【Java多线程】JDK1.5并发包API杂谈

并发与并行

并发

一个或多个处理器执行更多的任务（通过划分时间片来执行更多的任务），从逻辑上实现同时运行：

如，N个并发请求在一个两核CPU上：

并行

N个处理器分别同时执行N个任务，从物理上实现同时运行：

线程互斥

阻塞地加锁，通过ReentrantLock.lock()阻塞地加锁

阻塞地加锁的意义，在于在多线程环境下，同一时刻只有一个线程执行加锁代码，其他线程阻塞在加锁代码之前。

ReentrantLock继承Lock，Lock接口提供了这些方法：

ReentrantLock与synchronized既相似，又有所不同，比如：

  • ReentrantLock支持公平和非公平加锁，synchronized只支持非公平加锁
  • ReentrantLock支持非阻塞地尝试获取锁，synchronized并不支持
  • ReentrantLock阻塞获取锁支持响应中断，而synchronized获取锁阻塞时不响应中断
package com.nicchagil.exercies.reentrantlock.lock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.logging.Logger;

public class LockExercise {
    
    private static Logger logger = Logger.getLogger(LockExercise.class.getName());
    private static Lock lock = new ReentrantLock();

    public static void main(String[] args) {

        new Thread(new Runnable() {
            @Override
            public void run() {
                lock.lock();
                try {
                    logger.info(Thread.currentThread().getName() + " run.");
                    
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                } finally {
                    lock.unlock();
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                lock.lock();
                try {
                    logger.info(Thread.currentThread().getName() + " run.");
                    
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                } finally {
                    lock.unlock();
                }
            }
        }).start();
        
    }

}

阻塞地加锁，通过synchronized阻塞地加锁

package com.nicchagil.exercies.reentrantlock.lock;

import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class SynchronizedExercise {
    
    private static Logger logger = Logger.getLogger(SynchronizedExercise.class.getName());
    private static Object obj = new Object();

    public static void main(String[] args) {

        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (obj) {
                    logger.info(Thread.currentThread().getName() + " run.");
                    
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (obj) {
                    logger.info(Thread.currentThread().getName() + " run.");
                    
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }).start();
        
    }

}

获取锁阻塞时能响应中断

ReentrantLock使用lockInterruptibly()阻塞获取锁时，能响应中断：

package com.nicchagil.exercies.reentrantlock.interruptibly;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.logging.Logger;

public class LockInterruptiblyExercise {
    
    private static Logger logger = Logger.getLogger(LockInterruptiblyExercise.class.getName());

    public static void main(String[] args) {
        Lock lock = new ReentrantLock(); // 声明可重入锁
        
        lock.lock(); // 阻塞获取锁
        logger.info("阻塞获取锁");
        try {
            
            Thread t1 = new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        lock.lockInterruptibly(); // 尝试获取锁
                    } catch (InterruptedException e) {
                        logger.info(Thread.currentThread().getName() + "获取锁被打断");
                    }
                }
            });
            t1.start();
            
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
            t1.interrupt(); // 打断线程
            
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
        } finally {
            lock.unlock(); // 释放锁
            logger.info("释放锁");
        }
    }

}

结果：

八月 01, 2017 1:59:33 下午 com.nicchagil.exercies.reentrantlock.interruptibly.LockInterruptiblyExercise main
信息: 阻塞获取锁
八月 01, 2017 1:59:36 下午 com.nicchagil.exercies.reentrantlock.interruptibly.LockInterruptiblyExercise$1 run
信息: Thread-1获取锁被打断
八月 01, 2017 1:59:39 下午 com.nicchagil.exercies.reentrantlock.interruptibly.LockInterruptiblyExercise main
信息: 释放锁

而synchronized阻塞获取锁时不响应中断：

package com.nicchagil.exercies.reentrantlock.interruptibly;

import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class SyncInterruptiblyExercise {
    
    private static Logger logger = Logger.getLogger(SyncInterruptiblyExercise.class.getName());
    private static Object obj = new Object();

    /**
     * 测试synchronized获取锁时被打断是否抛出InterruptedException
     * 结果：
     * 七月 12, 2017 9:30:42 下午 com.nicchagil.exercies.reentrantlock.interruptibly.SyncInterruptiblyExercise main
     * 信息: 阻塞获取锁
     * 七月 12, 2017 9:30:48 下午 com.nicchagil.exercies.reentrantlock.interruptibly.SyncInterruptiblyExercise main
     * 信息: 释放锁
     */
    public static void main(String[] args) {
        synchronized (obj) {
            logger.info("阻塞获取锁");
            
