Adding apex plugins/plugins-context modules

Change-Id: I36fc295ffbd22661bf8bd091bfb20ebf6dcc7f5e
Issue-ID: POLICY-862
Signed-off-by: waqas.ikram <waqas.ikram@ericsson.com>

6 files changed, 604 insertions, 0 deletions

diff --git a/plugins/plugins-context/context-locking/context-locking-curator/pom.xml b/plugins/plugins-context/context-locking/context-locking-curator/pom.xml
new file mode 100644
index 000000000..d5d50e1a1
--- /dev/null
+++ b/plugins/plugins-context/context-locking/context-locking-curator/pom.xml
@@ -0,0 +1,45 @@
+<!--
+  ============LICENSE_START=======================================================
+   Copyright (C) 2018 Ericsson. All rights reserved.
+  ================================================================================
+  Licensed under the Apache License, Version 2.0 (the "License");
+  you may not use this file except in compliance with the License.
+  You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing, software
+  distributed under the License is distributed on an "AS IS" BASIS,
+  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+  See the License for the specific language governing permissions and
+  limitations under the License.
+
+  SPDX-License-Identifier: Apache-2.0
+  ============LICENSE_END=========================================================
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>org.onap.policy.apex-pdp.plugins.plugins-context.context-locking</groupId>
+        <artifactId>context-locking</artifactId>
+        <version>2.0.0-SNAPSHOT</version>
+    </parent>
+
+    <artifactId>context-locking-curator</artifactId>
+    <name>${project.artifactId}</name>
+    <description>[${project.parent.artifactId}] Plugin for locking using Curator</description>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.curator</groupId>
+            <artifactId>curator-framework</artifactId>
+            <version>4.0.0</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.curator</groupId>
+            <artifactId>curator-recipes</artifactId>
+            <version>4.0.0</version>
+        </dependency>
+    </dependencies>
+</project>
\ No newline at end of file
diff --git a/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockFacade.java b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockFacade.java
new file mode 100644
index 000000000..928255031
--- /dev/null
+++ b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockFacade.java
@@ -0,0 +1,137 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.apex.plugins.context.locking.curator;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.Lock;
+
+import org.apache.curator.framework.recipes.locks.InterProcessMutex;
+import org.slf4j.ext.XLogger;
+import org.slf4j.ext.XLoggerFactory;
+
+/**
+ * This class provides a facade over the {@link Lock} interface for Curator locks.
+ *
+ * @author Liam Fallon (liam.fallon@ericsson.com)
+ */
+public class CuratorLockFacade implements Lock {
+    // Logger for this class
+    private static final XLogger LOGGER = XLoggerFactory.getXLogger(CuratorLockFacade.class);
+
+    // The Lock ID
+    private final String lockId;
+
+    // The mutex used for Curator locking
+    private final InterProcessMutex lockMutex;
+
+    /**
+     * Create the lock Facade.
+     *
+     * @param lockMutex The lock mutex behind the facade
+     * @param lockId The ID of the lock
+     */
+    public CuratorLockFacade(final InterProcessMutex lockMutex, final String lockId) {
+        this.lockId = lockId;
+        this.lockMutex = lockMutex;
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.Lock#lock()
+     */
+    @Override
+    public void lock() {
+        try {
+            lockMutex.acquire();
+        } catch (final Exception e) {
+            LOGGER.warn("failed to acquire lock for \"" + lockId, e);
+        }
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.Lock#lockInterruptibly()
+     */
+    @Override
+    public void lockInterruptibly() throws InterruptedException {
+        LOGGER.warn("lockInterruptibly() not supported for \"" + lockId);
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.Lock#tryLock()
+     */
+    @Override
+    public boolean tryLock() {
+        try {
+            lockMutex.acquire();
+            return true;
+        } catch (final Exception e) {
+            LOGGER.warn("failed to acquire lock for \"" + lockId, e);
+            return false;
+        }
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.Lock#tryLock(long, java.util.concurrent.TimeUnit)
+     */
+    @Override
+    public boolean tryLock(final long time, final TimeUnit unit) throws InterruptedException {
+        try {
+            lockMutex.acquire(time, unit);
+            return true;
+        } catch (final Exception e) {
+            LOGGER.warn("failed to acquire lock for \"" + lockId, e);
+            return false;
+        }
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.Lock#unlock()
+     */
+    @Override
+    public void unlock() {
+        try {
+            lockMutex.release();
+        } catch (final Exception e) {
+            LOGGER.warn("failed to release lock for \"" + lockId, e);
+        }
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.Lock#newCondition()
+     */
+    @Override
+    public Condition newCondition() {
+        LOGGER.warn("newCondition() not supported for \"" + lockId);
+        return null;
+    }
+}
diff --git a/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockManager.java b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockManager.java
new file mode 100644
index 000000000..d0cc842fd
--- /dev/null
+++ b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockManager.java
@@ -0,0 +1,185 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.apex.plugins.context.locking.curator;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.ReadWriteLock;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.CuratorFrameworkFactory;
+import org.apache.curator.framework.state.ConnectionState;
+import org.apache.curator.framework.state.ConnectionStateListener;
+import org.apache.curator.retry.ExponentialBackoffRetry;
+import org.apache.curator.utils.CloseableUtils;
+import org.apache.zookeeper.CreateMode;
+import org.onap.policy.apex.context.ContextException;
+import org.onap.policy.apex.context.impl.locking.AbstractLockManager;
+import org.onap.policy.apex.model.basicmodel.concepts.AxArtifactKey;
+import org.onap.policy.apex.model.basicmodel.service.ParameterService;
+import org.slf4j.ext.XLogger;
+import org.slf4j.ext.XLoggerFactory;
+
+/**
+ * The Class CuratorLockManager manages the Curator interface towards Zookeeper for administering
+ * the Apex Context Album instance locks..
