Add StampedLockFactory and ReadWriteLockFactory

This adds two new factories that generate `StampedLock` and
`ReadWriteLock` instances for applications that require more granular
control over locking. The unit tests duplicate the verifications in
`XMutexFactoryImplTest` and also introduce verifications specific to the
synchronisation mechanisms.

Addresses: #9

src/main/java/com/antkorwin/xsync/ReadWriteLockFactory.java

@@ -0,0 +1,111 @@
+package com.antkorwin.xsync;
+
+import java.util.Objects;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
+import java.util.concurrent.locks.StampedLock;
+import java.util.function.Supplier;
+
+import org.hibernate.validator.internal.util.ConcurrentReferenceHashMap;
+
+/**
+ * Created on 22.06.2020.
+ * <p>
+ * The factory of {@link ReadWriteLock ReadWriteLocks}, based on
+ * {@link ConcurrentReferenceHashMap}. Use this if you need to allow
+ * multiple concurrent readers but only one writer. You can also control
+ * whether or not to support reentrancy and whether or not the lock should
+ * be fair. Depending on your usage patterns, you may opt to back the
+ * locks with a {@link ReentrantReadWriteLock} (default) or a
+ * {@link StampedLock}. Note, for a stamped lock, the optimistic locking
+ * model and lock type modification are not supported.
+ * </p>
+ * 
+ * @author Carlos Macasaet
+ */
+public class ReadWriteLockFactory<KeyT> {
+
+	private static final int DEFAULT_INITIAL_CAPACITY = 16;
+	private static final float DEFAULT_LOAD_FACTOR = 0.75f;
+	private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+	private static final ConcurrentReferenceHashMap.ReferenceType DEFAULT_REFERENCE_TYPE =
+			ConcurrentReferenceHashMap.ReferenceType.WEAK;
+
+	private final ConcurrentMap<KeyT, ReadWriteLock> map;
+	private final Supplier<? extends ReadWriteLock> lockSupplier;
+
+	/**
+	 * Create a lock factory with default settings
+	 */
+	public ReadWriteLockFactory() {
+        this(DEFAULT_CONCURRENCY_LEVEL, DEFAULT_REFERENCE_TYPE);
+	}
+
+	/**
+	 * Create a lock factory with default settings and a custom lock generator.
+	 *
+	 * @param lockSupplier a method for creating new {@link ReadWriteLock} instances.
+	 */
+	public ReadWriteLockFactory(final Supplier<? extends ReadWriteLock> lockSupplier) {
+        this(DEFAULT_CONCURRENCY_LEVEL, DEFAULT_REFERENCE_TYPE, lockSupplier);
+	}
+
+	/**
+	 * Create a lock factory with custom settings
+	 *
+	 * @param concurrencyLevel the expected number of threads
+	 *                         that will concurrently write to the map
+	 * @param referenceType    the reference type used for entries (soft or weak)
+	 */
+    public ReadWriteLockFactory(int concurrencyLevel, ConcurrentReferenceHashMap.ReferenceType referenceType) {
+        this(concurrencyLevel, referenceType, ReentrantReadWriteLock::new);
+    }
+
+	/**
+	 * Create a lock factory with custom settings
+	 * 
+	 * @param concurrencyLevel the expected number of threads
+     *                         that will concurrently write to the map
+	 * @param referenceType    the reference type used for entries (soft or weak)
+	 * @param lockSupplier     a method for creating ReadWriteLock instances
+	 */
+    public ReadWriteLockFactory(final int concurrencyLevel, final ConcurrentReferenceHashMap.ReferenceType referenceType,
+            final Supplier<? extends ReadWriteLock> lockSupplier) {
+	    this(new ConcurrentReferenceHashMap<>(DEFAULT_INITIAL_CAPACITY,
+                DEFAULT_LOAD_FACTOR,
+                concurrencyLevel,
+                referenceType,
+                referenceType,
+                null),
+	            lockSupplier);
+	}
+
+    protected ReadWriteLockFactory(final ConcurrentMap<KeyT, ReadWriteLock> map,
+            final Supplier<? extends ReadWriteLock> lockSupplier) {
+        Objects.requireNonNull(map, "map must be provided");
+        Objects.requireNonNull(lockSupplier, "lockSupplier must be provided");
+        this.map = map;
+        this.lockSupplier = lockSupplier;
+    }
+
+	/**
+	 * Creates and returns a lock by the key.
+	 * If the lock for this key already exists in the weak-map,
+	 * then returns the same reference of the lock.
+	 * 
+	 * @param key object which used as a key for synchronization
+     * @return lock instance created for this key
+	 */
+	public ReadWriteLock getReadWriteLock(KeyT key) {
+		return this.map.computeIfAbsent(key, k -> lockSupplier.get());
+	}
+
+	/**
+	 * @return count of locks in this factory.
+	 */
+	public long size() {
+		return this.map.size();
+	}
+
+}

