ReentrantLock (Drools 4.0.0.11754MR2 API) - JBoss RULES 4.0.0.11754MR2 API 英文版文档

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org.drools.util.concurrent.locks
Class ReentrantLock

java.lang.Object
  org.drools.util.concurrent.locks.ReentrantLock

All Implemented Interfaces:: Serializable, Lock

public class ReentrantLock
extends Object
implements Lock, Serializable
extends Object
implements Lock, Serializable

This is a stripped down version of jdk1.5 ReentrantLock. All the condition and wait stuff has been removed

Since:: 1.5
Author:: Doug Lea, Dawid Kurzyniec
See Also:: Serialized Form

Constructor Summary

ReentrantLock()
          Creates an instance of ReentrantLock.

Method Summary

int getHoldCount()
          Queries the number of holds on this lock by the current thread.

protected Thread getOwner()
          null if not owned.

protected Collection getQueuedThreads()
          Returns a collection containing threads that may be waiting to acquire this lock.

int getQueueLength()
          Returns an estimate of the number of threads waiting to acquire this lock.

boolean hasQueuedThread(Thread thread)
          Queries whether the given thread is waiting to acquire this lock.

boolean hasQueuedThreads()
          Queries whether any threads are waiting to acquire this lock.

boolean isHeldByCurrentThread()
          Queries if this lock is held by the current thread.

boolean isLocked()
          Queries if this lock is held by any thread.

void lock()
          Acquires the lock.

void lockInterruptibly()
          Acquires the lock unless the current thread is interrupted.

String toString()
          Returns a string identifying this lock, as well as its lock state.

boolean tryLock()
          Acquires the lock only if it is not held by another thread at the time of invocation.

void unlock()
          Attempts to release this lock.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Summary
`ReentrantLock()` Creates an instance of `ReentrantLock`.

Method Summary
`int`	`getHoldCount()` Queries the number of holds on this lock by the current thread.
`protected Thread`	`getOwner()` `null` if not owned.
`protected Collection`	`getQueuedThreads()` Returns a collection containing threads that may be waiting to acquire this lock.
`int`	`getQueueLength()` Returns an estimate of the number of threads waiting to acquire this lock.
`boolean`	`hasQueuedThread(Thread thread)` Queries whether the given thread is waiting to acquire this lock.
`boolean`	`hasQueuedThreads()` Queries whether any threads are waiting to acquire this lock.
`boolean`	`isHeldByCurrentThread()` Queries if this lock is held by the current thread.
`boolean`	`isLocked()` Queries if this lock is held by any thread.
`void`	`lock()` Acquires the lock.
`void`	`lockInterruptibly()` Acquires the lock unless the current thread is `interrupted`.
`String`	`toString()` Returns a string identifying this lock, as well as its lock state.
`boolean`	`tryLock()` Acquires the lock only if it is not held by another thread at the time of invocation.
`void`	`unlock()` Attempts to release this lock.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

Constructor Detail

ReentrantLock

public ReentrantLock()

Creates an instance of ReentrantLock. This is equivalent to using ReentrantLock(false).

Method Detail

lock

public void lock()

Acquires the 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 the 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 the lock has been acquired, at which time the lock hold count is set to one.

Specified by:: lock in interface Lock

lockInterruptibly

public void lockInterruptibly()
                       throws InterruptedException

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 two things happens:

The lock is acquired by the current thread; or
Some other thread interrupts the current thread.

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,

then InterruptedException is thrown and the current thread's interrupted status is cleared.

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:: InterruptedException - if the current thread is interrupted
See Also:: Thread.interrupt()

tryLock

public boolean tryLock()

Acquires the lock only if it is not held by another thread at the time of invocation.

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. Even when this lock has been set to use a fair ordering policy, a call to tryLock() will immediately acquire the lock if it is available, whether or not other threads are currently waiting for the lock. This "barging" behavior can be useful in certain circumstances, even though it breaks fairness. If you want to honor the fairness setting for this lock, then use tryLock(0, TimeUnit.SECONDS) which is almost equivalent (it also detects interruption).

