org.apache.derby.impl.services.locks
Class ConcurrentLockSet

java.lang.Object
  extended by org.apache.derby.impl.services.locks.ConcurrentLockSet
All Implemented Interfaces:
LockTable

final class ConcurrentLockSet
extends java.lang.Object
implements LockTable

A ConcurrentLockSet is a complete lock table which maps Lockables to LockControl objects.

A LockControl contains information about the locks held on a Lockable.
MT - Mutable : All public methods of this class, except addWaiters, are thread safe. addWaiters can only be called from the thread which performs deadlock detection. Only one thread can perform deadlock detection at a time.
The class creates ActiveLock and LockControl objects. LockControl objects are never passed out of this class, All the methods of LockControl are called while holding a ReentrantLock associated with the Lockable controlled by the LockControl, thus providing the single threading that LockControl required. Methods of Lockables are only called by this class or LockControl, and always while holding the corresponding ReentrantLock, thus providing the single threading that Lockable requires.

See Also:
LockControl

Nested Class Summary
private static class ConcurrentLockSet.Entry
          Class representing an entry in the lock table.
 
Field Summary
private  java.util.concurrent.atomic.AtomicInteger blockCount
           
private  int deadlockTimeout
          Timeout for deadlocks, in ms.
private  boolean deadlockTrace
           
private  AbstractPool factory
           
private  java.util.concurrent.ConcurrentHashMap<Lockable,ConcurrentLockSet.Entry> locks
          Hash table which maps Lockable objects to Locks.
private  java.util.ArrayList<ConcurrentLockSet.Entry> seenByDeadlockDetection
          List containing all entries seen by the last call to addWaiters().
private  int waitTimeout
           
 
Constructor Summary
ConcurrentLockSet(AbstractPool factory)
           
 
Method Summary
 void addWaiters(java.util.Map waiters)
          Add all waiters in this lock table to a Map object.
 boolean anyoneBlocked()
          Check whether anyone is blocked.
private  java.lang.Object[] checkDeadlock(ConcurrentLockSet.Entry entry, ActiveLock waitingLock, byte wakeupReason)
          Check whether there is a deadlock.
private  ConcurrentLockSet.Entry getEntry(Lockable ref)
          Get an entry from the lock table.
 int getWaitTimeout()
          Get the wait timeout in milliseconds.
 Lock lockObject(CompatibilitySpace compatibilitySpace, Lockable ref, java.lang.Object qualifier, int timeout)
          Lock an object within a specific compatibility space.
 void oneLessWaiter()
          Decrease blockCount by one.
 void oneMoreWaiter()
          Increase blockCount by one.
 void setDeadlockTimeout(int timeout)
          Set the deadlock timeout.
 void setDeadlockTrace(boolean val)
          Enable or disable tracing of deadlocks.
 void setWaitTimeout(int timeout)
          Set the wait timeout.
 java.util.Map<Lockable,Control> shallowClone()
          make a shallow clone of myself and my lock controls
private  java.lang.String toDebugString()
           
private  void unlock(ConcurrentLockSet.Entry entry, Latch item, int unlockCount)
          Unlock an object, previously locked by lockObject().
 void unlock(Latch item, int unlockCount)
          Unlock an object, previously locked by lockObject().
 Lock unlockReference(CompatibilitySpace space, Lockable ref, java.lang.Object qualifier, java.util.Map group)
          Unlock an object once if it is present in the specified group.
 boolean zeroDurationLockObject(CompatibilitySpace space, Lockable ref, java.lang.Object qualifier, int timeout)
          Lock an object and release the lock immediately.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

factory

private final AbstractPool factory

locks

private final java.util.concurrent.ConcurrentHashMap<Lockable,ConcurrentLockSet.Entry> locks
Hash table which maps Lockable objects to Locks.


seenByDeadlockDetection

private java.util.ArrayList<ConcurrentLockSet.Entry> seenByDeadlockDetection
List containing all entries seen by the last call to addWaiters(). Makes it possible for the deadlock detection thread to lock all the entries it has visited until it has finished. This prevents false deadlocks from being reported (because all observed waiters must still be waiting when the deadlock detection has completed).


deadlockTimeout

private int deadlockTimeout
Timeout for deadlocks, in ms.
MT - immutable


waitTimeout

private int waitTimeout

deadlockTrace

private boolean deadlockTrace

blockCount

private final java.util.concurrent.atomic.AtomicInteger blockCount
Constructor Detail

ConcurrentLockSet

ConcurrentLockSet(AbstractPool factory)
Method Detail

getEntry

private ConcurrentLockSet.Entry getEntry(Lockable ref)
Get an entry from the lock table. If no entry exists for the Lockable, insert an entry. The returned entry will be locked and is guaranteed to still be present in the table.

Parameters:
ref - the Lockable whose entry to return
Returns:
the entry for the Lockable, locked for exclusive access

checkDeadlock

private java.lang.Object[] checkDeadlock(ConcurrentLockSet.Entry entry,
                                         ActiveLock waitingLock,
                                         byte wakeupReason)
Check whether there is a deadlock. Make sure that only one thread enters deadlock detection at a time.