+ */
+public class CuratorLockManager extends AbstractLockManager {
+    // Logger for this class
+    private static final XLogger LOGGER = XLoggerFactory.getXLogger(CuratorLockManager.class);
+
+    // The Curator framework used for locking
+    private CuratorFramework curatorFramework;
+
+    // The address of the Zookeeper server
+    private String curatorZookeeperAddress;
+
+    /**
+     * Constructor, set up a lock manager that uses Curator locking.
+     *
+     * @throws ContextException On errors connecting to Curator
+     */
+    public CuratorLockManager() throws ContextException {
+        LOGGER.entry("CuratorLockManager(): setting up the Curator lock manager . . .");
+
+        LOGGER.exit("CuratorLockManager(): Curator lock manager set up");
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see org.onap.policy.apex.context.impl.locking.AbstractLockManager#init(org.onap.policy.apex.
+     * model. basicmodel.concepts.AxArtifactKey)
+     */
+    @Override
+    public void init(final AxArtifactKey key) throws ContextException {
+        LOGGER.entry("init(" + key + ")");
+
+        super.init(key);
+
+        // Get the lock manager parameters
+        final CuratorLockManagerParameters lockParameters =
+                ParameterService.getParameters(CuratorLockManagerParameters.class);
+
+        // Check if the curator address has been set
+        curatorZookeeperAddress = lockParameters.getZookeeperAddress();
+        if (curatorZookeeperAddress == null || curatorZookeeperAddress.trim().length() == 0) {
+            LOGGER.warn(
+                    "could not set up Curator locking, check if the curator Zookeeper address parameter is set correctly");
+            throw new ContextException(
+                    "could not set up Curator locking, check if the curator Zookeeper address parameter is set correctly");
+        }
+
+        // Set up the curator framework we'll use
+        curatorFramework = CuratorFrameworkFactory.builder().connectString(curatorZookeeperAddress)
+                .retryPolicy(new ExponentialBackoffRetry(lockParameters.getZookeeperConnectSleepTime(),
+                        lockParameters.getZookeeperContextRetries()))
+                .build();
+
+        // Listen for changes on the Curator connection
+        curatorFramework.getConnectionStateListenable().addListener(new CuratorManagerConnectionStateListener());
+
+        // Start the framework and specify Ephemeral nodes
+        curatorFramework.start();
+
+        // Wait for the connection to be made
+        try {
+            curatorFramework.blockUntilConnected(
+                    lockParameters.getZookeeperConnectSleepTime() * lockParameters.getZookeeperContextRetries(),
+                    TimeUnit.MILLISECONDS);
+        } catch (final InterruptedException e) {
+            LOGGER.warn("could not connect to Zookeeper server at \"" + curatorZookeeperAddress
+                    + "\", wait for connection timed out");
+            throw new ContextException("could not connect to Zookeeper server at \"" + curatorZookeeperAddress
+                    + "\", wait for connection timed out");
+        }
+
+        if (!curatorFramework.getZookeeperClient().isConnected()) {
+            LOGGER.warn("could not connect to Zookeeper server at \"" + curatorZookeeperAddress
+                    + "\", see error log for details");
+            throw new ContextException("could not connect to Zookeeper server at \"" + curatorZookeeperAddress
+                    + "\", see error log for details");
+        }
+
+        // We'll use Ephemeral nodes for locks on the Zookeeper server
+        curatorFramework.create().withMode(CreateMode.EPHEMERAL_SEQUENTIAL);
+
+        LOGGER.exit("init(" + key + "," + lockParameters + ")");
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see
+     * org.onap.policy.apex.core.context.impl.locking.AbstractLockManager#getReentrantReadWriteLock(
+     * java.lang.String)
+     */
+    @Override
+    public ReadWriteLock getReentrantReadWriteLock(final String lockId) throws ContextException {
+        // Check if the framework is active
+        if (curatorFramework != null && curatorFramework.getZookeeperClient().isConnected()) {
+            return new CuratorReentrantReadWriteLock(curatorFramework, "/" + lockId);
+        } else {
+            throw new ContextException("creation of lock using Zookeeper server at \"" + curatorZookeeperAddress
+                    + "\", failed, see error log for details");
+        }
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see org.onap.policy.apex.core.context.LockManager#shutdown()
+     */
+    @Override
+    public void shutdown() {
+        if (curatorFramework == null) {
+            return;
+        }
+        CloseableUtils.closeQuietly(curatorFramework);
+        curatorFramework = null;
+    }
+
+    /**
+     * This class is a callback class for state changes on the curator to Zookeeper connection.