            Thread t1 = new Thread(new Runnable() {
                @Override
                public void run() {
                    try {
                        synchronized (obj) {
                            
                        }
                    } catch (Exception e) {
                        logger.info(Thread.currentThread().getName() + "获取锁被打断");
                    }
                }
            });
            t1.start();
            
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
            t1.interrupt(); // 打断线程
            
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
            logger.info("释放锁");
        }
    }

}

结果：

八月 01, 2017 2:01:11 下午 com.nicchagil.exercies.reentrantlock.interruptibly.SyncInterruptiblyExercise main
信息: 阻塞获取锁
八月 01, 2017 2:01:17 下午 com.nicchagil.exercies.reentrantlock.interruptibly.SyncInterruptiblyExercise main
信息: 释放锁

读写锁，ReentrantReadWriteLock

加上写锁后，无论读锁还是写锁均堵塞：

package com.nicchagil.exercies.reentrantreadwritelock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.logging.Logger;

public class ReentrantReadWriteLockWriteLockExercise {
    
    private static Logger logger = Logger.getLogger(ReentrantReadWriteLockWriteLockExercise.class.getName());
    
    private static ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();

    public static void main(String[] args) {
        
        /* 先加写锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.writeLock().lock();
                logger.info(Thread.currentThread().getName() + "加写锁");
                try {
                    TimeUnit.SECONDS.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.writeLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解写锁");
                }
            }
        }).start();
        
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        
        /* 然后加写锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.writeLock().lock();
                logger.info(Thread.currentThread().getName() + "加写锁");
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.writeLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解写锁");
                }
            }
        }).start();
        
        /* 然后加读锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.readLock().lock();
                logger.info(Thread.currentThread().getName() + "加读锁");
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.readLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解读锁");
                }
            }
        }).start();
        
    }

}

结果：

八月 01, 2017 1:42:44 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockWriteLockExercise$1 run
信息: Thread-1加写锁
八月 01, 2017 1:42:54 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockWriteLockExercise$1 run
信息: Thread-1解写锁
八月 01, 2017 1:42:54 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockWriteLockExercise$2 run
信息: Thread-2加写锁
八月 01, 2017 1:42:57 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockWriteLockExercise$2 run
信息: Thread-2解写锁
八月 01, 2017 1:42:57 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockWriteLockExercise$3 run
信息: Thread-3加读锁
八月 01, 2017 1:43:00 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockWriteLockExercise$3 run
信息: Thread-3解读锁

获取读锁后，再获取读锁不堵塞，但获取写锁堵塞：

package com.nicchagil.exercies.reentrantreadwritelock;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.logging.Logger;

public class ReentrantReadWriteLockReadLockExercise {
    
    private static Logger logger = Logger.getLogger(ReentrantReadWriteLockReadLockExercise.class.getName());
    
    private static ReentrantReadWriteLock reentrantReadWriteLock = new ReentrantReadWriteLock();

    public static void main(String[] args) {
        
        /* 先加读锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.readLock().lock();
                logger.info(Thread.currentThread().getName() + "加读锁");
                try {
                    TimeUnit.SECONDS.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.readLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解读锁");
                }
            }
        }).start();
        
        try {
            TimeUnit.SECONDS.sleep(1);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        
        /* 然后加读锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.readLock().lock();
                logger.info(Thread.currentThread().getName() + "加读锁");
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.readLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解读锁");
                }
            }
        }).start();
        
        /* 然后加写锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.writeLock().lock();
                logger.info(Thread.currentThread().getName() + "加写锁");
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.writeLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解写锁");
                }
            }
        }).start();
        
        /* 然后加读锁 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                reentrantReadWriteLock.readLock().lock();
                logger.info(Thread.currentThread().getName() + "加读锁");
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                } finally {
                    reentrantReadWriteLock.readLock().unlock();
                    logger.info(Thread.currentThread().getName() + "解读锁");
                }
            }
        }).start();
        
