java.util.concurrent.atomic.AtomicReferenceFieldUpdater#get()源码实例Demo

/**
 * There are some scenarios where a completion {@link TerminalNotification} can be overridden with an error if
 * errors are produced asynchronously.
 * <p>
 * This method helps set {@link TerminalNotification} atomically providing such an override.
 *
 * @param toSet {@link TerminalNotification} to set.
 * @param overrideComplete Whether exisiting {@link TerminalNotification#complete()} should be overridden with the
 * {@code toSet}.
 * @param terminalNotificationUpdater {@link AtomicReferenceFieldUpdater} to access the current
 * {@link TerminalNotification}.
 * @param flagOwner instance of {@link R} that owns the current {@link TerminalNotification} field referenced by
 * {@code terminalNotificationUpdater}.
 * @param <R> Type of {@code flagOwner}.
 * @return {@code true} if {@code toSet} is updated as the current {@link TerminalNotification}.
 */
public static <R> boolean trySetTerminal(TerminalNotification toSet, boolean overrideComplete,
                 AtomicReferenceFieldUpdater<R, TerminalNotification> terminalNotificationUpdater, R flagOwner) {
    for (;;) {
        TerminalNotification curr = terminalNotificationUpdater.get(flagOwner);
        if (curr != null && !overrideComplete) {
            // Once terminated, terminalNotification will never be set back to null.
            return false;
        } else if (curr == null && terminalNotificationUpdater.compareAndSet(flagOwner, null, toSet)) {
            return true;
        } else if (curr != null && curr.cause() == null) {
            // Override complete
            if (terminalNotificationUpdater.compareAndSet(flagOwner, curr, toSet)) {
                return true;
            }
        } else {
            return false;
        }
    }
}
 

/**
 * Atomically set the field to a {@link Disposable} and dispose the old content.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @param newValue the new Disposable to set
 * @return true if successful, false if the field contains the {@link #DISPOSED} instance.
 */
static <T> boolean set(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder, @Nullable Disposable newValue) {
	for (;;) {
		Disposable current = updater.get(holder);
		if (current == DISPOSED) {
			if (newValue != null) {
				newValue.dispose();
			}
			return false;
		}
		if (updater.compareAndSet(holder, current, newValue)) {
			if (current != null) {
				current.dispose();
			}
			return true;
		}
	}
}
 

/**
 * Atomically set the field to a {@link Disposable} and dispose the old content.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @param newValue the new Disposable to set
 * @return true if successful, false if the field contains the {@link #DISPOSED} instance.
 */
public static <T> boolean set(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder, @Nullable Disposable newValue) {
	for (;;) {
		Disposable current = updater.get(holder);
		if (current == DISPOSED) {
			if (newValue != null) {
				newValue.dispose();
			}
			return false;
		}
		if (updater.compareAndSet(holder, current, newValue)) {
			if (current != null) {
				current.dispose();
			}
			return true;
		}
	}
}
 

/**
 * A generic utility to atomically replace a subscription or cancel the replacement
 * if current subscription is marked as cancelled (as in {@link #cancelledSubscription()})
 * or was concurrently updated before.
 * <p>
 * The replaced subscription is itself cancelled.
 *
 * @param field The Atomic container
 * @param instance the instance reference
 * @param s the subscription
 * @param <F> the instance type
 *
 * @return true if replaced
 */
public static <F> boolean set(AtomicReferenceFieldUpdater<F, Subscription> field,
		F instance,
		Subscription s) {
	for (; ; ) {
		Subscription a = field.get(instance);
		if (a == CancelledSubscription.INSTANCE) {
			s.cancel();
			return false;
		}
		if (field.compareAndSet(instance, a, s)) {
			if (a != null) {
				a.cancel();
			}
			return true;
		}
	}
}
 

static <T> boolean removeSequence(final T holder,
                                  final AtomicReferenceFieldUpdater<T, Sequence[]> sequenceUpdater,
                                  final Sequence sequence) {
    int numToRemove;
    Sequence[] oldSequences;
    Sequence[] newSequences;

    do {
        oldSequences = sequenceUpdater.get(holder);

        numToRemove = countMatching(oldSequences, sequence);

        if (0 == numToRemove) {
            break;
        }

        final int oldSize = oldSequences.length;
        newSequences = new Sequence[oldSize - numToRemove];

