前言:
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首先第一个问题,为什么进行线程同步和线程互斥?
最开始我们的操作系统的作业的调度单位是进程,但是由于每个进程都单独占据一个资源,而且进程的形态转换非常的耗费系统资源。
为了系统的调度更加轻量级,能够更好的支持并发,因此引入了线程这个概念。
PS:进程和线程的关系:线程是进程的一个实体同一进程内的不同线程共享该进程的系统资源
所以问题的答案来了,因为同一进程内的不同线程共享该进程的系统资源,这就导致了资源竞争的问题, 为了能够解决这个问题,所以引入了线程互斥,就是为了能够在单位时间内只有一个线程共享该进程的系统资源 。而 进程同步就是让多个线程合理有序的访问该进程的系统资源。2 What?
什么是线程同步?什么是线程互斥?
线程同步和线程互斥,类似于进程同步和进程互斥,在《操作系统》这本书中有另一个好听的名字:直接制约和间接制约
直接制约(同步关系):
某些应用程序,为了完成某个任务而建立了两个或多个进程(源于进程间的合作)。
间接制约(互斥关系):
多个程序并发执行时,由于共享系统资源(如CUP、I/O设备等)而导致这些并发执行的程序之间形成相互的制约
的关系。
因此,我们知道了线程同步和线程互斥的关系:
互斥是指某一资源同时只允许一个访问者对其进行访问,具有唯一性和排它性,访问是无序的。同步是指在互斥的基础上,通过其它机制实现访问者对资源的有序访问。同步其实已经实现了互斥,所以同步是一种更为复杂的互斥。互斥是一种特殊的同步。3 How?
Java如何实现线程同步和线程互斥?
先说简单的,Java实现线程互斥:无线程互斥的情况:
/** * @desc: 没有进行互斥的情况 * @author: YanMingXin * @create: 2021/12/19-18:02 **/public class Method0 { private int value = 10; private void reduce() { try { while (value == 0) { System.out.println("stop..."); return; } System.out.println(Thread.currentThread().getName() + ":" + value); value--; } catch (Exception e) { e.printStackTrace(); } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(3, 5, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 20; i++) { poolExecutor.execute(() -> { reduce(); }); } } public static void main(String[] args) { Method0 methodA = new Method0(); methodA.make(); }}方式一:互斥锁synchronized
/** * @desc: 互斥方式一 * @author: YanMingXin * @create: 2021/12/19-17:48 **/public class MethodA { private int value = 10; private synchronized void reduce() { try { while (value == 0) { System.out.println("stop..."); return; } System.out.println(Thread.currentThread().getName() + ":" + value); value--; } catch (Exception e) { e.printStackTrace(); } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(3, 5, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 20; i++) { poolExecutor.execute(() -> { reduce(); }); } } public static void main(String[] args) { MethodA methodA = new MethodA(); methodA.make(); }}方式二:可重入互斥锁ReentrantLock
/** * @desc: 互斥方式二 * @author: YanMingXin * @create: 2021/12/19-17:50 **/public class MethodB { private int value = 10; private ReentrantLock lock=new ReentrantLock(); private void reduce(){ lock.lock(); try { while (value == 0) { System.out.println("stop..."); return; } System.out.println(Thread.currentThread().getName() + ":" + value); value--; } catch (Exception e) { e.printStackTrace(); }finally { lock.unlock(); } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(3, 5, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 20; i++) { poolExecutor.execute(() -> { reduce(); }); } } public static void main(String[] args) { MethodB methodA = new MethodB(); methodA.make(); }}然后,Java实现线程同步:无线程同步的情况:
/** * @desc: 无线程同步状态 * @author: YanMingXin * @create: 2021/12/19-17:47 **/public class Method0 { private int value = 0; private static List list = new ArrayList<String>(); static { list = Arrays.asList("1-Insert", "2-Delete", "3-Update", "4-Select"); } private void reduce() { try { System.out.println(list.get(value)); value++; while (value > 3) { System.out.println("stop..."); return; } } catch (Exception e) { e.printStackTrace(); } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor( 4, 4, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 4; i++) { poolExecutor.execute(() -> { reduce(); }); } poolExecutor.shutdown(); } public static void main(String[] args) { Method0 methodA = new Method0(); methodA.make(); }}方式一:synchronized进行线程同步
/** * @desc: 线程同步方式一 * @author: YanMingXin * @create: 2021/12/19-17:47 **/public class MethodA { private int value = 0; private static List list = new ArrayList<String>(); static { list = Arrays.asList("1-Insert", "2-Delete", "3-Update", "4-Select"); } private synchronized void reduce() { try { System.out.println(list.get(value)); value++; while (value > 3) { System.out.println("stop..."); return; } } catch (Exception e) { e.printStackTrace(); } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor( 4, 4, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 4; i++) { poolExecutor.execute(() -> { reduce(); }); } poolExecutor.shutdown(); } public static void main(String[] args) { MethodA methodA = new MethodA(); methodA.make(); }}方式二:ReentrantLock进行线程同步
/** * @desc: 线程同步方式二 * @author: YanMingXin * @create: 2021/12/19-17:47 **/public class MethodA { private int value = 0; private ReentrantLock lock = new ReentrantLock(); private static List list = new ArrayList<String>(); static { list = Arrays.asList("1-Insert", "2-Delete", "3-Update", "4-Select"); } private void reduce() { lock.lock(); try { System.out.println(list.get(value)); value++; while (value > 3) { System.out.println("stop..."); return; } } catch (Exception e) { e.printStackTrace(); } finally { lock.unlock(); } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor( 4, 4, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 4; i++) { poolExecutor.execute(() -> { reduce(); }); } poolExecutor.shutdown(); } public static void main(String[] args) { MethodA methodA = new MethodA(); methodA.make(); }}方式三:synchronized代码块
/** * @desc: 线程同步方式三 * @author: YanMingXin * @create: 2021/12/19-17:47 **/public class MethodA { private int value = 0; private static List list = new ArrayList<String>(); static { list = Arrays.asList("1-Insert", "2-Delete", "3-Update", "4-Select"); } private void reduce() { synchronized (this) { try { System.out.println(list.get(value)); value++; while (value > 3) { System.out.println("stop..."); return; } } catch (Exception e) { e.printStackTrace(); } } } private void make() { ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor( 4, 4, 3, TimeUnit.SECONDS, new LinkedBlockingDeque<>()); for (int i = 0; i < 4; i++) { poolExecutor.execute(() -> { reduce(); }); } poolExecutor.shutdown(); } public static void main(String[] args) { MethodA methodA = new MethodA(); methodA.make(); }}
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