詳解Java編程中線程同步和准時啟動線程的辦法。本站提示廣大學習愛好者：（詳解Java編程中線程同步和准時啟動線程的辦法）文章只能為提供參考，不一定能成為您想要的結果。以下是詳解Java編程中線程同步和准時啟動線程的辦法正文
應用wait()與notify()完成線程間協作
1. wait()與notify()/notifyAll()
挪用sleep()和yield()的時刻鎖並沒有被釋放，而挪用wait()將釋放鎖。如許另外一個義務（線程）可以取得以後對象的鎖，從而進入它的synchronized辦法中。可以經由過程notify()/notifyAll()，或許時光到期，從wait()中恢復履行。
只能在同步掌握辦法或同步塊中挪用wait()、notify()和notifyAll()。假如在非同步的辦法裡挪用這些辦法，在運轉時會拋出IllegalMonitorStateException異常。
2.模仿單個線程對多個線程的叫醒
模仿線程之間的協作。Game類有2個同步辦法prepare()和go()。標記位start用於斷定以後線程能否須要wait()。Game類的實例起首啟動一切的Athele類實例，使其進入wait()狀況，在一段時光後，轉變標記位並notifyAll()一切處於wait狀況的Athele線程。
Game.java
package concurrency;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
class Athlete implements Runnable {
private final int id;
private Game game;
public Athlete(int id, Game game) {
this.id = id;
this.game = game;
}
public boolean equals(Object o) {
if (!(o instanceof Athlete))
return false;
Athlete athlete = (Athlete) o;
return id == athlete.id;
}
public String toString() {
return "Athlete<" + id + ">";
}
public int hashCode() {
return new Integer(id).hashCode();
}
public void run() {
try {
game.prepare(this);
} catch (InterruptedException e) {
System.out.println(this + " quit the game");
}
}
}
public class Game implements Runnable {
private Set<Athlete> players = new HashSet<Athlete>();
private boolean start = false;
public void addPlayer(Athlete one) {
players.add(one);
}
public void removePlayer(Athlete one) {
players.remove(one);
}
public Collection<Athlete> getPlayers() {
return Collections.unmodifiableSet(players);
}
public void prepare(Athlete athlete) throws InterruptedException {
System.out.println(athlete + " ready!");
synchronized (this) {
while (!start)
wait();
if (start)
System.out.println(athlete + " go!");
}
}
public synchronized void go() {
notifyAll();
}
public void ready() {
Iterator<Athlete> iter = getPlayers().iterator();
while (iter.hasNext())
new Thread(iter.next()).start();
}
public void run() {
start = false;
System.out.println("Ready......");
System.out.println("Ready......");
System.out.println("Ready......");
ready();
start = true;
System.out.println("Go!");
go();
}
public static void main(String[] args) {
Game game = new Game();
for (int i = 0; i < 10; i++)
game.addPlayer(new Athlete(i, game));
new Thread(game).start();
}
}
成果：
Ready...... Ready...... Ready...... Athlete<0> ready! Athlete<1> ready! Athlete<2> ready! Athlete<3> ready! Athlete<4> ready! Athlete<5> ready! Athlete<6> ready! Athlete<7> ready! Athlete<8> ready! Athlete<9> ready! Go! Athlete<9> go! Athlete<8> go! Athlete<7> go! Athlete<6> go! Athlete<5> go! Athlete<4> go! Athlete<3> go! Athlete<2> go! Athlete<1> go! Athlete<0> go!
3.模仿忙期待進程
MyObject類的實例是被不雅察者，當不雅察事宜產生時，它會告訴一個Monitor類的實例（告訴的方法是轉變一個標記位）。而此Monitor類的實例是經由過程忙期待來赓續的檢討標記位能否變更。
BusyWaiting.java
import java.util.concurrent.TimeUnit;
class MyObject implements Runnable {
private Monitor monitor;
public MyObject(Monitor monitor) {
this.monitor = monitor;
}
public void run() {
try {
TimeUnit.SECONDS.sleep(3);
System.out.println("i'm going.");
monitor.gotMessage();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class Monitor implements Runnable {
private volatile boolean go = false;
public void gotMessage() throws InterruptedException {
go = true;
}
public void watching() {
while (go == false)
;
System.out.println("He has gone.");
}
public void run() {
watching();
}
}
public class BusyWaiting {
public static void main(String[] args) {
Monitor monitor = new Monitor();
MyObject o = new MyObject(monitor);
new Thread(o).start();
new Thread(monitor).start();
}
}
成果：
i'm going. He has gone.
