Callable和Runnable
Callable和Runnable的区别在于前者执行线程任务后是可以返回值。
package com.accat.concurrency.example.aqs;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
@Slf4j
public class FutureExample {
static class MyCallable implements Callable<String> {
@Override
public String call() throws Exception {
log.info("do something in callable");
Thread.sleep(5000);
return "Done";
}
}
public static void main(String[] args) throws Exception {
ExecutorService executorService = Executors.newCachedThreadPool();
Future<String> future = executorService.submit(new MyCallable());
log.info("do something in main");
Thread.sleep(1000);
String result = future.get();
log.info("result：{}", result);
}
}
FutureTask
FutureTask和Callable关系相当于Thread和Runnable的关系
前者支持返回值提取和状态获取。
package com.accat.concurrency.example.aqs;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.Callable;
import java.util.concurrent.FutureTask;
@Slf4j
public class FutureTaskExample {
public static void main(String[] args) throws Exception {
FutureTask<String> futureTask = new FutureTask<>(() -> {
log.info("do something in callable");
Thread.sleep(5000);
return "Done";
});
new Thread(futureTask).start();
log.info("do something in main");
Thread.sleep(1000);
log.info("waiting result");
String result = futureTask.get(); // 阻塞并获取结果
log.info("result：{}", result);
}
}
Fork/Join 框架
Fork切分大任务， 得出小结果集；
Join合并小结果集，得出最终结果；
采用工作窃取算法，避免线程竞争。工作窃取算法，当线程工作完后去窃取其他任务来进行执行
package com.accat.concurrency.example.aqs;
import lombok.extern.slf4j.Slf4j;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
@Slf4j
public class ForkJoinTaskExample extends RecursiveTask<Integer> {
public static final int threshold = 2;
private int start;
private int end;
public ForkJoinTaskExample(int start, int end) {
this.start = start;
this.end = end;
}
@Override
protected Integer compute() {
int sum = 0;
//如果任务足够小就计算任务
boolean canCompute = (end - start) <= threshold;
if (canCompute) {
for (int i = start; i <= end; i++) {
sum += i;
}
} else {
// 如果任务大于阈值，就分裂成两个子任务计算
int middle = (start + end) / 2;
ForkJoinTaskExample leftTask = new ForkJoinTaskExample(start, middle);
ForkJoinTaskExample rightTask = new ForkJoinTaskExample(middle + 1, end);
// 执行子任务
leftTask.fork();
rightTask.fork();
// 等待任务执行结束合并其结果
int leftResult = leftTask.join();
int rightResult = rightTask.join();
// 合并子任务
sum = leftResult + rightResult;
}
return sum;
}
public static void main(String[] args) {
ForkJoinPool forkjoinPool = new ForkJoinPool();
//生成一个计算任务，计算1+2+3+4
ForkJoinTaskExample task = new ForkJoinTaskExample(1, 100);
//执行一个任务
Future<Integer> result = forkjoinPool.submit(task);
try {
log.info("result:{}", result.get());
} catch (Exception e) {
log.error("exception", e);
}
}
}
AQS组件 - BlockingQueue
阻塞队列
提供的四套方法，当操作无法进行则做出相应的操作
ArrayBlockingQueue 有界数组实现的阻塞队列
DelayQueue 使用PriorityQueue优先队列和ReentrantLock锁实现的延迟队列
LinkedBlockingDeque 双端链表实现的阻塞队列
PriorityBlockingQueue 无界可排序的阻塞队列
SynchronousQueue 内部仅支持一个元素存取的同步队列