        for (int i = 0, pos = 0; i < oldSize; i++) {
            final Sequence testSequence = oldSequences[i];
            if (sequence != testSequence) {
                newSequences[pos++] = testSequence;
            }
        }
    } while (!sequenceUpdater.compareAndSet(holder, oldSequences, newSequences));

    return numToRemove != 0;
}
 

/**
 * Object arguments for parameters of type T that are not
 * instances of the class passed to the newUpdater call will
 * result in a ClassCastException being thrown.
 */
public void testFieldUpdaters_ClassCastException() {
    // Use raw types to allow passing wrong object type, provoking CCE
    final AtomicLongFieldUpdater longUpdater = aLongFieldUpdater();
    final AtomicIntegerFieldUpdater intUpdater = anIntFieldUpdater();
    final AtomicReferenceFieldUpdater refUpdater = anIntegerFieldUpdater();
    final Object obj = new Object();
    for (Object x : new Object[]{ new Object(), null }) {
        Runnable[] throwingActions = {
            () -> longUpdater.get(x),
            () -> intUpdater.get(x),
            () -> refUpdater.get(x),

            () -> longUpdater.set(x, 17L),
            () -> intUpdater.set(x, 17),
            () -> refUpdater.set(x, (Integer) 17),

            () -> longUpdater.addAndGet(x, 17L),
            () -> intUpdater.addAndGet(x, 17),

            () -> longUpdater.getAndUpdate(x, y -> y),
            () -> intUpdater.getAndUpdate(x, y -> y),
            () -> refUpdater.getAndUpdate(x, y -> y),

            () -> longUpdater.compareAndSet(x, 17L, 42L),
            () -> intUpdater.compareAndSet(x, 17, 42),
            () -> refUpdater.compareAndSet(x, (Integer) 17, (Integer) 42),
        };
        assertThrows(ClassCastException.class, throwingActions);
    }
}
 

/**
 * 原子移除某个指定的sequence
 *
 * @param holder 原子更新的域所属的类对象
 * @param sequenceUpdater 原子更新的域对象
 * @param sequence 要移除的sequence
 * @param <T>
 * @return
 */
public static <T> boolean removeSequence(
        final T holder,
        final AtomicReferenceFieldUpdater<T, Sequence[]> sequenceUpdater,
        final Sequence sequence)
{
    int numToRemove;
    Sequence[] oldSequences;
    Sequence[] newSequences;

    do
    {
        oldSequences = sequenceUpdater.get(holder);

        numToRemove = countMatching(oldSequences, sequence);

        if (0 == numToRemove)
        {
            break;
        }

        final int oldSize = oldSequences.length;
        newSequences = new Sequence[oldSize - numToRemove];

        for (int i = 0, pos = 0; i < oldSize; i++)
        {
            final Sequence testSequence = oldSequences[i];
            if (sequence != testSequence)
            {
                newSequences[pos++] = testSequence;
            }
        }
    }
    while (!sequenceUpdater.compareAndSet(holder, oldSequences, newSequences));

    return numToRemove != 0;
}
 

/**
 * Atomically replace the {@link Disposable} in the field with the given new Disposable
 * but do not dispose the old one.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @param newValue the new Disposable to set, null allowed
 * @return true if the operation succeeded, false if the target field contained
 * the common {@link #DISPOSED} instance and the given disposable is not null but is disposed.
 */
static <T> boolean replace(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder, @Nullable Disposable newValue) {
	for (;;) {
		Disposable current = updater.get(holder);
		if (current == DISPOSED) {
			if (newValue != null) {
				newValue.dispose();
			}
			return false;
		}
		if (updater.compareAndSet(holder, current, newValue)) {
			return true;
		}
	}
}
 

/**
 * Atomically dispose the {@link Disposable} in the field if not already disposed.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @return true if the {@link Disposable} held by the field was properly disposed
 */
static <T> boolean dispose(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder) {
	Disposable current = updater.get(holder);
	Disposable d = DISPOSED;
	if (current != d) {
		current = updater.getAndSet(holder, d);
		if (current != d) {
			if (current != null) {
				current.dispose();
			}
			return true;
		}
	}
	return false;
}
 