    }

}

结果：

八月 01, 2017 1:44:06 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$1 run
信息: Thread-1加读锁
八月 01, 2017 1:44:07 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$2 run
信息: Thread-2加读锁
八月 01, 2017 1:44:10 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$2 run
信息: Thread-2解读锁
八月 01, 2017 1:44:16 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$1 run
信息: Thread-1解读锁
八月 01, 2017 1:44:16 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$3 run
信息: Thread-3加写锁
八月 01, 2017 1:44:19 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$3 run
信息: Thread-3解写锁
八月 01, 2017 1:44:19 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$4 run
信息: Thread-4加读锁
八月 01, 2017 1:44:22 下午 com.nicchagil.exercies.reentrantreadwritelock.ReentrantReadWriteLockReadLockExercise$4 run
信息: Thread-4解读锁

阻塞与唤醒（线程间交互）

指定线程的阻塞与唤醒，LockSupport.park(Object blocker)

使用LockSupport.park()：

package com.nicchagil.exercies.locksupportpart;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;
import java.util.logging.Logger;

public class PartUnpartExercise {
    
    private static Logger logger = Logger.getLogger(PartUnpartExercise.class.getName());

    public static void main(String[] args) {
        Thread mainThread = Thread.currentThread();
        
        /* 其他线程在30S后唤醒主线程 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(30);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                LockSupport.unpark(mainThread); // 唤醒
                logger.info(Thread.currentThread().getName() + "唤醒" + mainThread.getName());
            }
        }).start();
        
        logger.info(Thread.currentThread().getName() + "准备被阻塞");
        LockSupport.park(); // 阻塞
        logger.info(Thread.currentThread().getName() + "被唤醒，开始执行");
    }

}

使用LockSupport.park(Object blocker)：

package com.nicchagil.exercies.locksupportpart;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.LockSupport;
import java.util.logging.Logger;

public class MyPartUnpartExercise {
    
    private static Logger logger = Logger.getLogger(MyPartUnpartExercise.class.getName());
    private static Object object = new Object();

    public static void main(String[] args) {
        Thread mainThread = Thread.currentThread();
        
        /* 其他线程在30S后唤醒主线程 */
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(30);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                LockSupport.unpark(mainThread); // 唤醒
                logger.info(Thread.currentThread().getName() + "唤醒" + mainThread.getName());
            }
        }).start();
        
        logger.info(Thread.currentThread().getName() + "准备被阻塞");
        LockSupport.park(object); // 阻塞
        logger.info(Thread.currentThread().getName() + "被唤醒，开始执行");
    }

}

LockSupport.park()与LockSupport.park(Object blocker)区别在于阻塞时是否有标识等待的对象，后者是JDK6添加的，可传入等待的对象。用jstack工具生成的线程快照的对比可见下图：

获得锁的线程阻塞和唤醒，Condition.await()、Condition.signal()或Object.wait()、Object.notify()

在获取锁的情况下，线程阻塞和唤醒可分别使用Condition.await()、Condition.signal()，如果在没获得前下调用，会报异常java.lang.IllegalMonitorStateException。

package com.nicchagil.exercies.condition;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.logging.Logger;

public class ReentrantLockConditionExercise {
    
    private static Logger logger = Logger.getLogger(ReentrantLockConditionExercise.class.getName());
    
    private static volatile boolean flag = false;
    
    public static void main(String[] args) {
        Lock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                lock.lock();
                
                try {
                    while (!flag) {
                        logger.info(Thread.currentThread().getName() + "继续等待（条件还不成熟）");
                        condition.await(); // 等待其他线程改变当前线程需要的条件（会释放锁）
                    }
                    logger.info(Thread.currentThread().getName() + "继续业务（条件已成熟）");
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } finally {
                    lock.unlock();
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                lock.lock();
                
                try {
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    
                    logger.info(Thread.currentThread().getName() + "开始改变数据");
                    flag = true;
                    condition.signal(); // 唤醒其他线程（释放锁）
                    logger.info(Thread.currentThread().getName() + "改变数据完毕，并通知其它线");
                } finally {
                    lock.unlock();
                }
            }
        }).start();
        
