Package org.apache.ignite

Interface IgniteLock

  • All Superinterfaces:
    AutoCloseable, Closeable, Lock
    public interface IgniteLock
extends Lock, Closeable
    This interface provides a rich API for working with distributed reentrant locks.

    Functionality

    Distributed reentrant lock provides functionality similar to java.util.concurrent.ReentrantLock.

    Creating Distributed ReentrantLock

    Instance of cache reentrant lock can be created by calling the following method: Ignite.reentrantLock(String, boolean, boolean, boolean).

    Protection from failover

    Ignite lock can automatically recover from node failure.
    • If failoverSafe flag is set to true upon creation, in case a node owning the lock fails, lock will be automatically released and become available for threads on other nodes to acquire. No exception will be thrown.
    • If failoverSafe flag is set to false upon creation, in case a node owning the lock fails, IgniteException will be thrown on every other node attempting to perform any operation on this lock. No automatic recovery will be attempted, and lock will be marked as broken (i.e. unusable), which can be checked using the method #isBroken(). Broken lock cannot be reused again.

    Implementation issues

    Ignite lock comes in two flavours: fair and non-fair. Non-fair lock assumes no ordering should be imposed on acquiring threads; in case of contention, threads from all nodes compete for the lock once the lock is released. In most cases this is the desired behaviour. However, in some cases, using the non-fair lock can lead to uneven load distribution among nodes. Fair lock solves this issue by imposing strict FIFO ordering policy at a cost of an additional transaction. This ordering does not guarantee fairness of thread scheduling (similar to java.util.concurrent.ReentrantLock). Thus, one of many threads on any node using a fair lock may obtain it multiple times in succession while other active threads are not progressing and not currently holding the lock. Also note that the untimed tryLock method does not honor the fairness setting. It will succeed if the lock is available even if other threads are waiting.

    As a rule of thumb, whenever there is a reasonable time window between successive calls to release and acquire the lock, non-fair lock should be preferred: 
     
      while(someCondition){
          // do anything
          lock.lock();
          try{
              // ...
          }
          finally {
              lock.unlock();
          }
      }
    If successive calls to release/acquire are following immediately, e.g. 
     
      while(someCondition){
          lock.lock();
          try {
              // do something
          }
          finally {
              lock.unlock();
          }
      }
    using the fair lock is reasonable in order to allow even distribution of load among nodes (although overall throughput may be lower due to increased overhead).

    • Method Detail

      • name

        String name()
        Name of atomic reentrant lock.
        Returns:
        Name of atomic reentrant lock.

      • lock

        void lock()
   throws IgniteException
        Acquires the distributed reentrant lock.

        Acquires the lock if it is not held by another thread and returns immediately, setting the lock hold count to one.

        If the current thread already holds this lock then the hold count is incremented by one and the method returns immediately.

        If the lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:

        • The lock is acquired by the current thread; or
        • Lock is broken (any node failed while owning this lock), and lock is created in non-failoverSafe mode.
        • Local node is stopped.
        Specified by:
        lock in interface Lock
        Throws:
        IgniteException - if the node is stopped or broken in non-failoverSafe mode

      • lockInterruptibly

        void lockInterruptibly()
                throws IgniteInterruptedException,
                       IgniteException
        Acquires the lock unless the current thread is interrupted.

        Acquires the lock if it is not held by another thread and returns immediately, setting the lock hold count to one.

        If the current thread already holds this lock then the hold count is incremented by one and the method returns immediately.

        If the lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of four things happens:

        • The lock is acquired by the current thread; or
        • Some other thread interrupts the current thread.
        • Lock is broken (any node failed while owning this lock), and lock is created in non-failoverSafe mode.
        • Local node is stopped.

        If the lock is acquired by the current thread then the lock hold count is set to one.

        If the current thread:

        • has its interrupted status set on entry to this method; or
        • is interrupted while acquiring the lock; or then IgniteInterruptedException is thrown and the current thread's interrupted status is cleared.

