[GitHub] [wicket] theigl commented on a change in pull request #411: WICKET-6751 Page synchronizer strategies

[GitBox <gi...@apache.org>]

theigl commented on a change in pull request #411: WICKET-6751 Page synchronizer strategies
URL: https://github.com/apache/wicket/pull/411#discussion_r388195392
 
 

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 File path: wicket-core/src/main/java/org/apache/wicket/page/DefaultPageLockManager.java
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 @@ -0,0 +1,201 @@
+package org.apache.wicket.page;
+
+import java.io.Serializable;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.Iterator;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.function.Supplier;
+
+import org.apache.wicket.Application;
+import org.apache.wicket.settings.ExceptionSettings;
+import org.apache.wicket.util.LazyInitializer;
+import org.apache.wicket.util.lang.Threads;
+import org.apache.wicket.util.time.Durations;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Default {@link IPageLockManager} that that holds a map of locks in the current session.
+ * 
+ * @author Igor Vaynberg (ivaynberg)
+ */
+public class DefaultPageLockManager implements IPageLockManager, Serializable {
+
+	private static final long serialVersionUID = 1L;
+
+	private static final Logger logger = LoggerFactory.getLogger(DefaultPageLockManager.class);
+
+	/** map of which pages are owned by which threads */
+	private final Supplier<ConcurrentMap<Integer, PageAccessSynchronizer.PageLock>> locks = new LazyInitializer<ConcurrentMap<Integer, PageAccessSynchronizer.PageLock>>()
+	{
+		private static final long serialVersionUID = 1L;
+
+		@Override
+		protected ConcurrentMap<Integer, PageAccessSynchronizer.PageLock> createInstance()
+		{
+			return new ConcurrentHashMap<>();
+		}
+	};
+
+	/** timeout value for acquiring a page lock */
+	private final Duration timeout;
+
+	/**
+	 * Constructor
+	 *
+	 * @param timeout
+	 *            timeout value for acquiring a page lock
+	 */
+	public DefaultPageLockManager(Duration timeout)
+	{
+		this.timeout = timeout;
+	}
+
+	private static long remaining(Instant start, Duration timeout)
+	{
+		Duration elapsedTime = Durations.elapsedSince(start);
+		return Math.max(0, timeout.minus(elapsedTime).toMillis());
+	}
+
+	/**
+	 * @param pageId
+	 *            the id of the page to be locked
+	 * @return the duration for acquiring a page lock
+	 */
+	public Duration getTimeout(int pageId)
+	{
+		return timeout;
+	}
+
+	@Override
+	public void lockPage(int pageId) throws CouldNotLockPageException
+	{
+		final Thread thread = Thread.currentThread();
+		final PageAccessSynchronizer.PageLock lock = new PageAccessSynchronizer.PageLock(pageId, thread);
+		final Instant start = Instant.now();
+
+		boolean locked = false;
+
+		final boolean isDebugEnabled = logger.isDebugEnabled();
+
+		PageAccessSynchronizer.PageLock previous = null;
+
+		Duration timeout = getTimeout(pageId);
+
+		while (!locked && Durations.elapsedSince(start).compareTo(timeout) < 0)
+		{
+			if (isDebugEnabled)
+			{
+				logger.debug("'{}' attempting to acquire lock to page with id '{}'",
+						thread.getName(), pageId);
+			}
+
+			previous = locks.get().putIfAbsent(pageId, lock);
+
+			if (previous == null || previous.getThread() == thread)
+			{
+				// first thread to acquire lock or lock is already owned by this thread
+				locked = true;
+			}
+			else
+			{
+				// wait for a lock to become available
+				long remaining = remaining(start, timeout);
+				if (remaining > 0)
+				{
+					previous.waitForRelease(remaining, isDebugEnabled);
+				}
+			}
+		}
+		if (locked)
 
 Review comment:
   Done

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