Class ConcurrentLockSet.Entry

java.lang.Object
org.apache.derby.impl.services.locks.ConcurrentLockSet.Entry
Enclosing class:
ConcurrentLockSet

private static final class ConcurrentLockSet.Entry extends Object
Class representing an entry in the lock table.
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    (package private) Control
    The lock control.
    private Condition
    Condition variable which prevents calls to lock() from locking the entry.
    private final ReentrantLock
    Mutex used to ensure single-threaded access to the LockControls.
  • Constructor Summary

    Constructors
    Modifier
    Constructor
    Description
    private
     
  • Method Summary

    Modifier and Type
    Method
    Description
    (package private) void
    Notify that the lock request that is currently accessing the entry will be entering deadlock detection.
    (package private) void
    Notify that the deadlock detection triggered by the current thread has finished.
    (package private) void
    Lock the entry, ensuring exclusive access to the contained Control object.
    (package private) void
    Lock the entry while performing deadlock detection.
    (package private) void
    Unlock the entry, allowing other threads to lock and access the contained Control object.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • control

      Control control
      The lock control.
    • mutex

      private final ReentrantLock mutex
      Mutex used to ensure single-threaded access to the LockControls. To avoid Java deadlocks, no thread should ever hold the mutex of more than one entry. Excepted from this requirement is a thread which performs deadlock detection. During deadlock detection, a thread might hold several mutexes, but it is not allowed to hold any mutex when entering the deadlock detection. Only one thread is allowed to perform deadlock detection at a time.
    • deadlockDetection

      private Condition deadlockDetection
      Condition variable which prevents calls to lock() from locking the entry. If it is not null, only the thread performing deadlock detection may lock the entry (by calling lockForDeadlockDetection()).
  • Constructor Details

    • Entry

      private Entry()
  • Method Details

    • lock

      void lock()
      Lock the entry, ensuring exclusive access to the contained Control object. The call will block until the entry can be locked. If the entry is unlocked and deadlockDetection is not null, the entry belongs to a thread which waits for deadlock detection to be initiated, and the call will block until that thread has finished its deadlock detection.
    • unlock

      void unlock()
      Unlock the entry, allowing other threads to lock and access the contained Control object.
    • lockForDeadlockDetection

      void lockForDeadlockDetection()
      Lock the entry while performing deadlock detection. This method will lock the entry even when deadlockDetection is not null. If deadlockDetection is not null, we know the entry and its Control will not be accessed by others until we have finished the deadlock detection, so it's OK for us to access it.
    • enterDeadlockDetection

      void enterDeadlockDetection()
      Notify that the lock request that is currently accessing the entry will be entering deadlock detection. Unlock the entry to allow the current thread or other threads to lock the entry for deadlock detection, but set the condition variable to prevent regular locking of the entry.
    • exitDeadlockDetection

      void exitDeadlockDetection()
      Notify that the deadlock detection triggered by the current thread has finished. Re-lock the entry and notify any waiters that the deadlock detection has completed.