementation the multiple possesion semantics
 *    is implemented for non-transactional clients. In future
 *    versions this should be changed because the multiple possesion
 *    semantics does not apply to non-transactional clients. This
 *    can be accomplished in the following manner:
 *    - Make a class with the same functiallity as the CC_LockSet
 *      class as a base class for both implementations.
 *    - The functionallity that should be separated out in the
 *      subclasses is the compatible function which should always
 *      return false because no locks can be held simultanously with
 *      non-transactional clients.
 *    - Use these classes from the classes that inherits the
 *      servant properties, i.e. the way CC_LockSet does now.
 *
 *
 *  @author   Torben Worm <[e-mail]>
 */
//=============================================================================


#ifndef _CC_LOCKSET_H
#define _CC_LOCKSET_H

#include /**/ "ace/pre.h"

#include "ace/config-all.h"

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#include "ace/Thread_Mutex.h"
#include "ace/Token.h"
#include "ace/Unbounded_Queue.h"

#include "orbsvcs/CosConcurrencyControlS.h"
#include "concurrency_export.h"

#if defined (lock_held)
#undef lock_held
#endif /* lock_held */

/// This constant defines the number of lock modes. There is really no
/// way to set this constant dynamically because the nuber of lock
/// modes are not stated as part of the IDL.
#define NUMBER_OF_LOCK_MODES 5

/// Enummeration representing the lock modes. The incoming request is
/// always converted to this representation. There are two reasons for
/// this: Firstly the lock modes are ordered from weakest to strongest
/// in the internal representation, and secondly it is possible to
/// indicate a 'non-mode' (CC_EM)
typedef enum {CC_EM=-1, CC_IR=0, CC_R, CC_U, CC_IW, CC_W} CC_LockModeEnum;

/**
 * @class CC_LockSet
 *
 * @brief CC_LockSet
 *
 * This class implements the LockSet interface that is part of
 * the CosConcurrency service. Please consult the idl file for
 * detailed descriptions apart from the comments in this file At
 * present the lock set is not really a set, but only one lock.
 */
class TAO_Concurrency_Export CC_LockSet :  public POA_CosConcurrencyControl::LockSet
{
public:

  // = Initialization and termination methods.
  /// Default constructor
  CC_LockSet (void);

  /// Constructor used if create_related is used to create the lock
  /// set.
  CC_LockSet (CosConcurrencyControl::LockSet_ptr related);

  /// Destructor.
  ~CC_LockSet (void);

  // = CosConcurrencyControl methods
  /// Acquires this lock. Blocks until lock is obtained
  virtual void lock (CosConcurrencyControl::lock_mode mode
                     ACE_ENV_ARG_DECL)
    ACE_THROW_SPEC ((CORBA::SystemException));

  /// Tries to acquire this lock. If it is not possible to acquire the
  /// lock, false is returned
  virtual CORBA::Boolean try_lock (CosConcurrencyControl::lock_mode mode
                                   ACE_ENV_ARG_DECL)
    ACE_THROW_SPEC ((CORBA::SystemException));

  /// Releases this lock.
  virtual void unlock (CosConcurrencyControl::lock_mode mode
                       ACE_ENV_ARG_DECL)
    ACE_THROW_SPEC ((CORBA::SystemException,
                     CosConcurrencyControl::LockNotHeld));

  /// Changes the mode of this lock.
  virtual void change_mode (CosConcurrencyControl::lock_mode held_mode,
                            CosConcurrencyControl::lock_mode new_mode
                            ACE_ENV_ARG_DECL)
    ACE_THROW_SPEC ((CORBA::SystemException,
                     CosConcurrencyControl::LockNotHeld));

  // = Debugging methods
  /// Dump the state of the object to stdout
  void dump (void);

private:
  /// Converts the CORBA specification's lock mode to the internal
  /// representation
  CC_LockModeEnum lmconvert (CosConcurrencyControl::lock_mode mode);

  /// Initiatlizes the lock set array and acquires the initial
  /// semaphore.
  void Init (ACE_ENV_SINGLE_ARG_DECL);

  /// Returns true if the held lock and the requested lock are compatible
  CORBA::Boolean compatible (CC_LockModeEnum mr);

  // The _i functions below ensures atomical access the the state data
  // for the lock set. The functions acquires a thread lock in order
  // to insure consistency within the lock set. The return value
  // typically indicates whether the current thread should be
  // suspended or not (by locking the semaphore.

  /// Locks the access to the data and decides whether to lock or
  /// not. Returns 1 if the semaphore should be locked.
  int lock_i (CC_LockModeEnum lm);

  // int unlock_i (CosConcurrencyControl::lock_mode lm);
  // This function is not necessary because we lock access to the data
  // and unlocks the semaphore until an invalid lock mode is first on
  // the queue. Thereafter we release the lock.

  /// Locks the access to the data and determines whether to return
  /// true or false. Returns 1 if true should be returned.
  int try_lock_i (CC_LockModeEnum lm);

  /// Locks access to the data and determines if the semaphore should
  /// be locked. Returns 1 if the semaphore should be locked.
  int change_mode_i (CC_LockModeEnum lm_held,
                     CC_LockModeEnum lm_new);

  /// Locks access ti the data and checks whether the lock is held.
  int lock_held (CC_LockModeEnum lm);

  /// An array of lock counters that counts how many locks of that type
  /// that the lock set holds.
  int lock_[NUMBER_OF_LOCK_MODES];

  // ACE_Thread_Semaphore semaphore_;
  /**
   * This is the semaphore for the lock set. The semaphore is used to
   * queue requests for locks in modes stronger than currently
   * possible to grant.  Note that the <ACE_Token> provides strict
   * FIFO ordering of acquisition/release of the lock.
   */
  ACE_Token semaphore_;

  /**
   * If this lock set is related to another lock set, this is the
   * pointer to the related lock set. This is a really simple
   * solution, but since transactions are not supported in the first
   * version there should be no reason to drop lock sets together. The
   * <LockSetCoordinator> is not implemented (it has the
   * responsibilities of dropping the locks).
   */
  CosConcurrencyControl::LockSet_ptr related_lockset_;

  /// Mapping between requested and held lock modes. Used by compatible
  /// (...).  Uses the internal enumeration as indices.
  static CORBA::Boolean compatible_[NUMBER_OF_LOCK_MODES][NUMBER_OF_LOCK_MODES];

  /// Lock to ensure that race conditions does not occur.
  TAO_SYNCH_MUTEX mlock_;

  /// Queue to hold the requested locks not yet granted.
  ACE_Unbounded_Queue <CC_LockModeEnum> lock_queue_;
};

#include /**/ "ace/post.h"

#endif /* _CC_LOCKSET_H */