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 this method will return immediately with the value false.

Specified by:: tryLock in interface Lock

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 otherwise.

unlock

public void unlock()

Attempts to release this lock.

If the current thread is the holder of this lock then the hold count is decremented. If the hold count is now zero then the lock is released. If the current thread is not the holder of this lock then IllegalMonitorStateException is thrown.

Specified by:: unlock in interface Lock

Throws:: IllegalMonitorStateException - if the current thread does not hold this lock.

getHoldCount

public int getHoldCount()

Queries the number of holds on this lock by the current thread.

A thread has a hold on a lock for each lock action that is not matched by an unlock action.

The hold count information is typically only used for testing and debugging purposes. For example, if a certain section of code should not be entered with the lock already held then we can assert that fact:

 class X {
   ReentrantLock lock = new ReentrantLock();
   // ...
   public void m() {
     assert lock.getHoldCount() == 0;
     lock.lock();
     try {
       // ... method body
     } finally {
       lock.unlock();
     }
   }
 }

Returns:: the number of holds on this lock by the current thread, or zero if this lock is not held by the current thread.

isHeldByCurrentThread

public boolean isHeldByCurrentThread()

Queries if this lock is held by the current thread.

Analogous to the Thread.holdsLock(java.lang.Object) method for built-in monitor locks, this method is typically used for debugging and testing. For example, a method that should only be called while a lock is held can assert that this is the case:

 class X {
   ReentrantLock lock = new ReentrantLock();
   // ...

   public void m() {
       assert lock.isHeldByCurrentThread();
       // ... method body
   }
 }

It can also be used to ensure that a reentrant lock is used in a non-reentrant manner, for example:

 class X {
   ReentrantLock lock = new ReentrantLock();
   // ...

   public void m() {
       assert !lock.isHeldByCurrentThread();
       lock.lock();
       try {
           // ... method body
       } finally {
           lock.unlock();
       }
   }
 }

Returns:: true if current thread holds this lock and false otherwise.

isLocked

public boolean isLocked()

Queries if this lock is held by any thread. This method is designed for use in monitoring of the system state, not for synchronization control.

Returns:: true if any thread holds this lock and false otherwise.

getOwner

protected Thread getOwner()

null if not owned. When this method is called by a thread that is not the owner, the return value reflects a best-effort approximation of current lock status. For example, the owner may be momentarily null even if there are threads trying to acquire the lock but have not yet done so. This method is designed to facilitate construction of subclasses that provide more extensive lock monitoring facilities.

Returns:: the owner, or null if not owned

hasQueuedThreads

public final boolean hasQueuedThreads()

Queries whether any threads 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 waiting to acquire the lock.

hasQueuedThread

public final boolean hasQueuedThread(Thread thread)

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 thread is null

getQueueLength

public final int getQueueLength()

Returns an estimate of the number of threads waiting to acquire this lock. The value is only an estimate because the number of threads may change dynamically while this method traverses internal data structures. This method is designed for use in monitoring of the system state, not for synchronization control.

Returns:: the estimated number of threads waiting for this lock

getQueuedThreads

protected Collection getQueuedThreads()

Returns a collection containing threads that may be waiting to acquire this lock. Because the actual set of threads may change dynamically while constructing this result, the returned collection is only a best-effort estimate. The elements of the returned collection are in no particular order. This method is designed to facilitate construction of subclasses that provide more extensive monitoring facilities.

Returns:: the collection of threads

toString

public String toString()

Returns a string identifying this lock, as well as its lock state. The state, in brackets, includes either the String "Unlocked" or the String "Locked by" followed by the Thread.getName() of the owning thread.

Overrides:: toString in class Object

Returns:: a string identifying this lock, as well as its lock state.