+     */
+    private class CuratorManagerConnectionStateListener implements ConnectionStateListener {
+
+        /*
+         * (non-Javadoc)
+         *
+         * @see org.apache.curator.framework.state.ConnectionStateListener#stateChanged(org.apache.
+         * curator.framework.CuratorFramework, org.apache.curator.framework.state.ConnectionState)
+         */
+        @Override
+        public void stateChanged(final CuratorFramework incomngCuratorFramework, final ConnectionState newState) {
+            // Is the state changed for this curator framework?
+            if (!incomngCuratorFramework.equals(curatorFramework)) {
+                return;
+            }
+
+            LOGGER.info("curator state of client \"" + curatorFramework + "\" connected to \"" + curatorZookeeperAddress
+                    + "\" changed to " + newState);
+
+            if (newState != ConnectionState.CONNECTED) {
+                shutdown();
+            }
+        }
+    }
+}
diff --git a/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockManagerParameters.java b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockManagerParameters.java
new file mode 100644
index 000000000..9e8d5d2af
--- /dev/null
+++ b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorLockManagerParameters.java
@@ -0,0 +1,120 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.apex.plugins.context.locking.curator;
+
+import org.onap.policy.apex.context.parameters.LockManagerParameters;
+import org.onap.policy.apex.model.basicmodel.service.ParameterService;
+
+/**
+ * Bean class for Curator locking parameters.
+ *
+ * @author Liam Fallon (liam.fallon@ericsson.com)
+ */
+public class CuratorLockManagerParameters extends LockManagerParameters {
+    // @formatter:off
+    /** The default address used to connect to the Zookeeper server. */
+    public static final String DEFAULT_ZOOKEEPER_ADDRESS            = "localhost:2181";
+
+    /** The default sleep time to use when connecting to the Zookeeper server. */
+    public static final int DEFAULT_ZOOKEEPER_CONNECT_SLEEP_TIME = 1000;
+
+    /** The default number of times to retry failed connections to the Zookeeper server. */
+    public static final int DEFAULT_ZOOKEEPER_CONNECT_RETRIES = 3;
+
+    // Curator parameters
+    private String zookeeperAddress       = DEFAULT_ZOOKEEPER_ADDRESS;
+    private int zookeeperConnectSleepTime = DEFAULT_ZOOKEEPER_CONNECT_SLEEP_TIME;
+    private int zookeeperContextRetries   = DEFAULT_ZOOKEEPER_CONNECT_RETRIES;
+    // @formatter:on
+
+    /**
+     * The Constructor.
+     */
+    public CuratorLockManagerParameters() {
+        super(CuratorLockManagerParameters.class.getCanonicalName());
+        ParameterService.registerParameters(CuratorLockManagerParameters.class, this);
+    }
+
+    /**
+     * Gets the zookeeper address.
+     *
+     * @return the zookeeper address
+     */
+    public String getZookeeperAddress() {
+        return zookeeperAddress;
+    }
+
+    /**
+     * Sets the zookeeper address.
+     *
+     * @param zookeeperAddress the zookeeper address
+     */
+    public void setZookeeperAddress(final String zookeeperAddress) {
+        this.zookeeperAddress = zookeeperAddress;
+    }
+
+    /**
+     * Gets the zookeeper connect sleep time.