        IgniteException is thrown in case:

        • the lock is broken before or during the attempt to acquire this lock; or
        • local node is stopped,

        In this implementation, as this method is an explicit interruption point, preference is given to responding to the interrupt over normal or reentrant acquisition of the lock.

        Specified by:
        lockInterruptibly in interface Lock
        Throws:
        IgniteInterruptedException - if the current thread is interrupted
        IgniteException - if the lock is broken in non-failoverSafe mode (any node failed while owning this lock), or local node is stopped

      • tryLock

        boolean tryLock()
         throws IgniteException
        Acquires the lock only if it is free at the time of invocation.

        Acquires the lock if it is available and returns immediately with the value true. If the lock is not available then this method will return immediately with the value false.

        A typical usage idiom for this method would be: 

         
 Lock lock = ...;
 if (lock.tryLock()) {
   try {
     // manipulate protected state
   } finally {
     lock.unlock();
   }
 } else {
   // perform alternative actions
 }
        This usage ensures that the lock is unlocked if it was acquired, and doesn't try to unlock if the lock was not acquired. If node is stopped, or any node failed while owning the lock in non-failoverSafe mode, then IgniteException is thrown.
        Specified by:
        tryLock in interface Lock
        Returns:
        true if the lock was acquired and false otherwise
        Throws:
        IgniteException - if node is stopped, or lock is already broken in non-failover safe mode

      • tryLock

        boolean tryLock​(long timeout,
                TimeUnit unit)
         throws IgniteInterruptedException,
                IgniteException
        Acquires the lock if it is not held by another thread within the given waiting time and the current thread has not been interrupted.

        Acquires the lock if it is not held by another thread and returns immediately with the value true, setting the lock hold count to one.

        If the current thread already holds this lock then the hold count is incremented by one and the method returns true.

        If the lock is held by another thread then the current thread becomes disabled for thread scheduling purposes and lies dormant until one of five things happens:

        • The lock is acquired by the current thread; or
        • Some other thread interrupts the current thread; or
        • Lock is broken (any node failed while owning this lock), and lock is created in non-failoverSafe mode.
        • Local node is stopped.
        • The specified waiting time elapses

        If the lock is acquired then the value true is returned and the lock hold count is set to one.

        If the current thread:

        • has its interrupted status set on entry to this method; or
        • is interrupted while acquiring the lock; or
        then IgniteInterruptedException is thrown and the current thread's interrupted status is cleared.

        IgniteException is thrown in case:

        • the lock is broken before or during the attempt to acquire this lock; or
        • local node is stopped,

        If the specified waiting time elapses then the value false is returned. If the time is less than or equal to zero, the method will not wait at all.

        In this implementation, as this method is an explicit interruption point, preference is given to responding to the interrupt over normal or reentrant acquisition of the lock, and over reporting the elapse of the waiting time.

        Specified by:
        tryLock in interface Lock
        Parameters:
        timeout - the time to wait for the lock
        unit - the time unit of the timeout argument
        Returns:
        true if the lock was free and was acquired by the current thread, or the lock was already held by the current thread; and false if the waiting time elapsed before the lock could be acquired
        Throws:
        IgniteInterruptedException - if the current thread is interrupted
        IgniteException - if node is stopped, or lock is already broken in non-failover safe mode
        NullPointerException - if the time unit is null

