arlut.csd.ganymede
Class DBWriteLock

java.lang.Object
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  +--arlut.csd.ganymede.DBLock
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        +--arlut.csd.ganymede.DBWriteLock

public class DBWriteLock

extends DBLock

A DBWriteLock is a DBLock subclass used to lock one or more DBObjectBases for the purposes of committing changes into those bases, preventing any other threads from reading or writing to the database while the update is being performed. When a DBWriteLock is established on a DBObjectBase, the establishing thread suspends until all readers currently working in the specified DBObjectBases complete. The write lock is then established, and the thread possessing the DBWriteLock is free to replace objects in the DBStore with modified copies.

DBWriteLocks are typically created and managed by the code in the DBEditSet class. It is very important that any thread that obtains a DBWriteLock be scrupulous about releasing the lock in a timely fashion once the appropriate changes are made in the database.

See Also:

DBEditSet, DBObjectBase

Field Summary

(package private) static boolean

debug

Fields inherited from class arlut.csd.ganymede.DBLock

abort, baseSet, inEstablish, key, locked, lockSync

Constructor Summary

DBWriteLock(arlut.csd.ganymede.DBStore store)
constructor to get a write lock on all the object bases

DBWriteLock(arlut.csd.ganymede.DBStore store, java.util.Vector baseSet)
constructor to get a write lock on a subset of the object bases.

Method Summary

void	abort() Withdraw this lock.
void	establish(java.lang.Object key) Establish a dump lock on bases specified in this DBWriteLock's constructor.
void	release() Release this lock on all bases locked

Methods inherited from class arlut.csd.ganymede.DBLock

getKey, isLocked, isLocked, isLocked, overlaps, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

debug

static final boolean debug

See Also:

Constant Field Values

Constructor Detail

DBWriteLock

public DBWriteLock(arlut.csd.ganymede.DBStore store)

constructor to get a write lock on all the object bases

DBWriteLock

public DBWriteLock(arlut.csd.ganymede.DBStore store,
                   java.util.Vector baseSet)

constructor to get a write lock on a subset of the object bases.

Method Detail

establish

public void establish(java.lang.Object key)
               throws java.lang.InterruptedException

Establish a dump lock on bases specified in this DBWriteLock's constructor. Can throw InterruptedException if another thread orders us to abort() while we're waiting for permission to proceed with writes on the specified baseset.

Specified by:

establish in class DBLock

java.lang.InterruptedException

release

public void release()

Release this lock on all bases locked

Specified by:

release in class DBLock

abort

public void abort()

Withdraw this lock. This method can be called by a thread to interrupt a lock establish that is blocked waiting to get access to the appropriate set of DBObjectBase objects. If this method is called while another thread is blocked in establish(), establish() will throw an InterruptedException.

Once abort() is processed, this lock may never be established. Any subsequent calls to estabish() will always throw InterruptedException.

Specified by:

abort in class DBLock