Class ConcurrentLockSet

java.lang.Object
org.apache.derby.impl.services.locks.ConcurrentLockSet
All Implemented Interfaces:
LockTable
final class ConcurrentLockSet extends 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:

  • Field Details

    • factory

      private final AbstractPool factory

    • locks

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

    • seenByDeadlockDetection

      private 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 AtomicInteger blockCount

  • Constructor Details

    • ConcurrentLockSet

      ConcurrentLockSet(AbstractPool factory)

  • Method Details

    • 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 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, 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, Object qualifier, 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, 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 String toDebugString()

    • addWaiters

      public void addWaiters(Map<Object,Object> 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:

    • shallowClone

      public 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