      • getOrCreateCondition

        IgniteCondition getOrCreateCondition​(String name)
                              throws IgniteException
        Returns a Condition instance for use with this IgniteLock instance.
        • If this lock is not held when any of the Condition waiting or signalling methods are called, then an IllegalMonitorStateException is thrown.
        • When the condition waiting methods are called the lock is released and, before they return, the lock is reacquired and the lock hold count restored to what it was when the method was called.
        • If a thread is interrupted while waiting then the wait will terminate, an IgniteInterruptedException will be thrown, and the thread's interrupted status will be cleared.
        • Waiting threads are signalled in FIFO order.
        Parameters:
        name - Name of the distributed condition object
        Returns:
        the Condition object
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • getHoldCount

        int getHoldCount()
          throws IgniteException
        Queries the number of holds on this lock by the current thread.
        Returns:
        the number of holds on this lock by the current thread, or zero if this lock is not held by the current thread
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • isHeldByCurrentThread

        boolean isHeldByCurrentThread()
                       throws IgniteException
        Queries if this lock is held by the current thread.
        Returns:
        true if current thread holds this lock and false otherwise
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • isLocked

        boolean isLocked()
          throws IgniteException
        Queries if this lock is held by any thread on any node. This method is designed for use in monitoring of the system state, not for synchronization control.
        Returns:
        true if any thread on this or any other node holds this lock and false otherwise
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • hasQueuedThreads

        boolean hasQueuedThreads()
                  throws IgniteException
        Queries whether any threads on this node are waiting to acquire this lock. Note that because cancellations may occur at any time, a true return does not guarantee that any other thread will ever acquire this lock. This method is designed primarily for use in monitoring of the system state.
        Returns:
        true if there may be other threads on this node waiting to acquire the lock
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • hasQueuedThread

        boolean hasQueuedThread​(Thread thread)
                 throws IgniteException
        Queries whether the given thread is waiting to acquire this lock. Note that because cancellations may occur at any time, a true return does not guarantee that this thread will ever acquire this lock. This method is designed primarily for use in monitoring of the system state.
        Parameters:
        thread - the thread
        Returns:
        true if the given thread is queued waiting for this lock
        Throws:
        NullPointerException - if the thread is null
        IgniteException - if the lock is not initialized or already removed

      • hasWaiters

        boolean hasWaiters​(IgniteCondition condition)
            throws IgniteException
        Queries whether any threads on this node are waiting on the given condition associated with this lock. Note that because timeouts and interrupts may occur at any time, a true return does not guarantee that a future signal will awaken any threads. This method is designed primarily for use in monitoring of the system state.
        Parameters:
        condition - the condition
        Returns:
        true if there are any waiting threads on this node
        Throws:
        IllegalMonitorStateException - if this lock is not held
        IllegalArgumentException - if the given condition is not associated with this lock
        NullPointerException - if the condition is null
        IgniteException - if the lock is not initialized or already removed

      • getWaitQueueLength

        int getWaitQueueLength​(IgniteCondition condition)
                throws IgniteException
        Returns an estimate of the number of threads on this node that are waiting on the given condition associated with this lock. Note that because timeouts and interrupts may occur at any time, the estimate serves only as an upper bound on the actual number of waiters. This method is designed for use in monitoring of the system state, not for synchronization control.
        Parameters:
        condition - the condition
        Returns:
        the estimated number of waiting threads on this node
        Throws:
        IllegalMonitorStateException - if this lock is not held
        IllegalArgumentException - if the given condition is not associated with this lock
        NullPointerException - if the condition is null
        IgniteException - if the lock is not initialized or already removed

      • isFailoverSafe

        boolean isFailoverSafe()
        Returns true if this lock is safe to use after node failure. If not, IgniteInterruptedException is thrown on every other node after node failure.
        Returns:
        true if this reentrant lock has failoverSafe set true
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • isFair

        boolean isFair()
        Returns true if this lock is fair. Fairness flag can only be set on lock creation.
        Returns:
        true if this reentrant lock has fairness flag set true.
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • isBroken

        boolean isBroken()
          throws IgniteException
        Returns true if any node that owned the locked failed before releasing the lock.
        Returns:
        true if any node failed while owning the lock since the lock on this node was initialized.
        Throws:
        IgniteException - if the lock is not initialized or already removed

      • removed

        boolean removed()
        Gets status of reentrant lock.
        Returns:
        true if reentrant lock was removed from cache, false in other case.