/**
 * Atomically set the field to the given non-null {@link Disposable} and return true,
 * or return false if the field is non-null.
 * If the target field contains the common {@link #DISPOSED} instance, the supplied disposable
 * is disposed. If the field contains other non-null {@link Disposable}, an {@link IllegalStateException}
 * is signalled to the {@code errorCallback}.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @param newValue the new Disposable to set, not null
 * @return true if the operation succeeded, false
 */
public static <T> boolean setOnce(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder, Disposable newValue,
		Consumer<RuntimeException> errorCallback) {
	Objects.requireNonNull(newValue, "newValue is null");
	if (!updater.compareAndSet(holder, null, newValue)) {
		newValue.dispose();
		if (updater.get(holder) != DISPOSED) {
			errorCallback.accept(new IllegalStateException("Disposable already pushed"));
		}
		return false;
	}
	return true;
}
 

/**
 * Atomically replace the {@link Disposable} in the field with the given new Disposable
 * but do not dispose the old one.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @param newValue the new Disposable to set, null allowed
 * @return true if the operation succeeded, false if the target field contained
 * the common {@link #DISPOSED} instance and the given disposable is not null but is disposed.
 */
public static <T> boolean replace(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder, @Nullable Disposable newValue) {
	for (;;) {
		Disposable current = updater.get(holder);
		if (current == DISPOSED) {
			if (newValue != null) {
				newValue.dispose();
			}
			return false;
		}
		if (updater.compareAndSet(holder, current, newValue)) {
			return true;
		}
	}
}
 

/**
 * Atomically dispose the {@link Disposable} in the field if not already disposed.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @return true if the {@link Disposable} held by the field was properly disposed
 */
public static <T> boolean dispose(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder) {
	Disposable current = updater.get(holder);
	Disposable d = DISPOSED;
	if (current != d) {
		current = updater.getAndSet(holder, d);
		if (current != d) {
			if (current != null) {
				current.dispose();
			}
			return true;
		}
	}
	return false;
}
 

/**
 * Atomically try to set the given {@link Disposable} on the field if it is null or
 * disposes it if the field contains {@link #DISPOSED}.
 *
 * @param updater the target field updater
 * @param holder the target instance holding the field
 * @param newValue the disposable to set
 * @return true if successful, false otherwise
 */
public static <T> boolean trySet(AtomicReferenceFieldUpdater<T, Disposable> updater, T holder, Disposable newValue) {
	if (!updater.compareAndSet(holder, null, newValue)) {
		if (updater.get(holder) == DISPOSED) {
			newValue.dispose();
		}
		return false;
	}
	return true;
}
 

private void mutateAdditionalResponseHeaders(
        AtomicReferenceFieldUpdater<DefaultServiceRequestContext, HttpHeaders> atomicUpdater,
        Consumer<HttpHeadersBuilder> mutator) {
    for (;;) {
        final HttpHeaders oldValue = atomicUpdater.get(this);
        final HttpHeadersBuilder builder = oldValue.toBuilder();
        mutator.accept(builder);
        final HttpHeaders newValue = builder.build();
        if (atomicUpdater.compareAndSet(this, oldValue, newValue)) {
            return;
        }
    }
}
 

static <T> boolean removeSequence(final T holder,
		final AtomicReferenceFieldUpdater<T, Sequence[]> sequenceUpdater,
		final Sequence sequence) {
	int numToRemove;
	Sequence[] oldSequences;
	Sequence[] newSequences;

	do {
		oldSequences = sequenceUpdater.get(holder);

		numToRemove = countMatching(oldSequences, sequence);

		if (0 == numToRemove) {
			break;
		}

		final int oldSize = oldSequences.length;
		newSequences = new Sequence[oldSize - numToRemove];

		for (int i = 0, pos = 0; i < oldSize; i++) {
			final Sequence testSequence = oldSequences[i];
			if (sequence != testSequence) {
				newSequences[pos++] = testSequence;
			}
		}
	}
	while (!sequenceUpdater.compareAndSet(holder, oldSequences, newSequences));

	return numToRemove != 0;
}
 

/**
 * A generic utility to atomically replace a subscription or cancel the replacement
 * if the current subscription is marked as already cancelled (as in
 * {@link #cancelledSubscription()}).
 *
 * @param field The Atomic container
 * @param instance the instance reference
 * @param s the subscription
 * @param <F> the instance type
 *
 * @return true if replaced
 */
public static <F> boolean replace(AtomicReferenceFieldUpdater<F, Subscription> field,
		F instance,
		Subscription s) {
	for (; ; ) {
		Subscription a = field.get(instance);
		if (a == CancelledSubscription.INSTANCE) {
			s.cancel();
			return false;
		}
		if (field.compareAndSet(instance, a, s)) {
			return true;
		}
	}
}
 

