[GitHub] [ignite] AMashenkov commented on a change in pull request #7569: IGNITE-12804 SQL: ConnectionManager refactoring

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AMashenkov commented on a change in pull request #7569: IGNITE-12804  SQL: ConnectionManager refactoring
URL: https://github.com/apache/ignite/pull/7569#discussion_r402169132
 
 

 ##########
 File path: modules/indexing/src/main/java/org/apache/ignite/internal/processors/query/h2/ConcurrentStripedPool.java
 ##########
 @@ -0,0 +1,177 @@
+/*
+ * 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.
+ */
+
+package org.apache.ignite.internal.processors.query.h2;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.util.concurrent.ConcurrentLinkedQueue;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Consumer;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * Concurrent pool of object based on ConcurrentLinkedDeque.
+ */
+public class ConcurrentStripedPool<E> implements Iterable<E> {
+    /** Stripe pools. */
+    private final ConcurrentLinkedQueue<E>[] stripePools;
+
+    /** Stripes count. */
+    private final int stripes;
+
+    /** Stripe pools size (calculates fast, optimistic and approximate). */
+    private AtomicInteger[] stripeSize;
+
+    /** Max pool size. */
+    private int maxPoolSize;
+
+    /**
+     * Constructor.
+     *
+     * @param stripes Count of stripes.
+     * @param maxPoolSize Max pool size.
+     */
+    @SuppressWarnings("unchecked")
+    public ConcurrentStripedPool(int stripes, int maxPoolSize) {
+        this.stripes = stripes;
+        this.maxPoolSize = maxPoolSize;
+
+        stripePools = new ConcurrentLinkedQueue[stripes];
+        stripeSize = new AtomicInteger[stripes];
+
+        for (int i = 0; i < stripes; ++i) {
+            stripePools[i] = new ConcurrentLinkedQueue<>();
+            stripeSize[i] = new AtomicInteger();
+        }
+    }
+
+    /**
+     * Pushes an element onto the pool.
+     *
+     * @param e the element to push
+     * @throws NullPointerException if the specified element is null and this deque does not permit null elements
+     * @return {@code true} if the element is returned to the pool, {@code false} if the is no space at the pool.
+     */
+    public boolean recycle(E e) {
+        int idx = (int)(Thread.currentThread().getId() % stripes);
+
+        if (stripeSize[idx].get() > maxPoolSize)
+            return false;
+
+        stripePools[idx].add(e);
+
+        stripeSize[idx].incrementAndGet();
+
+        return true;
+    }
+
+    /**
+     * Retrieves element from pool, or returns {@code null} if the pool is empty.
+     *
+     * @return the  element of the pool, or {@code null} if the pool is empty.
+     */
+    public E borrow() {
+        int idx = (int)(Thread.currentThread().getId() % stripes);
+
+        E r = stripePools[idx].poll();
+
+        if (r != null)
+            stripeSize[idx].decrementAndGet();
+
+        return r;
+    }
+
+    /**
+     * Performs the given action for each element of the pool until all elements have been processed or the action
+     * throws an exception. Exceptions thrown by the action are relayed to the caller.
+     *
+     * @param action The action to be performed for each element
+     * @throws NullPointerException if the specified action is null
+     */
+    @Override public void forEach(Consumer<? super E> action) {
+        Objects.requireNonNull(action);
+
+        for (int i = 0; i < stripes; ++i)
+            stripePools[i].forEach(action);
+    }
+
+    /**
+     * Removes all of the elements from the pool..
+     */
+    public void clear() {
+        for (int i = 0; i < stripes; ++i)
+            stripePools[i].clear();
+    }
+
+    /** {@inheritDoc} */
+    @Override public @NotNull Iterator<E> iterator() {
+        return new Iterator<E>() {
+            int idx = 0;
+            Iterator<E> it = stripePools[idx].iterator();
+
+            @Override public boolean hasNext() {
+                if (it.hasNext())
+                    return true;
+
+                idx++;
+
+                if (idx < stripes) {
+                    it = stripePools[idx].iterator();
+
+                    return it.hasNext();
+                }
+                else
+                    return false;
+            }
+
+            @Override public E next() {
+                if (it.hasNext())
+                    return it.next();
+
+                idx++;
+
+                if (idx < stripes) {
+                    it = stripePools[idx].iterator();
+
+                    return it.next();
+                }
+                else
+                    throw new NoSuchElementException();
+            }
+        };
+    }
+
+    /**
+     * Returns a sequential {@code Stream} of the pool.
+     *
+     * @return a sequential {@code Stream} over the elements iof the pool.
+     */
+    public Stream<E> stream() {
+        return StreamSupport.stream(spliterator(), false);
+    }
+
+    /**
+     * @param size New max pool size.
+     */
+    public void resize(int size) {
+        maxPoolSize = size;
+    }
+}
 
 Review comment:
   Empty line.

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