Adding Javadocs for the Locks.Lock class. Improvements in the test suite.
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Jochen Wiedmann
Rob Tompkins
parent
acaf458278
commit
bf7aa89ca4
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@ -70,31 +70,174 @@ import org.apache.commons.lang3.function.FailableFunction;
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*/
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public class Locks {
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/**
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* This class implements a wrapper for a locked (hidden) object, and
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* provides the means to access it. The basic idea, is that the user
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* code forsakes all references to the locked object, using only the
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* wrapper object, and the accessor methods
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* {@link #acceptReadLocked(FailableConsumer)},
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* {@link #acceptWriteLocked(FailableConsumer)},
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* {@link #applyReadLocked(FailableFunction)}, and
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* {@link #applyWriteLocked(FailableFunction)}. By doing so, the
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* necessary protections are guaranteed.
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* @param <O> The locked (hidden) objects type.
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*
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* @since 3.11
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*/
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public static class Lock<O extends Object> {
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private final StampedLock lock = new StampedLock();
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private final O lockedObject;
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/**
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* Creates a new instance with the given locked object. This
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* constructor is supposed to be used for subclassing only.
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* In general, it is suggested to use {@link Locks#lock(Object)}
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* instead.
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* @param lockedObject The locked (hidden) object. The caller is
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* supposed to drop all references to the locked object.
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*/
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public Lock(final O lockedObject) {
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this.lockedObject = Objects.requireNonNull(lockedObject, "Locked Object");
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}
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/**
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* Provides read (shared, non-exclusive) access to the locked (hidden) object.
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* More precisely, what the method will do (in the given order):
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* <ol>
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* <li>Obtain a read (shared) lock on the locked (hidden) object.
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* The current thread may block, until such a lock is granted.
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* </li>
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* <li>Invokes the given {@link FailableConsumer consumer}, passing the
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* locked object as the parameter.</li>
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* <li>Release the lock, as soon as the consumers invocation is done.
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* If the invocation results in an error, the lock will be released
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* anyways.
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* </li>
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* </ol>
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* @param consumer The consumer, which is being invoked to use the
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* hidden object, which will be passed as the consumers parameter.
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* @see #acceptWriteLocked(FailableConsumer)
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* @see #applyReadLocked(FailableFunction)
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*/
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public void acceptReadLocked(final FailableConsumer<O, ?> consumer) {
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lockAcceptUnlock(() -> lock.readLock(), consumer);
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}
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/**
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* Provides write (exclusive) access to the locked (hidden) object.
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* More precisely, what the method will do (in the given order):
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* <ol>
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* <li>Obtain a write (shared) lock on the locked (hidden) object.
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* The current thread may block, until such a lock is granted.
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* </li>
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* <li>Invokes the given {@link FailableConsumer consumer}, passing the
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* locked object as the parameter.</li>
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* <li>Release the lock, as soon as the consumers invocation is done.
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* If the invocation results in an error, the lock will be released
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* anyways.
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* </li>
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* </ol>
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* @param consumer The consumer, which is being invoked to use the
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* hidden object, which will be passed as the consumers parameter.
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* @see #acceptReadLocked(FailableConsumer)
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* @see #applyWriteLocked(FailableFunction)
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*/
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public void acceptWriteLocked(final FailableConsumer<O, ?> consumer) {
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lockAcceptUnlock(() -> lock.writeLock(), consumer);
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}
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/**
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* Provides read (shared, non-exclusive) access to the locked (hidden)
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* object for the purpose of computing a result object.
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* More precisely, what the method will do (in the given order):
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* <ol>
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* <li>Obtain a read (shared) lock on the locked (hidden) object.
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* The current thread may block, until such a lock is granted.
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* </li>
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* <li>Invokes the given {@link FailableFunction function}, passing the
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* locked object as the parameter, receiving the functions result.</li>
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* <li>Release the lock, as soon as the consumers invocation is done.
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* If the invocation results in an error, the lock will be released
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* anyways.
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* </li>
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* <li>
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* Return the result object, that has been received from the
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* functions invocation.</li>
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* </ol>
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*
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* <em>Example:</em> Suggest, that the hidden object is a list, and we
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* wish to know the current size of the list. This might be achieved
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* with the following:
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*
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* <pre>
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* private Lock<List<Object>> listLock;
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*
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* public int getCurrentListSize() {
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* final Integer sizeInteger
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* = listLock.applyReadLocked((list) -> Integer.valueOf(list.size));
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* return sizeInteger.intValue();
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* }
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* </pre>
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* @param <T> The result type (both the functions, and this method's.)
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* @param function The function, which is being invoked to compute the
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* result. The function will receive the hidden object.
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* @return The result object, which has been returned by the
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* functions invocation.
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* @throws IllegalStateException The result object would be, in fact,
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* the hidden object. This would extend access to the hidden object
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* beyond this methods lifetime and will therefore be prevented.
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* @see #acceptReadLocked(FailableConsumer)
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* @see #applyWriteLocked(FailableFunction)
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*/
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public <T> T applyReadLocked(final FailableFunction<O, T, ?> function) {
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return lockApplyUnlock(() -> lock.readLock(), function);
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}
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/**
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* Provides write (exclusive) access to the locked (hidden)
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* object for the purpose of computing a result object.
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* More precisely, what the method will do (in the given order):
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* <ol>
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* <li>Obtain a read (shared) lock on the locked (hidden) object.
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* The current thread may block, until such a lock is granted.
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* </li>
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* <li>Invokes the given {@link FailableFunction function}, passing the
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* locked object as the parameter, receiving the functions result.</li>
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* <li>Release the lock, as soon as the consumers invocation is done.
