/*
 * Copyright (C) 2009, Google Inc. and others
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0 which is available at
 * https://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.eclipse.jgit.util.io;

import java.text.MessageFormat;

import org.eclipse.jgit.internal.JGitText;

Triggers an interrupt on the calling thread if it doesn't complete a block.

Classes can use this to trip an alarm interrupting the calling thread if it
doesn't complete a block within the specified timeout. Typical calling
pattern is:
private InterruptTimer myTimer = ...;
void foo() {
  try {
    myTimer.begin(timeout);
    // work
  } finally {
    myTimer.end();
  }
}


An InterruptTimer is not recursive. To implement recursive timers,
independent InterruptTimer instances are required. A single InterruptTimer
may be shared between objects which won't recursively call each other.
 Each InterruptTimer spawns one background thread to sleep the specified time and interrupt the thread which called begin(int). It is up to the caller to ensure that the operations within the work block between the matched begin and end calls tests the interrupt flag (most IO operations do). 
 To terminate the background thread, use terminate(). If the application fails to terminate the thread, it will (eventually) terminate itself when the InterruptTimer instance is garbage collected. 
See Also:
TimeoutInputStream/**
 * Triggers an interrupt on the calling thread if it doesn't complete a block.
 * <p>
 * Classes can use this to trip an alarm interrupting the calling thread if it
 * doesn't complete a block within the specified timeout. Typical calling
 * pattern is:
 *
 * <pre>
 * private InterruptTimer myTimer = ...;
 * void foo() {
 *   try {
 *     myTimer.begin(timeout);
 *     // work
 *   } finally {
 *     myTimer.end();
 *   }
 * }
 * </pre>
 * <p>
 * An InterruptTimer is not recursive. To implement recursive timers,
 * independent InterruptTimer instances are required. A single InterruptTimer
 * may be shared between objects which won't recursively call each other.
 * <p>
 * Each InterruptTimer spawns one background thread to sleep the specified time
 * and interrupt the thread which called {@link #begin(int)}. It is up to the
 * caller to ensure that the operations within the work block between the
 * matched begin and end calls tests the interrupt flag (most IO operations do).
 * <p>
 * To terminate the background thread, use {@link #terminate()}. If the
 * application fails to terminate the thread, it will (eventually) terminate
 * itself when the InterruptTimer instance is garbage collected.
 *
 * @see TimeoutInputStream
 */
public final class InterruptTimer {
	private final AlarmState state;

	private final AlarmThread thread;

	final AutoKiller autoKiller;

	
Create a new timer with a default thread name.
/**
	 * Create a new timer with a default thread name.
	 */
	public InterruptTimer() {
		this("JGit-InterruptTimer"); //$NON-NLS-1$
	}

	
Create a new timer to signal on interrupt on the caller.

The timer thread is created in the calling thread's ThreadGroup.
Params:
threadName – 
           name of the timer thread./**
	 * Create a new timer to signal on interrupt on the caller.
	 * <p>
	 * The timer thread is created in the calling thread's ThreadGroup.
	 *
	 * @param threadName
	 *            name of the timer thread.
	 */
	public InterruptTimer(String threadName) {
		state = new AlarmState();
		autoKiller = new AutoKiller(state);
		thread = new AlarmThread(threadName, state);
		thread.start();
	}

	
Arm the interrupt timer before entering a blocking operation.
Params:
timeout – 
           number of milliseconds before the interrupt should trigger.
           Must be > 0./**
	 * Arm the interrupt timer before entering a blocking operation.
	 *
	 * @param timeout
	 *            number of milliseconds before the interrupt should trigger.
	 *            Must be &gt; 0.
	 */
	public void begin(int timeout) {
		if (timeout <= 0)
			throw new IllegalArgumentException(MessageFormat.format(
					JGitText.get().invalidTimeout, Integer.valueOf(timeout)));
		Thread.interrupted();
		state.begin(timeout);
	}

	
Disable the interrupt timer, as the operation is complete.
/**
	 * Disable the interrupt timer, as the operation is complete.
	 */
	public void end() {
		state.end();
	}

	
Shutdown the timer thread, and wait for it to terminate.
/**
	 * Shutdown the timer thread, and wait for it to terminate.
	 */
	public void terminate() {
		state.terminate();
		try {
			thread.join();
		} catch (InterruptedException e) {
			//
		}
	}

	static final class AlarmThread extends Thread {
		AlarmThread(String name, AlarmState q) {
			super(q);
			setName(name);
			setDaemon(true);
		}
	}

	// The trick here is, the AlarmThread does not have a reference to the
	// AutoKiller instance, only the InterruptTimer itself does. Thus when
	// the InterruptTimer is GC'd, the AutoKiller is also unreachable and
	// can be GC'd. When it gets finalized, it tells the AlarmThread to
	// terminate, triggering the thread to exit gracefully.
	//
	private static final class AutoKiller {
		private final AlarmState state;

		AutoKiller(AlarmState s) {
			state = s;
		}

		@Override
		protected void finalize() throws Throwable {
			state.terminate();
		}
	}

	static final class AlarmState implements Runnable {
		private Thread callingThread;

		private long deadline;

		private boolean terminated;

		AlarmState() {
			callingThread = Thread.currentThread();
		}

		@Override
		public synchronized void run() {
			while (!terminated && callingThread.isAlive()) {
				try {
					if (0 < deadline) {
						final long delay = deadline - now();
						if (delay <= 0) {
							deadline = 0;
							callingThread.interrupt();
						} else {
							wait(delay);
						}
					} else {
						wait(1000);
					}
				} catch (InterruptedException e) {
					// Treat an interrupt as notice to examine state.
				}
			}
		}

		synchronized void begin(int timeout) {
			if (terminated)
				throw new IllegalStateException(JGitText.get().timerAlreadyTerminated);
			callingThread = Thread.currentThread();
			deadline = now() + timeout;
			notifyAll();
		}

		synchronized void end() {
			if (0 == deadline)
				Thread.interrupted();
			else
				deadline = 0;
			notifyAll();
		}

		synchronized void terminate() {
			if (!terminated) {
				deadline = 0;
				terminated = true;
				notifyAll();
			}
		}

		private static long now() {
			return System.currentTimeMillis();
		}
	}
}