/**
 * Copyright 2013 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *    http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.bitcoin.utils;

import com.google.common.util.concurrent.Callables;
import com.google.common.util.concurrent.CycleDetectingLockFactory;
import com.google.common.util.concurrent.Futures;

import javax.annotation.Nonnull;
import java.util.concurrent.*;
import java.util.concurrent.locks.ReentrantLock;

import static com.google.common.base.Preconditions.checkState;

/**
 * Various threading related utilities. Provides a wrapper around explicit lock creation that lets you control whether
 * bitcoinj performs cycle detection or not. Cycle detection is useful to detect bugs but comes with a small cost.
 * Also provides a worker thread that is designed for event listeners to be dispatched on.
 */
public class Threading {
    /**
     * An executor with one thread that is intended for running event listeners on. This ensures all event listener code
     * runs without any locks being held. It's intended for the API user to run things on. Callbacks registered by
     * bitcoinj internally shouldn't normally run here, although currently there are a few exceptions.
     */
    public static final ExecutorService USER_THREAD;

    /**
     * A dummy executor that just invokes the runnable immediately. Use this over
     * {@link com.google.common.util.concurrent.MoreExecutors#sameThreadExecutor()} because the latter creates a new
     * object each time in order to implement the more complex {@link ExecutorService} interface, which is overkill
     * for our needs.
     */
    public static final Executor SAME_THREAD;

    // For safety reasons keep track of the thread we use to run user-provided event listeners to avoid deadlock.
    private static Thread userThread;

    /**
     * Put a dummy task into the queue and wait for it to be run. Because it's single threaded, this means all
     * tasks submitted before this point are now completed. Usually you won't want to use this method - it's a
     * convenience primarily used in unit testing. If you want to wait for an event to be called the right thing
     * to do is usually to create a {@link com.google.common.util.concurrent.SettableFuture} and then call set
     * on it. You can then either block on that future, compose it, add listeners to it and so on.
     */
    public static void waitForUserCode() {
        // If this assert fires it means you have a bug in your code - you can't call this method inside your own
        // event handlers because it would never return. If you aren't calling this method explicitly, then that
        // means there's a bug in bitcoinj.
        checkState(userThread != Thread.currentThread(), "waitForUserCode() run on user code thread would deadlock.");
        Futures.getUnchecked(USER_THREAD.submit(Callables.returning(null)));
    }

    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////

    static {
        // Default policy goes here. If you want to change this, use one of the static methods before
        // instantiating any bitcoinj objects. The policy change will take effect only on new objects
        // from that point onwards.
        throwOnLockCycles();

        USER_THREAD = Executors.newSingleThreadExecutor(new ThreadFactory() {
            @Nonnull @Override public Thread newThread(@Nonnull Runnable runnable) {
                checkState(userThread == null, "Not single threaded anymore?");
                userThread = new Thread(runnable);
                userThread.setName("bitcoinj user thread");
                userThread.setDaemon(true);
                return userThread;
            }
        });
        SAME_THREAD = new Executor() {
            @Override
            public void execute(@Nonnull Runnable runnable) {
                runnable.run();
            }
        };
    }

    private static CycleDetectingLockFactory.Policy policy;
    public static CycleDetectingLockFactory factory;

    public static ReentrantLock lock(String name) {
        return factory.newReentrantLock(name);
    }

    public static void warnOnLockCycles() {
        setPolicy(CycleDetectingLockFactory.Policies.WARN);
    }

    public static void throwOnLockCycles() {
        setPolicy(CycleDetectingLockFactory.Policies.THROW);
    }

    public static void ignoreLockCycles() {
        setPolicy(CycleDetectingLockFactory.Policies.DISABLED);
    }

    public static void setPolicy(CycleDetectingLockFactory.Policy policy) {
        Threading.policy = policy;
        factory = CycleDetectingLockFactory.newInstance(policy);
    }

    public static CycleDetectingLockFactory.Policy getPolicy() {
        return policy;
    }
}

@@ -828,16 +828,52 @@
 onnull;%0A
+import java.lang.ref.WeakReference;%0A
 import j
@@ -895,16 +895,16 @@
 rent.*;%0A
-
 import j
@@ -2309,22 +2309,37 @@
  static 
+WeakReference%3C
 Thread
+%3E
  userThr
@@ -3248,16 +3248,50 @@
 erThread
+.get() != null && userThread.get()
  != Thre
@@ -3309,16 +3309,32 @@
 hread(),
+%0A               
  %22waitFo
@@ -4057,98 +4057,16 @@
     
-checkState(userThread == null, %22Not single threaded anymore?%22);%0A                user
 Thread
+ t
  = n
@@ -4098,34 +4098,25 @@
             
-userThread
+t
 .setName(%22bi
@@ -4153,26 +4153,17 @@
         
-userThread
+t
 .setDaem
@@ -4188,23 +4188,16 @@
         
-return 
 userThre
@@ -4198,16 +4198,73 @@
 erThread
+ = new WeakReference%3CThread%3E(t);%0A                return t
 ;%0A      

Fix a bogus assert in Threading