Class ObjectLock

  • All Implemented Interfaces:
    DepositBox

    public final class ObjectLock
    extends java.lang.Object
    implements DepositBox
    Read/write locks and lock synchronization on an object. Each object is required to have one ObjectLock which at any given time may be unlocked, write locked by one transaction, or read locked by one or more transactions.

    In order to obtain a lock, the transaction must call one of the acquire, passing itself, the lock type and the lock timeout. The transaction must attempt to obtain only one lock at any given time by synchronizing all calls to one of the acquire. If the transaction has acquired a read lock it may attempt to re-acquire the read lock. If the transaction attempts to acquire a write lock the lock will be upgraded.

    A read lock cannot be acquired while there is a write lock on the object, and a write lock cannot be acquired while there is one or more read locks. If a lock cannot be acquired, the transaction will hold until the lock is available or timeout occurs. If timeout occured (or a dead lock has been detected), LockNotGrantedException is thrown. If the object has been delete while waiting for the lock, ObjectDeletedException is thrown.

    When the lock is acquired, the locked object is returned.

    The transaction must call release(org.castor.persist.TransactionContext) when the lock is no longer required, allowing other transactions to obtain a lock. The transaction must release all references to the object prior to calling release(org.castor.persist.TransactionContext).

    If the object has been deleted, the transaction must call delete(org.castor.persist.TransactionContext) instead of release(org.castor.persist.TransactionContext).

    Version:
    $Revision: 8294 $ $Date: 2006-04-25 15:08:23 -0600 (Tue, 25 Apr 2006) $
    Author:
    Assaf Arkin, Thomas Yip
    See Also:
    TransactionContext
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      (package private) static class  ObjectLock.LinkedTx
      Object uses to hold a linked list of transactions holding write locks or waiting for a read/write lock.
    • Constructor Summary

      Constructors 
      Constructor Description
      ObjectLock​(OID oid)
      Create a new lock for the specified object.
      ObjectLock​(OID oid, java.lang.Object[] object, long version)  
    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      (package private) void acquireCreateLock​(TransactionContext tx)  
      (package private) void acquireLoadLock​(TransactionContext tx, boolean write, int timeout)  
      (package private) void acquireUpdateLock​(TransactionContext tx, int timeout)  
      (package private) void confirm​(TransactionContext tx, boolean succeed)  
      (package private) void delete​(TransactionContext tx)
      Informs the lock that the object has been deleted by the transaction holding the write lock.
      (package private) void enter()
      Indicate that a transaction is interested in this lock.
      void expire()
      Indicate that object needs to be expired from the cache.
      void expired()
      Indicate that object has been removed from the cache.
      java.lang.Object[] getObject()  
      java.lang.Object[] getObject​(TransactionContext tx)
      Get the object from the DespositBox, only the transaction have the read or write lock can get it.
      OID getOID()
      Return the object's OID.
      long getVersion()  
      (package private) boolean hasLock​(TransactionContext tx, boolean write)
      Returns true if the transaction holds a read or write lock on the object.
      (package private) void invalidate​(TransactionContext tx)  
      (package private) boolean isDisposable()
      Return true if this object can be safely disposed.
      (package private) boolean isEntered()
      Return true if there is any transaction called enter(), but not yet called leave().
      (package private) boolean isExclusivelyOwned​(TransactionContext tx)  
      (package private) boolean isExpired()
      Return true if this entry has been expired from the cache.
      (package private) boolean isFree()
      Return true if and only if this lock can be safely disposed.
      (package private) void leave()
      Indicate that a transaction is not interested to change the state of this lock anymore.
      (package private) void release​(TransactionContext tx)
      Releases a lock on the object previously acquired.
      void setObject​(TransactionContext tx, java.lang.Object[] object, long version)
      Set an object into the DespositBox, only a transaction has the write lock may call it method or IllegalArgumentException will be thrown.
      (package private) void setOID​(OID oid)
      Set OID of this lock to new value.
      void setVersion​(long version)
      Sets the new version of this object.
      java.lang.String toString()  
      (package private) void upgrade​(TransactionContext tx, int timeout)
      Acquires a lock on the object on behalf of the specified transaction.
      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
    • Constructor Detail

      • ObjectLock

        public ObjectLock​(OID oid)
        Create a new lock for the specified object. Must not create two locks for the same object. This will be the object returned from a successful call to one of the acquire.
        Parameters:
        oid - The object to create a lock for
      • ObjectLock

        public ObjectLock​(OID oid,
                          java.lang.Object[] object,
                          long version)
    • Method Detail