/**
 * Sets the given subscription once and returns true if successful, false
 * if the field has a subscription already or has been cancelled.
 * <p>
 * If the field already has a subscription, it is cancelled and the duplicate
 * subscription is reported (see {@link #reportSubscriptionSet()}).
 *
 * @param <F> the instance type containing the field
 * @param field the field accessor
 * @param instance the parent instance
 * @param s the subscription to set once
 * @return true if successful, false if the target was not empty or has been cancelled
 */
public static <F> boolean setOnce(AtomicReferenceFieldUpdater<F, Subscription> field, F instance, Subscription s) {
	Objects.requireNonNull(s, "subscription");
	Subscription a = field.get(instance);
	if (a == CancelledSubscription.INSTANCE) {
		s.cancel();
		return false;
	}
	if (a != null) {
		s.cancel();
		reportSubscriptionSet();
		return false;
	}

	if (field.compareAndSet(instance, null, s)) {
		return true;
	}

	a = field.get(instance);

	if (a == CancelledSubscription.INSTANCE) {
		s.cancel();
		return false;
	}

	s.cancel();
	reportSubscriptionSet();
	return false;
}
 

/**
 * Atomically terminates the subscription if it is not already a
 * {@link #cancelledSubscription()}, cancelling the subscription and setting the field
 * to the singleton {@link #cancelledSubscription()}.
 *
 * @param <F> the instance type containing the field
 * @param field the field accessor
 * @param instance the parent instance
 * @return true if terminated, false if the subscription was already terminated
 */
public static <F> boolean terminate(AtomicReferenceFieldUpdater<F, Subscription> field,
		F instance) {
	Subscription a = field.get(instance);
	if (a != CancelledSubscription.INSTANCE) {
		a = field.getAndSet(instance, CancelledSubscription.INSTANCE);
		if (a != null && a != CancelledSubscription.INSTANCE) {
			a.cancel();
			return true;
		}
	}
	return false;
}
 

/**
 * Update an empty atomic reference with the given exception, or combine further added
 * exceptions together as suppressed exceptions under a root Throwable with
 * the {@code "Multiple exceptions"} message, if the atomic reference already holds
 * one. This is short-circuited if the reference contains {@link #TERMINATED}.
 * <p>
 * Since composite exceptions and traceback exceptions share the same underlying mechanism
 * of suppressed exceptions, a traceback could be made part of a composite exception.
 * Use {@link #unwrapMultipleExcludingTracebacks(Throwable)} to filter out such elements in
 * a composite if needed.
 *
 * @param <T> the parent instance type
 * @param field the target field updater
 * @param instance the parent instance for the field
 * @param exception the Throwable to add.
 *
 * @return true if added, false if the field contained the {@link #TERMINATED}
 * instance.
 * @see #unwrapMultiple(Throwable)
 */
public static <T> boolean addThrowable(AtomicReferenceFieldUpdater<T, Throwable> field,
		T instance,
		Throwable exception) {
	for (; ; ) {
		Throwable current = field.get(instance);

		if (current == TERMINATED) {
			return false;
		}

		if (current instanceof CompositeException) {
			//this is ok, composite exceptions are never singletons
			current.addSuppressed(exception);
			return true;
		}

		Throwable update;
		if (current == null) {
			update = exception;
		} else {
			update = multiple(current, exception);
		}

		if (field.compareAndSet(instance, current, update)) {
			return true;
		}
	}
}
 

/**
 * Atomic utility to safely mark a volatile throwable reference with a terminal
 * marker.
 *
 * @param field the atomic container
 * @param instance the reference instance
 * @param <T> the instance type
 *
 * @return the previously masked throwable
 */
@Nullable
public static <T> Throwable terminate(AtomicReferenceFieldUpdater<T, Throwable> field,
		T instance) {
	Throwable current = field.get(instance);
	if (current != TERMINATED) {
		current = field.getAndSet(instance, TERMINATED);
	}
	return current;
}