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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/* *******************************************************************
 * Copyright (c) 2004 IBM Corporation
 *
 * All rights reserved.
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Public License v 2.0
 * which accompanies this distribution and is available at
 * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.txt
 *
 * Contributors:
 *    Andy Clement     initial implementation
 * 					   Copied from bits of original CFlowStack
 * ******************************************************************/
package org.aspectj.runtime.internal.cflowstack;

import java.util.Enumeration;
import java.util.Hashtable;
import java.util.Stack;

public class ThreadStackImpl11 implements ThreadStack {
	private Hashtable stacks = new Hashtable<>();
	private Thread cached_thread;
	private Stack cached_stack;
	private int change_count = 0;
	private static final int COLLECT_AT = 20000;
	private static final int MIN_COLLECT_AT = 100;

	public synchronized Stack getThreadStack() {
		if (Thread.currentThread() != cached_thread) {
			cached_thread = Thread.currentThread();
			cached_stack = (Stack)stacks.get(cached_thread);
			if (cached_stack == null) {
				cached_stack = new Stack<>();
				stacks.put(cached_thread, cached_stack);
			}
			change_count++;
			// Collect more often if there are many threads, but not *too* often
			int size = Math.max(1, stacks.size()); // should be >1 b/c always live threads, but...
			if (change_count > Math.max(MIN_COLLECT_AT, COLLECT_AT/size)) {
				Stack dead_stacks = new Stack<>();
				for (Enumeration e = stacks.keys(); e.hasMoreElements(); ) {
					Thread t = e.nextElement();
					if (!t.isAlive()) dead_stacks.push(t);
				}
				for (Enumeration e = dead_stacks.elements(); e.hasMoreElements(); ) {
					Thread t = e.nextElement();
					stacks.remove(t);
				}
				change_count = 0;
			}
		}
		return cached_stack;
	}

	public void removeThreadStack() {
		// TODO
	}

}