ConditionChecker.java

/*
 *      Copyright (C) 2012-2015 DataStax 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.datastax.driver.core;

import com.google.common.base.Predicate;
import com.google.common.base.Predicates;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.Callable;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

import static org.assertj.core.api.Fail.fail;

public class ConditionChecker {

    private static final int DEFAULT_PERIOD_MILLIS = 500;

    private static final int DEFAULT_TIMEOUT_MILLIS = 60000;

    public static class ConditionCheckerBuilder {

        private long timeout = DEFAULT_TIMEOUT_MILLIS;

        private TimeUnit timeoutUnit = TimeUnit.MILLISECONDS;

        private long period = DEFAULT_PERIOD_MILLIS;

        private TimeUnit periodUnit = TimeUnit.MILLISECONDS;

        private Object input;

        private Predicate<?> predicate;

        public ConditionCheckerBuilder every(long period, TimeUnit unit) {
            this.period = period;
            periodUnit = unit;
            return this;
        }

        public ConditionCheckerBuilder every(long periodMillis) {
            period = periodMillis;
            periodUnit = TimeUnit.MILLISECONDS;
            return this;
        }

        public ConditionCheckerBuilder before(long timeout, TimeUnit unit) {
            this.timeout = timeout;
            timeoutUnit = unit;
            return this;
        }

        public ConditionCheckerBuilder before(long timeoutMillis) {
            timeout = timeoutMillis;
            timeoutUnit = TimeUnit.MILLISECONDS;
            return this;
        }

        public <T> ConditionCheckerBuilder that(T input, Predicate<? super T> predicate) {
            this.input = input;
            this.predicate = predicate;
            return this;
        }

        public ConditionCheckerBuilder that(final Callable<Boolean> condition) {
            this.input = null;
            this.predicate = new Predicate<Void>() {
                @Override
                public boolean apply(Void input) {
                    try {
                        return condition.call();
                    } catch (Exception e) {
                        logger.error("Evaluation of condition threw exception", e);
                        return false;
                    }
                }
            };
            return this;
        }

        @SuppressWarnings("unchecked")
        public void becomesTrue() {
            new ConditionChecker(input, (Predicate<Object>) predicate, period, periodUnit).await(timeout, timeoutUnit);
        }

        @SuppressWarnings("unchecked")
        public void becomesFalse() {
            this.predicate = Predicates.not(predicate);
            new ConditionChecker(input, (Predicate<Object>) predicate, period, periodUnit).await(timeout, timeoutUnit);
        }

    }

    private static final Logger logger = LoggerFactory.getLogger(ConditionChecker.class);

    public static ConditionCheckerBuilder check() {
        return new ConditionCheckerBuilder();
    }

    private final Object input;
    private final Predicate<Object> predicate;
    private final Lock lock;
    private final Condition condition;
    private final Timer timer;

    @SuppressWarnings("unchecked")
    public <T> ConditionChecker(T input, Predicate<? super T> predicate, long period, TimeUnit periodUnit) {
        this.input = input;
        this.predicate = (Predicate<Object>) predicate;
        lock = new ReentrantLock();
        condition = lock.newCondition();
        timer = new Timer("condition-checker", true);
        timer.schedule(new TimerTask() {
            @Override
            public void run() {
                checkCondition();
            }
        }, 0, periodUnit.toMillis(period));
    }

    /**
     * Waits until the predicate becomes true,
     * or a timeout occurs, whichever happens first.
     */
    public void await(long timeout, TimeUnit unit) {
        boolean interrupted = false;
        long nanos = unit.toNanos(timeout);
        lock.lock();
        try {
            while (!evalCondition()) {
                if (nanos <= 0L)
                    fail(String.format("Timeout after %s %s while waiting for condition", timeout, unit.toString().toLowerCase()));
                try {
                    nanos = condition.awaitNanos(nanos);
                } catch (InterruptedException e) {
                    interrupted = true;
                }
            }
        } finally {
            timer.cancel();
            if (interrupted)
                Thread.currentThread().interrupt();
        }
    }

    private void checkCondition() {
        lock.lock();
        try {
            if (evalCondition()) {
                condition.signal();
            }
        } finally {
            lock.unlock();
        }
    }

    private boolean evalCondition() {
        return predicate.apply(input);
    }

}