    }

}

当然，也可使用Object.wait()、Object.notify()实现此功能。

package com.nicchagil.exercies.condition.waitnotify;

import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

import com.nicchagil.exercies.condition.ReentrantLockConditionExercise;

public class WaitNotifyExercise {
    
    /*
     * 内部类，封装boolean（不直接用Boolean，因为唤醒前改变数值时使用“flag = true”会修改flag的对象，导致用没加锁的对象调用“notify()”从而报异常）
     */
    static class MyFlag {
        private Boolean flag = false;

        public Boolean getFlag() {
            return flag;
        }

        public void setFlag(Boolean flag) {
            this.flag = flag;
        }
    }

    private static Logger logger = Logger.getLogger(ReentrantLockConditionExercise.class.getName());

    private static volatile MyFlag myFlag = new MyFlag();
    
    public static void main(String[] args) {
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (myFlag) {
                    try {
                        while (!myFlag.getFlag()) {
                            logger.info(Thread.currentThread().getName() + "继续等待（条件还不成熟）");
                            myFlag.wait(); // 等待其他线程改变当前线程需要的条件（会释放锁）
                        }
                        logger.info(Thread.currentThread().getName() + "继续业务（条件已成熟）");
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }).start();
        
        new Thread(new Runnable() {
            @Override
            public void run() {
                synchronized (myFlag) {
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    
                    logger.info(Thread.currentThread().getName() + "开始改变数据");
                    myFlag.setFlag(true);
                    myFlag.notify(); // 唤醒其他线程（释放锁）
                    logger.info(Thread.currentThread().getName() + "改变数据完毕，并通知其它线");
                }
            }
        }).start();
        
    }

}

等待其它线程结束，CountDownLatch.countDown()、CountDownLatch.await()

常见场景，比如A、B、C三个业务逻辑，3个业务之间没有依赖，可以并行运行，3个业务都执行完毕后向前端反馈结果。
一个线程等待其他线程结束才继续运行，可以用CountDownLatch.countDown()、CountDownLatch.await()或CyclicBarrier.await()或Thread.join()。

当一个线程的业务执行完，使用CountDownLatch.countDown()减1个任务，在一个线程中使用CountDownLatch.await()等待任务数减至0：

package com.nicchagil.exercies.countdownlatch;

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class CountDownLatchExercise {
    
    private static Logger logger = Logger.getLogger(CountDownLatchExercise.class.getName());
    
    private static CountDownLatch countDownLatch = new CountDownLatch(2);

    public static void main(String[] args) throws InterruptedException {
        logger.info(Thread.currentThread().getName() + " start..."); // 主任务开始
        
        ExecutorService executorService = Executors.newCachedThreadPool();
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                logger.info(Thread.currentThread().getName() + " complete..."); // 子任务一完成
                countDownLatch.countDown();
            }
        });
        
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                logger.info(Thread.currentThread().getName() + " complete..."); // 子任务二完成
                countDownLatch.countDown();
            }
        });
        
        countDownLatch.await();
        logger.info(Thread.currentThread().getName() + " complete..."); // 主任务完成
    }

}

等待其它线程结束，CyclicBarrier.await()

各线程执行完毕都使用CyclicBarrier.await()，表示到达Barrier（屏障）。另外CyclicBarrier与CountDownLatch的区别还有，前者可通过cyclicBarrier.reset()重置数值，可通过构造方式CyclicBarrier(int parties, Runnable barrierAction)声明当屏障要被越过时由最后到达屏障的线程执行barrierAction任务:

package com.nicchagil.exercies.cyclicbarrier;

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

import com.nicchagil.exercies.countdownlatch.CountDownLatchExercise;

public class CyclicBarrierExercise {
    
    private static Logger logger = Logger.getLogger(CountDownLatchExercise.class.getName());
    
    private static CyclicBarrier cyclicBarrier = new CyclicBarrier(3);

    public static void main(String[] args) {
        logger.info(Thread.currentThread().getName() + " start..."); // 主任务开始
        
        ExecutorService executorService = Executors.newCachedThreadPool();
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                logger.info(Thread.currentThread().getName() + " complete..."); // 子任务一完成
                try {
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        
        executorService.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                logger.info(Thread.currentThread().getName() + " complete..."); // 子任务二完成
                try {
                    cyclicBarrier.await();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (BrokenBarrierException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        });
        
        try {
            cyclicBarrier.await();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        logger.info(Thread.currentThread().getName() + " complete..."); // 主任务完成
    }

}

等待join()的线程完成，Thread.join()