      • getOID

        public OID getOID()
        Return the object's OID.
        Specified by:
        getOID in interface DepositBox
        Returns:
        the object's OID.
      • setOID

        void setOID​(OID oid)
        Set OID of this lock to new value.
      • enter

        void enter()
        Indicate that a transaction is interested in this lock. A transaction should call this method if it is going to change the state of this lock (by calling acquire, update or relase.) It method should be synchronized externally to avoid race condition. enter and leave should be called exactly the same number of time.
      • leave

        void leave()
        Indicate that a transaction is not interested to change the state of this lock anymore. (ie, will not call either acquire update, release or delete.) It method should be synchronized externally.
      • isEntered

        boolean isEntered()
        Return true if there is any transaction called enter(), but not yet called leave().
      • isDisposable

        boolean isDisposable()
        Return true if this object can be safely disposed. An ObjectLock can be safely disposed if and only if the no transaction is holding any lock, nor any transaction isEntered.
      • hasLock

        boolean hasLock​(TransactionContext tx,
                        boolean write)
        Returns true if the transaction holds a read or write lock on the object. This method is an efficient mean to determine whether a lock is required, or if the object is owned by the transaction.
        Parameters:
        tx - The transaction
        write - True if must have a write lock
        Returns:
        True if the transaction has a lock on this object
      • isFree

        boolean isFree()
        Return true if and only if this lock can be safely disposed.
        Returns:
        True if no lock and no waiting.
      • isExpired

        boolean isExpired()
        Return true if this entry has been expired from the cache.
      • getObject

        public java.lang.Object[] getObject()
      • expire

        public void expire()
        Indicate that object needs to be expired from the cache.
      • expired

        public void expired()
        Indicate that object has been removed from the cache. Perform any post expiration cleanup. In particular, remove the reference to any saved cached objects.
      • setObject

        public void setObject​(TransactionContext tx,
                              java.lang.Object[] object,
                              long version)
        Description copied from interface: DepositBox
        Set an object into the DespositBox, only a transaction has the write lock may call it method or IllegalArgumentException will be thrown.
        Specified by:
        setObject in interface DepositBox
        Parameters:
        tx - the transaction in action
        object - to be store into deposit box
        version - of the object to be stored
      • getObject

        public java.lang.Object[] getObject​(TransactionContext tx)
        Description copied from interface: DepositBox
        Get the object from the DespositBox, only the transaction have the read or write lock can get it.
        Specified by:
        getObject in interface DepositBox
        Parameters:
        tx - the transaction in action
        Returns:
        An object instance.
      • getVersion

        public long getVersion()
        Specified by:
        getVersion in interface DepositBox
        Returns:
        the version (a timestamp) of the last setObject(object) call.
      • setVersion

        public void setVersion​(long version)
        Description copied from interface: DepositBox
        Sets the new version of this object.
        Specified by:
        setVersion in interface DepositBox
        Parameters:
        version - a timestamp.
      • upgrade

        void upgrade​(TransactionContext tx,
                     int timeout)
              throws LockNotGrantedException
        Acquires a lock on the object on behalf of the specified transaction. A write lock will be acquired only if there are no read/write locks on the object; only one write lock may be in effect. A read lock will be acquired only if there is no write lock on the object; multiple read locks are allowed. If the lock cannot be acquired immediately, the thread will block until the lock is made available or the timeout has elapsed. If the timeout has elapsed or a dead lock has been detected, a LockNotGrantedException is thrown. If the object has been deleted while waiting for a lock, a ObjectDeletedException is thrown. To prevent dead locks, a transaction must only call this method for any given object from a single thread and must mark the lock it is trying to acquire and return it from a call to TransactionContext.getWaitOnLock() if the call to this method has not returned yet. If a read lock is available for the transaction and a write lock is requested, the read lock is cancelled whether or not the write is acquired.
        Parameters:
        tx - The transaction requesting the lock
        timeout - Timeout waiting to acquire lock (in milliseconds), zero for no waiting
        Throws:
        LockNotGrantedException - Lock could not be granted in the specified timeout or a dead lock has been detected
        ObjectDeletedWaitingForLockException - The object has been deleted while waiting for the lock
      • release

        void release​(TransactionContext tx)
        Releases a lock on the object previously acquired. A write lock cannot be downgraded into a read lock and the transaction loses its lock on the object. Other transactions are allowed to acquire a read/write lock on the object.
        Parameters:
        tx - The transaction that holds the lock
      • delete

        void delete​(TransactionContext tx)
        Informs the lock that the object has been deleted by the transaction holding the write lock. The lock on the object is released and all transactions waiting for a lock will terminate with an ObjectDeletedException.
        Parameters:
        tx - The transaction that holds the lock
        Throws:
        java.lang.RuntimeException - Attempt to delete object without acquiring a write lock
      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object