Parameters:
entry - the entry in the lock table for the lock request that triggered deadlock detection
waitingLock - the waiting lock
wakeupReason - the reason for waking up the waiter
Returns:
an object describing the deadlock

lockObject

public Lock lockObject(CompatibilitySpace compatibilitySpace,
                       Lockable ref,
                       java.lang.Object qualifier,
                       int timeout)
                throws StandardException
Lock an object within a specific compatibility space.

Specified by:
lockObject in interface LockTable
Parameters:
compatibilitySpace - Compatibility space.
ref - Lockable reference.
qualifier - Qualifier.
timeout - Timeout in milli-seconds
Returns:
Object that represents the lock.
Throws:
StandardException - Standard Derby policy.

unlock

public void unlock(Latch item,
                   int unlockCount)
Unlock an object, previously locked by lockObject(). If unlockCOunt is not zero then the lock will be unlocked that many times, otherwise the unlock count is taken from item.

Specified by:
unlock in interface LockTable
Parameters:
item - the lock to unlock
unlockCount - the number of times to unlock the item; or zero, meaning take the unlock count from the item

unlock

private void unlock(ConcurrentLockSet.Entry entry,
                    Latch item,
                    int unlockCount)
Unlock an object, previously locked by lockObject().

Parameters:
entry - the entry in which the lock is contained (the current thread must have locked the entry)
item - the item to unlock
unlockCount - the number of times to unlock the item (if zero, take the unlock count from item)

unlockReference

public Lock unlockReference(CompatibilitySpace space,
                            Lockable ref,
                            java.lang.Object qualifier,
                            java.util.Map group)
Unlock an object once if it is present in the specified group. Also remove the object from the group.

Specified by:
unlockReference in interface LockTable
Parameters:
space - the compatibility space
ref - a reference to the locked object
qualifier - qualifier of the lock
group - a map representing the locks in a group
Returns:
the corresponding lock in the group map, or null if the object was not unlocked

zeroDurationLockObject

public boolean zeroDurationLockObject(CompatibilitySpace space,
                                      Lockable ref,
                                      java.lang.Object qualifier,
                                      int timeout)
                               throws StandardException
Lock an object and release the lock immediately. Equivalent to
 Lock lock = lockTable.lockObject(space, ref, qualifier, timeout);
 lockTable.unlock(lock, 1);
 
except that the implementation might be more efficient.

Specified by:
zeroDurationLockObject in interface LockTable
Parameters:
space - the compatibility space
ref - a reference to the locked object
qualifier - qualifier of the lock
timeout - maximum time to wait in milliseconds (C_LockFactory.NO_WAIT means don't wait)
Returns:
true if the object was locked, or false if the object couldn't be locked immediately and timeout was NO_WAIT or LockOwner had the noWait flag set
Throws:
StandardException - if the lock could not be obtained

setDeadlockTimeout

public void setDeadlockTimeout(int timeout)
Set the deadlock timeout.

Specified by:
setDeadlockTimeout in interface LockTable
Parameters:
timeout - deadlock timeout in milliseconds

setWaitTimeout

public void setWaitTimeout(int timeout)
Set the wait timeout.

Specified by:
setWaitTimeout in interface LockTable
Parameters:
timeout - wait timeout in milliseconds

getWaitTimeout

public int getWaitTimeout()
Get the wait timeout in milliseconds.

Specified by:
getWaitTimeout in interface LockTable

setDeadlockTrace

public void setDeadlockTrace(boolean val)
Description copied from interface: LockTable
Enable or disable tracing of deadlocks.

Specified by:
setDeadlockTrace in interface LockTable
Parameters:
val - true enables tracing, false disables tracing

toDebugString

private java.lang.String toDebugString()

addWaiters

public void addWaiters(java.util.Map waiters)
Add all waiters in this lock table to a Map object. This method can only be called by the thread that is currently performing deadlock detection. All entries that are visited in the lock table will be locked when this method returns. The entries that have been seen and locked will be unlocked after the deadlock detection has finished.

Specified by:
addWaiters in interface LockTable
Parameters:
waiters - the map to add the waiters to
See Also:
LockControl.addWaiters(java.util.Map)

shallowClone

public java.util.Map<Lockable,Control> shallowClone()
make a shallow clone of myself and my lock controls

Specified by:
shallowClone in interface LockTable
Returns:
a shallow clone of the lock table

oneMoreWaiter

public void oneMoreWaiter()
Increase blockCount by one.

Specified by:
oneMoreWaiter in interface LockTable

oneLessWaiter

public void oneLessWaiter()
Decrease blockCount by one.

Specified by:
oneLessWaiter in interface LockTable

anyoneBlocked

public boolean anyoneBlocked()
Check whether anyone is blocked.

Specified by:
anyoneBlocked in interface LockTable
Returns:
true if someone is blocked, false otherwise

Built on Thu 2010-12-23 20:49:13+0000, from revision ???

Apache Derby V10.6 Internals - Copyright © 2004,2007 The Apache Software Foundation. All Rights Reserved.