src/main/java/com/antkorwin/xsync/StampedLockFactory.java

@@ -0,0 +1,85 @@
+package com.antkorwin.xsync;
+
+
+import java.util.Objects;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.locks.StampedLock;
+
+import org.hibernate.validator.internal.util.ConcurrentReferenceHashMap;
+
+
+/**
+ * Created on 22.06.2020.
+ * <p>
+ * The factory of locks, based on {@link ConcurrentReferenceHashMap}.
+ * Use this if you require the performance characteristics of
+ * {@link StampedLock StampedLocks} over other synchronization
+ * mechanisms.
+ * </p>
+ * 
+ * @author Carlos Macasaet
+ */
+public class StampedLockFactory<KeyT> {
+
+	private static final int DEFAULT_INITIAL_CAPACITY = 16;
+	private static final float DEFAULT_LOAD_FACTOR = 0.75f;
+	private static final int DEFAULT_CONCURRENCY_LEVEL = 16;
+	private static final ConcurrentReferenceHashMap.ReferenceType DEFAULT_REFERENCE_TYPE =
+			ConcurrentReferenceHashMap.ReferenceType.WEAK;
+
+	private final ConcurrentMap<KeyT, StampedLock> map;
+
+	/**
+	 * Create a factory with default settings
+	 */
+	public StampedLockFactory() {
+		this(new ConcurrentReferenceHashMap<>(DEFAULT_INITIAL_CAPACITY,
+		                                            DEFAULT_LOAD_FACTOR,
+		                                            DEFAULT_CONCURRENCY_LEVEL,
+		                                            DEFAULT_REFERENCE_TYPE,
+		                                            DEFAULT_REFERENCE_TYPE,
+		                                            null));
+	}
+
+	/**
+	 * Creating a factory with custom settings
+	 *
+	 * @param concurrencyLevel the expected number of threads
+	 *                         that will concurrently write to the map
+	 * @param referenceType    the reference type used for entries (soft or weak)
+	 */
+	public StampedLockFactory(int concurrencyLevel,
+	                         ConcurrentReferenceHashMap.ReferenceType referenceType) {
+		this(new ConcurrentReferenceHashMap<>(DEFAULT_INITIAL_CAPACITY,
+		                                            DEFAULT_LOAD_FACTOR,
+		                                            concurrencyLevel,
+		                                            referenceType,
+		                                            referenceType,
+		                                            null));
+	}
+
+	protected StampedLockFactory(final ConcurrentMap<KeyT, StampedLock> map) {
+	    Objects.requireNonNull(map, "map must be provided");
+	    this.map = map;
+	}
+
+    /**
+     * Creates and returns a lock by the key. If the lock for this key
+     * already exists(or use by another thread), then returns the same
+     * reference of the lock.
+     *
+     * @param key object which used as a key for synchronization
+     * @return lock instance created for this key
+     */
+    public StampedLock getLock(KeyT key) {
+        return this.map.computeIfAbsent(key, k -> new StampedLock());
+    }
+
+	/**
+	 * @return count of locks in this factory.
+	 */
+	public long size() {
+		return this.map.size();
+	}
+
+}