4.應用wait()與notify()改寫下面的例子
上面的例子經由過程wait()來代替忙期待機制，當收到告訴新聞時，notify以後Monitor類線程。
Wait.java
package concurrency.wait;
import java.util.concurrent.TimeUnit;
class MyObject implements Runnable {
private Monitor monitor;
public MyObject(Monitor monitor) {
this.monitor = monitor;
}
准時啟動線程
這裡供給兩種在指准時間後啟動線程的辦法。一是經由過程java.util.concurrent.DelayQueue完成；二是經由過程java.util.concurrent.ScheduledThreadPoolExecutor完成。
1. java.util.concurrent.DelayQueue
類DelayQueue是一個無界壅塞隊列，只要在延遲期滿時能力從中提取元素。它接收完成Delayed接口的實例作為元素。
<<interface>>Delayed.java
package java.util.concurrent;
import java.util.*;
public interface Delayed extends Comparable<Delayed> {
long getDelay(TimeUnit unit);
}
getDelay()前往與此對象相干的殘剩延遲時光，以給定的時光單元表現。此接口的完成必需界說一個 compareTo 辦法，該辦法供給與此接口的 getDelay 辦法分歧的排序。
DelayQueue隊列的頭部是延遲期滿後保留時光最長的 Delayed 元素。當一個元素的getDelay(TimeUnit.NANOSECONDS) 辦法前往一個小於等於 0 的值時，將產生到期。
2.設計帶有時光延遲特征的隊列
類DelayedTasker保護一個DelayQueue<DelayedTask> queue，個中DelayedTask完成了Delayed接口，並由一個外部類界說。內部類和外部類都完成Runnable接口，關於內部類來講，它的run辦法是按界說的時光前後掏出隊列中的義務，而這些義務即外部類的實例，外部類的run辦法界說每一個線程詳細邏輯。
這個設計的本質是界說了一個具有時光特征的線程義務列表，並且該列表可所以隨意率性長度的。每次添加義務時指定啟動時光便可。
DelayedTasker.java
package com.zj.timedtask;
import static java.util.concurrent.TimeUnit.SECONDS;
import static java.util.concurrent.TimeUnit.NANOSECONDS;
import java.util.Collection;
import java.util.Collections;
import java.util.Random;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
public class DelayedTasker implements Runnable {
DelayQueue<DelayedTask> queue = new DelayQueue<DelayedTask>();
public void addTask(DelayedTask e) {
queue.put(e);
}
public void removeTask() {
queue.poll();
}
public Collection<DelayedTask> getAllTasks() {
return Collections.unmodifiableCollection(queue);
}
public int getTaskQuantity() {
return queue.size();
}
public void run() {
while (!queue.isEmpty())
try {
queue.take().run();
} catch (InterruptedException e) {
System.out.println("Interrupted");
}
System.out.println("Finished DelayedTask");
}
public static class DelayedTask implements Delayed, Runnable {
private static int counter = 0;
private final int id = counter++;
private final int delta;
private final long trigger;
public DelayedTask(int delayInSeconds) {
delta = delayInSeconds;
trigger = System.nanoTime() + NANOSECONDS.convert(delta, SECONDS);
}
public long getDelay(TimeUnit unit) {
return unit.convert(trigger - System.nanoTime(), NANOSECONDS);
}
public int compareTo(Delayed arg) {
DelayedTask that = (DelayedTask) arg;
if (trigger < that.trigger)
return -1;
if (trigger > that.trigger)
return 1;
return 0;
}
public void run() {
//run all that you want to do
System.out.println(this);
}
public String toString() {
return "[" + delta + "s]" + "Task" + id;
}
}
public static void main(String[] args) {
Random rand = new Random();
ExecutorService exec = Executors.newCachedThreadPool();
DelayedTasker tasker = new DelayedTasker();
for (int i = 0; i < 10; i++)
tasker.addTask(new DelayedTask(rand.nextInt(5)));
exec.execute(tasker);
exec.shutdown();
}
}
成果：
[0s]Task 1 [0s]Task 2 [0s]Task 3 [1s]Task 6 [2s]Task 5 [3s]Task 8 [4s]Task 0 [4s]Task 4 [4s]Task 7 [4s]Task 9 Finished DelayedTask