使用Thread.join()：

package com.nicchagil.exercies.countdownlatch.joinimplement;

import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class JoinExercise {
    
    private static Logger logger = Logger.getLogger(JoinExercise.class.getName());
    
    public static void main(String[] args) {
        logger.info(Thread.currentThread().getName() + " start..."); // 主任务开始
        
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(3);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                logger.info(Thread.currentThread().getName() + " complete..."); // 子任务一完成
            }
        });
        
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    TimeUnit.SECONDS.sleep(5);
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                
                logger.info(Thread.currentThread().getName() + " complete..."); // 子任务二完成
            }
        });
        
        t1.start();
        t2.start();
        
        /* 插入主线程，让主线程等待其完成 */
        try {
            t1.join();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        try {
            t2.join();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        logger.info(Thread.currentThread().getName() + " complete..."); // 主任务完成
    }

}

线程睡眠，Thread.sleep(long millis)或TimeUnit.sleep(long timeout)

常用此俩方法可使线程睡眠，但不会释放锁。

使用Thread.sleep(long millis)：

package com.nicchagil.exercies.threadsleep;

import java.util.logging.Logger;

public class ThreadSleep {
    
    private static Logger logger = Logger.getLogger(ThreadSleep.class.getName());

    public static void main(String[] args) {
        logger.info("开始睡眠");
        
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        logger.info("结束睡眠");
    }

}

使用TimeUnit.sleep(long timeout)：

package com.nicchagil.exercies.threadsleep;

import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class TimeUnitThreadSleep {
    
    private static Logger logger = Logger.getLogger(TimeUnitThreadSleep.class.getName());

    public static void main(String[] args) {
        logger.info("开始睡眠");
        
        try {
            TimeUnit.SECONDS.sleep(3);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        logger.info("结束睡眠");
    }

}

狭路相逢勇者胜，同一时间限制指定数量的线程访问，Semaphore

在多线程环境，某些资源是有限的，比如文件IO、数据库连接，我们需要作流量控制，可以使用Semaphore.acquire()获取一个许可，Semaphore.release()释放一个许可：

package com.nicchagil.exercies.semaphore;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class SemaphoreExercise {
    
    private static Logger logger = Logger.getLogger(SemaphoreExercise.class.getName());
    
    private static Semaphore semaphore = new Semaphore(3); // 最多同时通过3个信号的信号量

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newCachedThreadPool();
        
        for (int i = 0; i <= 10; i++) {
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    try {
                        semaphore.acquire(); // 获取一个信号
                    } catch (InterruptedException e1) {
                        // TODO Auto-generated catch block
                        e1.printStackTrace();
                    }
                    
                    /* 睡眠3S */
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    
                    logger.info(Thread.currentThread().getName() + " run...");
                    
                    semaphore.release(); // 释放一个信号
                }
            });
        }
        
    }

}

用数据库连接作为受限资源，同时最多只放行3个线程：

也许你会说，我一开始声明受限的线程数量就可以了，比如启动3个线程数（如下图）。但是，并非所有情况均如你所愿，比如线程不是由你启动的，由Servlet容器启动的呢；再比如，在数据库访问前有部分业务操作，这些操作比访问数据库耗时些，多启动些线程能增大吞吐量。

缓存线程，线程池，ExecutorService、Executors、ThreadPoolExecutor

将线程缓存起来重复利用，可以减低线程创建、销毁的成本，还可以对其进行管理。比如系统中线程的数量是有限的，不能无止境的创建。

线程池执行器，ThreadPoolExecutor

我们常用的Executors.newFixedThreadPool(int)、Executors.newCachedThreadPool()都是基于ThreadPoolExecutor，所以，先讲后者。

构造方法ThreadPoolExecutor(int corePoolSize, int maximumPoolSize, long keepAliveTime, TimeUnit unit, BlockingQueue<Runnable> workQueue)的参数分别为：