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* If the invocation results in an error, the lock will be released
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* anyways.
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* </li>
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* <li>
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* Return the result object, that has been received from the
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* functions invocation.</li>
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* </ol>
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* @param <T> The result type (both the functions, and this method's.)
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* @param function The function, which is being invoked to compute the
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* result. The function will receive the hidden object.
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* @return The result object, which has been returned by the
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* functions invocation.
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* @throws IllegalStateException The result object would be, in fact,
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* the hidden object. This would extend access to the hidden object
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* beyond this methods lifetime and will therefore be prevented.
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* @see #acceptReadLocked(FailableConsumer)
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* @see #applyWriteLocked(FailableFunction)
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*/
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public <T> T applyWriteLocked(final FailableFunction<O, T, ?> function) {
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return lockApplyUnlock(() -> lock.writeLock(), function);
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}
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/**
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* This method provides the actual implementation for
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* {@link #acceptReadLocked(FailableConsumer)}, and
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* {@link #acceptWriteLocked(FailableConsumer)}.
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* @param stampSupplier A supplier for the lock. (This provides, in
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* fact, a long, because a {@link StampedLock} is used internally.)
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* @param consumer The consumer, which is to be given access to the
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* locked (hidden) object, which will be passed as a parameter.
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* @see #acceptReadLocked(FailableConsumer)
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* @see #acceptWriteLocked(FailableConsumer)
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* @see #lockApplyUnlock(LongSupplier, FailableFunction)
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*/
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protected void lockAcceptUnlock(final LongSupplier stampSupplier, final FailableConsumer<O, ?> consumer) {
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final long stamp = stampSupplier.getAsLong();
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try {
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@ -106,10 +249,33 @@ public class Locks {
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}
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}
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/**
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* This method provides the actual implementation for
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* {@link #applyReadLocked(FailableFunction)}, and
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* {@link #applyWriteLocked(FailableFunction)}.
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* @param <T> The result type (both the functions, and this method's.)
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* @param stampSupplier A supplier for the lock. (This provides, in
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* fact, a long, because a {@link StampedLock} is used internally.)
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* @param function The function, which is being invoked to compute
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* the result object. This function will receive the locked (hidden)
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* object as a parameter.
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* @return The result object, which has been returned by the
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* functions invocation.
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* @throws IllegalStateException The result object would be, in fact,
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* the hidden object. This would extend access to the hidden object
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* beyond this methods lifetime and will therefore be prevented.
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* @see #applyReadLocked(FailableFunction)
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* @see #applyWriteLocked(FailableFunction)
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* @see #lockAcceptUnlock(LongSupplier, FailableConsumer)
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*/
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protected <T> T lockApplyUnlock(final LongSupplier stampSupplier, final FailableFunction<O, T, ?> function) {
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final long stamp = stampSupplier.getAsLong();
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try {
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return function.apply(lockedObject);
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final T t = function.apply(lockedObject);
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if (t == lockedObject) {
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throw new IllegalStateException("The returned object is, in fact, the hidden object.");
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}
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return t;
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} catch (final Throwable t) {
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throw Failable.rethrow(t);
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} finally {
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@ -118,6 +284,14 @@ public class Locks {
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}
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}
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/**
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* Creates a new instance of {@link Lock} with the given locked
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* (hidden) object.
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* @param <O> The locked objects type.
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* @param object The locked (hidden) object.
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* @return The created instance, a {@link Lock lock} for the
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* given object.
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*/
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public static <O extends Object> Locks.Lock<O> lock(final O object) {
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return new Locks.Lock<>(object);
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}
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@ -16,7 +16,11 @@
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*/
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package org.apache.commons.lang3.concurrent;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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import static org.junit.jupiter.api.Assertions.assertNotSame;
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import static org.junit.jupiter.api.Assertions.assertTrue;
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import static org.junit.jupiter.api.Assertions.fail;
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import java.util.function.LongConsumer;
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@ -36,6 +40,7 @@ public class LocksTest {
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runTest(DELAY, false, l -> assertTrue(l < NUMBER_OF_THREADS*DELAY));
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}
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@Test
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public void testWriteLock() throws Exception {
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final long DELAY = 100;
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/** If our threads are running concurrently, then we expect to be no faster
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@ -44,6 +49,38 @@ public class LocksTest {
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runTest(DELAY, true, l -> assertTrue(l >= NUMBER_OF_THREADS*DELAY));
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}
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@Test
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public void testResultValidation() {
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final Object hidden = new Object();
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final Lock<Object> lock = Locks.lock(hidden);
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final Object o1 = lock.applyReadLocked((h) -> {
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return new Object();
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});
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assertNotNull(o1);
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assertNotSame(hidden, o1);
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final Object o2 = lock.applyWriteLocked((h) -> {
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return new Object();
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});
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assertNotNull(o2);
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assertNotSame(hidden, o2);
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try {
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lock.applyReadLocked((h) -> {
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return hidden;
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});
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fail("Expected Exception");
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} catch (IllegalStateException e) {
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assertEquals("The returned object is, in fact, the hidden object.", e.getMessage());
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}
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try {
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lock.applyReadLocked((h) -> {
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return hidden;
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});
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fail("Expected Exception");
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} catch (IllegalStateException e) {
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assertEquals("The returned object is, in fact, the hidden object.", e.getMessage());
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}
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}
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private void runTest(final long delay, final boolean exclusiveLock, final LongConsumer runTimeCheck) throws InterruptedException {
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final boolean[] booleanValues = new boolean[10];
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final Lock<boolean[]> lock = Locks.lock(booleanValues);
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