+     *
+     * @return the zookeeper connect sleep time
+     */
+    public int getZookeeperConnectSleepTime() {
+        return zookeeperConnectSleepTime;
+    }
+
+    /**
+     * Sets the zookeeper connect sleep time.
+     *
+     * @param zookeeperConnectSleepTime the zookeeper connect sleep time
+     */
+    public void setZookeeperConnectSleepTime(final int zookeeperConnectSleepTime) {
+        this.zookeeperConnectSleepTime = zookeeperConnectSleepTime;
+    }
+
+    /**
+     * Gets the zookeeper context retries.
+     *
+     * @return the zookeeper context retries
+     */
+    public int getZookeeperContextRetries() {
+        return zookeeperContextRetries;
+    }
+
+    /**
+     * Sets the zookeeper context retries.
+     *
+     * @param zookeeperContextRetries the zookeeper context retries
+     */
+    public void setZookeeperContextRetries(final int zookeeperContextRetries) {
+        this.zookeeperContextRetries = zookeeperContextRetries;
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see org.onap.policy.apex.context.parameters.LockManagerParameters#toString()
+     */
+    @Override
+    public String toString() {
+        return "CuratorLockManagerParameters [zookeeperAddress=" + zookeeperAddress + ", zookeeperConnectSleepTime="
+                + zookeeperConnectSleepTime + ", zookeeperContextRetries=" + zookeeperContextRetries + "]";
+    }
+}
diff --git a/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorReentrantReadWriteLock.java b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorReentrantReadWriteLock.java
new file mode 100644
index 000000000..22bf5e596
--- /dev/null
+++ b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/CuratorReentrantReadWriteLock.java
@@ -0,0 +1,90 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+package org.onap.policy.apex.plugins.context.locking.curator;
+
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReadWriteLock;
+
+import org.apache.curator.framework.CuratorFramework;
+import org.apache.curator.framework.recipes.locks.InterProcessReadWriteLock;
+
+/**
+ * This class maps a Curator {@link InterProcessReadWriteLock} to a Java {@link ReadWriteLock}.
+ *
+ * @author Liam Fallon (liam.fallon@ericsson.com)
+ */
+public class CuratorReentrantReadWriteLock implements ReadWriteLock {
+    // The Lock ID
+    private final String lockID;
+
+    // The Curator lock
+    private final InterProcessReadWriteLock curatorReadWriteLock;
+
+    // The Curator Lock facades for read and write locks
+    private final CuratorLockFacade readLockFacade;
+    private final CuratorLockFacade writeLockFacade;
+
+    /**
+     * Create a Curator lock.
+     *
+     * @param curatorFramework the Curator framework to use to create the lock
+     * @param lockId The unique ID of the lock.
+     */
+    public CuratorReentrantReadWriteLock(final CuratorFramework curatorFramework, final String lockId) {
+        lockID = lockId;
+
+        // Create the Curator lock
+        curatorReadWriteLock = new InterProcessReadWriteLock(curatorFramework, lockId);
+
+        // Create the lock facades
+        readLockFacade = new CuratorLockFacade(curatorReadWriteLock.readLock(), lockId);
+        writeLockFacade = new CuratorLockFacade(curatorReadWriteLock.writeLock(), lockId);
+    }
+
+    /**
+     * Get the lock Id of the lock.
+     *
+     * @return the lock ID
+     */
+    public String getLockID() {
+        return lockID;
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.ReadWriteLock#readLock()
+     */
+    @Override
+    public Lock readLock() {
+        return readLockFacade;
+    }
+
+    /*
+     * (non-Javadoc)
+     *
+     * @see java.util.concurrent.locks.ReadWriteLock#writeLock()
+     */
+    @Override
+    public Lock writeLock() {
+        return writeLockFacade;
+    }
+}
diff --git a/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/package-info.java b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/package-info.java
new file mode 100644
index 000000000..d867c396a
--- /dev/null
+++ b/plugins/plugins-context/context-locking/context-locking-curator/src/main/java/org/onap/policy/apex/plugins/context/locking/curator/package-info.java
@@ -0,0 +1,27 @@
+/*-
+ * ============LICENSE_START=======================================================
+ *  Copyright (C) 2016-2018 Ericsson. All rights reserved.
+ * ================================================================================
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * 
+ * SPDX-License-Identifier: Apache-2.0
+ * ============LICENSE_END=========================================================
+ */
+
+/**
+ * Implements locking on context items in APEX context albums using
+ * <a href="http://curator.apache.org/">Curator</a> centralized locking.
+ *
+ * @author Liam Fallon (liam.fallon@ericsson.com)
+ */
+package org.onap.policy.apex.plugins.context.locking.curator;