  1. corePoolSize，核心线程池线程的数量
  2. maximumPoolSize，总线程池线程的最大数量
  3. keepAliveTime，当总线程池中除了核心线程池的线程空闲时保持等待时间，超过此时间就回收此线程
  4. unit，keepAliveTime时间的单位
  5. workQueue，当提交的线程数超过核心线程池线程数量，线程在此队列中排队
  • 提交线程，优先在核心线程池中创建线程执行
  • 如果核心线程池已满，则在队列中排队待执行
  • 如果队列已满，则在总线程池创建线程执行
  • 如果总线程池也满了，则调用RejectedExecutionHandler（拒绝执行处理器）
package com.nicchagil.exercies.threadpool;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class ThreadPoolExecutorExercise {
    
    private static Logger logger = Logger.getLogger(ThreadPoolExecutorExercise.class.getName());

    public static void main(String[] args) {
        /* 核心线程池为3，最大线程池位6，链式堵塞队列长度为2 */
        ExecutorService executorService = new ThreadPoolExecutor(3, 6, 60L, TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(2));
        
        for (int i = 0; i <= 10; i++) {
            try {
                executorService.execute(new Runnable() {
                    @Override
                    public void run() {
                        logger.info(Thread.currentThread().getName() + "开始运行");
                        
                        try {
                            TimeUnit.SECONDS.sleep(5);
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                    }
                });
            } catch (Exception e) {
                logger.info("第几个线程提交失败：" + i);
            }
        }
    }

}

结果如下：

七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-1开始运行
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-5开始运行
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-2开始运行
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-4开始运行
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-3开始运行
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-6开始运行
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise main
信息: 第几个线程提交失败：8
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise main
信息: 第几个线程提交失败：9
七月 16, 2017 1:42:54 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise main
信息: 第几个线程提交失败：10
七月 16, 2017 1:42:59 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-5开始运行
七月 16, 2017 1:42:59 下午 com.nicchagil.exercies.threadpool.ThreadPoolExecutorExercise$1 run
信息: pool-1-thread-2开始运行

用指定数量的线程执行任务，Executors.newFixedThreadPool(int)

Executors.newFixedThreadPool(int)，实际上是new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())，可知：

  • 核心线程池、总线程池大小为nThreads
  • 总线程池空闲线程不等待（实际上因核心线程池、总线程池大小相等，总线程池也没有额外的线程了）
  • 使用链式堵塞队列，其最大容量为Integer.MAX_VALUE，可以视为无限吧（你提交2的31次方-1个任务试试？）
package com.nicchagil.exercies.threadpool;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class NewFixedThreadPoolExercise {
    
    private static Logger logger = Logger.getLogger(NewFixedThreadPoolExercise.class.getName());
    
    public static void main(String[] args) {
        // = new ThreadPoolExecutor(nThreads, nThreads, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>())
        ExecutorService executorService = Executors.newFixedThreadPool(3);
        
        // = new FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue<Runnable>()))
        // Executors.newSingleThreadExecutor();
        
        for (int i = 0; i <= 10; i++) {
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    logger.info(Thread.currentThread().getName() + "开始运行");
                    
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            });
        }
    }

}

用动态缓存的线程执行任务，Executors.newCachedThreadPool()

Executors.newCachedThreadPool()，实际上是new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>())，可知：

  • 核心线程数为0，总线程数为Integer.MAX_VALUE，可视为无限吧
  • 总线程池空闲线程等待新任务60秒，超时回收线程
  • 使用同步队列。此队列特点为，无容量；总线程池空闲线程调用SynchronousQueue.poll(long timeout, TimeUnit unit)在指定时间内等待新任务，如果总线程池没有空闲线程，则在总线程池中创建新线程，而总线程池的容量又可视为无限的，所以提交任务的速度大于执行任务的速度，会创建大量线程，导致CPU耗尽，内存溢出。
package com.nicchagil.exercies.threadpool;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.logging.Logger;

public class NewCachedThreadPoolExercise {
    
    private static Logger logger = Logger.getLogger(NewCachedThreadPoolExercise.class.getName());
    
    public static void main(String[] args) {
        // = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60L, TimeUnit.SECONDS, new SynchronousQueue<Runnable>())
        ExecutorService executorService = Executors.newCachedThreadPool();
        
        for (int i = 0; i <= 10; i++) {
            executorService.execute(new Runnable() {
                @Override
                public void run() {
                    logger.info(Thread.currentThread().getName() + "开始运行");
                    
                    try {
                        TimeUnit.SECONDS.sleep(3);
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            });
        }
    }

}
【推广】 免费学中医，健康全家人
原文地址：https://www.cnblogs.com/nick-huang/p/7153189.html