/*
 * This file is part of FastClasspathScanner.
 *
 * Author: Luke Hutchison
 *
 * Hosted at: https://github.com/lukehutch/fast-classpath-scanner
 *
 * --
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2018 Luke Hutchison
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
 * documentation files (the "Software"), to deal in the Software without restriction, including without
 * limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
 * the Software, and to permit persons to whom the Software is furnished to do so, subject to the following
 * conditions:
 *
 * The above copyright notice and this permission notice shall be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT
 * LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO
 * EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE
 * OR OTHER DEALINGS IN THE SOFTWARE.
 */
package io.github.lukehutch.fastclasspathscanner.utils;

import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * Recycle instances of type T. The method T#close() is called when this class' own close() method is called. Use
 * RuntimeException for type E if the newInstance() method does not throw an exception.
 * 
 * Example usage:
 * 
 * <code>
 *       Recycler<ZipFile, IOException> recycler = new Recycler<>() {
 *           @Override
 *           public ZipFile newInstance() throws IOException {
 *               return new ZipFile(zipFilePath);
 *           }
 *       };
 *       try {
 *           // Repeat the following as many times as needed, on as many threads as needed 
 *           ZipFile zipFile = recycler.acquire();
 *           try {
 *               // Read from zipFile -- don't put recycler.acquire() in the try block, otherwise the finally
 *               // block will try to release the zipfile even if recycler.acquire() failed
 *               // [...]
 *           } finally {
 *               recycler.release(zipFile);
 *               zipFile = null;
 *           }
 *       } catch (IOException e) {
 *           // [...]
 *       } finally {
 *           recycler.close();
 *       }
 * </code>
 */
public abstract class Recycler<T extends AutoCloseable, E extends Exception> implements AutoCloseable {
    /** Instances that have been allocated. */
    private final ConcurrentLinkedQueue<T> allocatedInstances = new ConcurrentLinkedQueue<>();

    /** Instances that have been allocated but are unused. */
    private final ConcurrentLinkedQueue<T> unusedInstances = new ConcurrentLinkedQueue<>();

    /** Acquire or allocate an instance. */
    public T acquire() throws E {
        final T instance = unusedInstances.poll();
        if (instance != null) {
            return instance;
        }
        final T newInstance = newInstance(); // May throw exception E
        if (newInstance != null) {
            allocatedInstances.add(newInstance);
            return newInstance;
        } else {
            throw new RuntimeException("Failed to allocate a new recyclable instance");
        }
    }

    /** Release/recycle an instance. */
    public void release(final T instance) {
        if (instance != null) {
            unusedInstances.add(instance);
        }
    }

    /** Call this only after all instances have been released. */
    @Override
    public void close() {
        final int unreleasedInstances = allocatedInstances.size() - unusedInstances.size();
        if (unreleasedInstances != 0) {
            throw new RuntimeException("Unreleased instances: " + unreleasedInstances);
        }
        for (T instance; (instance = allocatedInstances.poll()) != null;) {
            try {
                instance.close();
            } catch (final Exception e) {
                // Ignore
            }
        }
        unusedInstances.clear();
    }

    /** Create a new instance. */
    public abstract T newInstance() throws E;
}

@@ -1647,16 +1647,93 @@
 *       
+// Autoclose the Recycler when last instance has been released%0A *       try (
 Recycler
@@ -1783,24 +1783,28 @@
 ler%3C%3E() %7B%0A *
+    
            @
@@ -1821,24 +1821,28 @@
 *           
+    
 public ZipFi
@@ -1888,32 +1888,36 @@
 *               
+    
 return new ZipFi
@@ -1950,34 +1950,29 @@
     
+    
 %7D%0A *   
-    %7D;%0A *
        
-try
+ %7D)
  %7B%0A 
@@ -2064,16 +2064,39 @@
 eded %0A *
+           try %7B%0A *    
         
@@ -2145,32 +2145,36 @@
 *           
+  
+  
 try %7B%0A *
             
@@ -2153,32 +2153,36 @@
         try %7B%0A *
+    
                /
@@ -2238,17 +2238,18 @@
 () in th
-e
+is
  try blo
@@ -2265,24 +2265,16 @@
 wise the
- finally
 %0A *     
@@ -2283,18 +2283,30 @@
         
-//
+    // finally
  block w
@@ -2341,18 +2341,20 @@
 le even 
-if
+when
  recycle
@@ -2381,32 +2381,36 @@
 *               
+    
 // %5B...%5D%0A *     
@@ -2411,24 +2411,28 @@
 *           
+ 
+   
 %7D finally %7B%0A
@@ -2425,32 +2425,36 @@
   %7D finally %7B%0A *
+    
                r
@@ -2496,16 +2496,20 @@
         
+ 
+   
 zipFile 
@@ -2525,28 +2525,36 @@
 *           
-%7D%0A *
+    %7D%0A *    
        %7D cat
@@ -2591,68 +2591,65 @@
     
-// %5B...%5D%0A *       %7D finally %7B%0A *           recycler.close();
+    // May be thrown by recycler.acquire()%0A *           %7D
 %0A * 

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