Package org.apache.derby.impl.services.locks

Class ConcurrentLockSet.Entry

  • Enclosing class:
    ConcurrentLockSet
    private static final class ConcurrentLockSet.Entry
extends java.lang.Object
    Class representing an entry in the lock table.

    • Field Summary

      Fields 
      Modifier and Type Field Description
      (package private) Control control
      The lock control.
      private java.util.concurrent.locks.Condition deadlockDetection
      Condition variable which prevents calls to lock() from locking the entry.
      private java.util.concurrent.locks.ReentrantLock mutex
      Mutex used to ensure single-threaded access to the LockControls.

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      private Entry()  

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      (package private) void enterDeadlockDetection()
      Notify that the lock request that is currently accessing the entry will be entering deadlock detection.
      (package private) void exitDeadlockDetection()
      Notify that the deadlock detection triggered by the current thread has finished.
      (package private) void lock()
      Lock the entry, ensuring exclusive access to the contained Control object.
      (package private) void lockForDeadlockDetection()
      Lock the entry while performing deadlock detection.
      (package private) void unlock()
      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 Detail

      • control

        Control control
        The lock control.

      • mutex

        private final java.util.concurrent.locks.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 java.util.concurrent.locks.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 Detail

      • Entry

        private Entry()

    • Method Detail

      • 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.