3. java.util.concurrent.ScheduledThreadPoolExecutor
該類可以另行支配在給定的延遲後運轉義務（線程），或許按期（反復）履行義務。在結構子中須要曉得線程池的年夜小。最重要的辦法是：
[1] schedule
public ScheduledFuture<?> schedule(Runnable command, long delay,TimeUnit unit)
創立並履行在給定延遲後啟用的一次性操作。
指定者：
-接口 ScheduledExecutorService 中的 schedule;
參數：
-command - 要履行的義務 ;
-delay - 從如今開端延遲履行的時光 ;
-unit - 延遲參數的時光單元 ;
前往：
-表現掛起義務完成的 ScheduledFuture，而且其 get() 辦法在完成後將前往 null。
[2] scheduleAtFixedRate
public ScheduledFuture<?> scheduleAtFixedRate(
Runnable command,long initialDelay,long period,TimeUnit unit)
創立並履行一個在給定初始延遲後初次啟用的按期操作，後續操作具有給定的周期；也就是將在 initialDelay 後開端履行，然後在 initialDelay+period 後履行，接著在 initialDelay + 2 * period 後履行，依此類推。假如義務的任何一個履行碰到異常，則後續履行都邑被撤消。不然，只能經由過程履行法式的撤消或終止辦法來終止該義務。假如此義務的任何一個履行要消費比其周期更長的時光，則將推延後續履行，但不會同時履行。
指定者：
-接口 ScheduledExecutorService 中的 scheduleAtFixedRate;
參數：
-command - 要履行的義務 ;
-initialDelay - 初次履行的延遲時光 ;
-period - 持續履行之間的周期 ;
-unit - initialDelay 和 period 參數的時光單元 ;
前往：
-表現掛起義務完成的 ScheduledFuture，而且其 get() 辦法在撤消後將拋出異常。
4.設計帶有時光延遲特征的線程履行者
類ScheduleTasked聯系關系一個ScheduledThreadPoolExcutor，可以指定線程池的年夜小。經由過程schedule辦法曉得線程及延遲的時光，經由過程shutdown辦法封閉線程池。關於詳細義務（線程）的邏輯具有必定的靈巧性（比擬前一中設計，前一種設計必需事前界說線程的邏輯，但可以經由過程繼續或裝潢修正線程詳細邏輯設計）。
ScheduleTasker.java
package com.zj.timedtask;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
public class ScheduleTasker {
private int corePoolSize = 10;
ScheduledThreadPoolExecutor scheduler;
public ScheduleTasker() {
scheduler = new ScheduledThreadPoolExecutor(corePoolSize);
}
public ScheduleTasker(int quantity) {
corePoolSize = quantity;
scheduler = new ScheduledThreadPoolExecutor(corePoolSize);
}
public void schedule(Runnable event, long delay) {
scheduler.schedule(event, delay, TimeUnit.SECONDS);
}
public void shutdown() {
scheduler.shutdown();
}
public static void main(String[] args) {
ScheduleTasker tasker = new ScheduleTasker();
tasker.schedule(new Runnable() {
public void run() {
System.out.println("[1s]Task 1");
}
}, 1);
tasker.schedule(new Runnable() {
public void run() {
System.out.println("[2s]Task 2");
}
}, 2);
tasker.schedule(new Runnable() {
public void run() {
System.out.println("[4s]Task 3");
}
}, 4);
tasker.schedule(new Runnable() {
public void run() {
System.out.println("[10s]Task 4");
}
}, 10);
tasker.shutdown();
}
}
成果：
[1s]Task 1
[2s]Task 2
[4s]Task 3
[10s]Task 4
public void run() {
try {
TimeUnit.SECONDS.sleep(3);
System.out.println("i'm going.");
monitor.gotMessage();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
class Monitor implements Runnable {
private volatile boolean go = false;
public synchronized void gotMessage() throws InterruptedException {
go = true;
notify();
}
public synchronized void watching() throws InterruptedException {
while (go == false)
wait();
System.out.println("He has gone.");
}
public void run() {
try {
watching();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public class Wait {
public static void main(String[] args) {
Monitor monitor = new Monitor();
MyObject o = new MyObject(monitor);
new Thread(o).start();
new Thread(monitor).start();
}
}
成果：
i'm going. He has gone.
