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package com.github.dmgcodevil.jmspy.ext.freemarker;

import com.google.common.annotations.Beta;

import java.util.ArrayDeque;
import java.util.Queue;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Holder based on ThreadLocal to hold information about http servlet request.
 * Ultimately after each invocation of {@link HttpServletRequestInfoHolder#hold(HttpServletRequestInfo)}
 * method must be invoked method {@link com.github.dmgcodevil.jmspy.ext.freemarker.HttpServletRequestInfoHolder#unhold()}
 * otherwise overflow in holder can cause OOM exception.
 *
 * @author dmgcodevil
 */
@Beta
public class HttpServletRequestInfoHolder {

    private static final HttpServletRequestInfoHolder INSTANCE = new HttpServletRequestInfoHolder();

    private static final ThreadLocal> INFO_THREAD_LOCAL =
            new InheritableThreadLocal>() {
                @Override
                protected Queue initialValue() {
                    return new ArrayDeque<>();
                }
            };

    public static HttpServletRequestInfoHolder getInstance() {
        return INSTANCE;
    }

    private final Lock lock = new ReentrantLock();

    public void hold(HttpServletRequestInfo requestInfo) {
        try {
            lock.lock();
            INFO_THREAD_LOCAL.get().add(requestInfo);
        } finally {
            lock.unlock();
        }
    }

    public HttpServletRequestInfo unhold() {
        return INFO_THREAD_LOCAL.get().poll();
    }
}