HTTPCLIENT-1749: OSGi client builder to use weak references to track HttpClient instances

Contributed by Justin Edelson <justin at justinedelson.com>

git-svn-id: https://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk@1747905 13f79535-47bb-0310-9956-ffa450edef68

httpclient5-osgi/pom.xml

@@ -215,13 +215,6 @@
             <_removeheaders>JAVA_1_3_HOME,JAVA_1_4_HOME</_removeheaders>
           </instructions>
         </configuration>
-      </plugin>
-      <plugin>
-        <groupId>org.codehaus.mojo</groupId>
-        <artifactId>clirr-maven-plugin</artifactId>
-        <configuration>
-          <skip>true</skip>
-        </configuration>
       </plugin>
         <plugin>
             <groupId>org.apache.maven.plugins</groupId>

httpclient5-osgi/src/main/java/org/apache/hc/client5/http/osgi/impl/HttpProxyConfigurationActivator.java

@@ -31,7 +31,6 @@ import java.io.IOException;
 import java.util.Dictionary;
 import java.util.Hashtable;
 import java.util.LinkedHashMap;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Map;
 
@@ -62,7 +61,11 @@ public final class HttpProxyConfigurationActivator implements BundleActivator, M
 
     private final Map<String, ServiceRegistration> registeredConfigurations = new LinkedHashMap<>();
 
-    private final List<CloseableHttpClient> trackedHttpClients = new LinkedList<>();
+    private final List<CloseableHttpClient> trackedHttpClients;
+
+    public HttpProxyConfigurationActivator() {
+        trackedHttpClients = new WeakList<CloseableHttpClient>();
+    }
 
     /**
      * {@inheritDoc}

httpclient5-osgi/src/main/java/org/apache/hc/client5/http/osgi/impl/OSGiHttpClientBuilder.java

@@ -26,6 +26,7 @@
  */
 package org.apache.hc.client5.http.osgi.impl;
 
+import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 
@@ -39,7 +40,7 @@ import org.osgi.framework.ServiceRegistration;
  */
 final class OSGiHttpClientBuilder extends HttpClientBuilder {
 
-    private final List<CloseableHttpClient> trackedHttpClients;
+    private final Collection<CloseableHttpClient> trackedHttpClients;
 
     public OSGiHttpClientBuilder(
             final BundleContext bundleContext,
@@ -55,7 +56,9 @@ final class OSGiHttpClientBuilder extends HttpClientBuilder {
     @Override
     public CloseableHttpClient build() {
         final CloseableHttpClient httpClient = super.build();
-        trackedHttpClients.add(httpClient);
+        synchronized (trackedHttpClients) {
+            trackedHttpClients.add(httpClient);
+        }
         return httpClient;
     }
 

httpclient5-osgi/src/main/java/org/apache/hc/client5/http/osgi/impl/WeakList.java

@@ -0,0 +1,122 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.client5.http.osgi.impl;
+
+import java.lang.ref.WeakReference;
+import java.util.AbstractList;
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+import java.util.NoSuchElementException;
+
+/**
+ * Implementation of a list backed by WeakReference objects.
+ * This is not a general purpose list and is only meant to be used by this package. It cannot correctly manage null entries by design.
+ */
+class WeakList<T> extends AbstractList<T> {
+
+    private final List<WeakReference<T>> innerList;
+
+    public WeakList() {
+        this.innerList = new ArrayList<WeakReference<T>>();
+    }
+
+    @Override
+    public T get(final int index) {
+        return innerList.get(index).get();
+    }
+
+    @Override
+    public int size() {
+        checkReferences();
+        return innerList.size();
+    }
+
+    @Override
+    public boolean add(final T t) {
+        return innerList.add(new WeakReference<T>(t));
+    }
+
+    private void checkReferences() {
+        final ListIterator<WeakReference<T>> references = innerList.listIterator();
+        while (references.hasNext()) {
+            final WeakReference<T> reference = references.next();
+            if (reference.get() == null) {
+                references.remove();
+            }
+        }
+    }
+
+    @Override
+    public Iterator<T> iterator() {
+        return new WeakIterator<T>(innerList.iterator());
+    }
+
+    private class WeakIterator<T> implements Iterator<T> {
+
+        private final Iterator<WeakReference<T>> innerIterator;
+
+        private WeakReference<T> next;
+
+        public WeakIterator(final Iterator<WeakReference<T>> innerIterator) {
+            this.innerIterator = innerIterator;
+            fetchNext();
+        }
+
+        public boolean hasNext() {
+            return next != null;
+        }
+
+        public T next() {
+            if (next != null) {
+                final T result = next.get();
+                fetchNext();
+                return result;
+            } else {
+                throw new NoSuchElementException();
+            }
+        }
+
+        private void fetchNext() {
+            while (innerIterator.hasNext()) {
+                final WeakReference<T> ref = innerIterator.next();
+                final T obj = ref.get();
+                if (obj != null) {
+                    next = ref;
+                    return;
+                }
+            }
+            next = null;
+        }
+
+        public void remove() {
+            throw new UnsupportedOperationException();
+        }
+
+    }
+}

httpclient5-osgi/src/test/java/org/apache/hc/client5/http/osgi/impl/WeakListTest.java

@@ -0,0 +1,62 @@
+/*
+ * ====================================================================
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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.
+ * ====================================================================
+ *
+ * This software consists of voluntary contributions made by many
+ * individuals on behalf of the Apache Software Foundation.  For more
+ * information on the Apache Software Foundation, please see
+ * <http://www.apache.org/>.
+ *
+ */
+package org.apache.hc.client5.http.osgi.impl;
+
+import org.junit.Test;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertEquals;
+
+public class WeakListTest {
+
+    @Test
+    public void testWeakList() {
+        final WeakList<Object> list = new WeakList<Object>();
+        list.add("hello");
+        list.add(null);
+
+        // null objects are seen as GC'd, so we only expect a size of 1
+        assertEquals(1, list.size());
+
+        final Iterator<Object> it = list.iterator();
+        assertTrue(it.hasNext());
+        assertEquals("hello", it.next());
+        assertFalse(it.hasNext());
+        boolean thrown = false;
+        try {
+            it.next();
+        } catch (NoSuchElementException e) {
+            thrown = true;
+        }
+        assertTrue(thrown);
+    }
+
+}