一文解析Synchronized

向右看齐 2023-05-28 06:56 17阅读 0赞

# 1 三个窗口卖50张票 #

## 1.1 TicketWindowRunnable ##

public class TicketWindowRunnable implements Runnable { 
        private int index = 1;
        private final static int MAX = 50;
        @Override
        public void run() { 
            while (true) { 
                if (index > MAX) { 
                    break;
                }
                try { 
                    Thread.sleep(50);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " 的号码是：" + index++);
            }
        }
    }

## 1.2 测试 ##

public class BankTest { 
        public static void main(String[] args) { 
            TicketWindowRunnable runnable=new TicketWindowRunnable();
            Thread t1=new Thread(runnable,"一号窗口");
            Thread t2=new Thread(runnable,"二号窗口");
            Thread t3=new Thread(runnable,"三号窗口");
            t1.start();
            t2.start();
            t3.start();
        }
    }

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# 2 synchronized #

关键字synchronized可以保证在同一时刻，只有一个线程可以执行某个方法或某个代码块。

## 2.1 修改TicketWindowRunnable ##

public class TicketWindowRunnable implements Runnable { 
        private int index = 1;
        private final static int MAX = 50;
        private final Object LOCK = new Object();
        @Override
        public void run() { 
            while (true) { 
                synchronized (LOCK) { 
                    if (index > MAX) { 
                        break;
                    }
                    try { 
                        Thread.sleep(50);
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                    System.out.println(Thread.currentThread().getName() + " 的号码是：" + index++);
                }
            }
        }
    }

## 2.2 测试 ##

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# 3 查看汇编 #

#编译
    javac -encoding UTF-8  TicketWindowRunnable.java
    #汇编
    javap -c TicketWindowRunnable.class

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# 4 synchronized应用方式 #

## 4.1 对象锁 ##

(1) 代码

public class SynchronizedTest { 
        public static void main(String[] args) { 
            ObjectSynchronized lock=new ObjectSynchronized();
            Thread t1=new Thread(lock::m1,"t1");
            Thread t2=new Thread(lock::m2,"t2");
            t1.start();
            t2.start();
        }
    }
    /** * 创建对象锁，锁同步方法快 */
    class ObjectSynchronized { 
        private final Object LOCK = new Object();
        public void m1(){ 
            synchronized (LOCK){ 
                System.out.println(Thread.currentThread().getName()+",invoke ObjectSynchronized m1 start");
                try { 
                    Thread.sleep(5*1000);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName()+",invoke ObjectSynchronized m1 end");
            }
        }
        public void m2(){ 
            synchronized (LOCK){ 
                System.out.println(Thread.currentThread().getName()+",invoke ObjectSynchronized m2 start");
                try { 
                    Thread.sleep(5*1000);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName()+",invoke ObjectSynchronized m2 end");
            }
        }
    }

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## 4.2 This锁 ##

public class SynchronizedTest { 
        public static void main(String[] args) { 
            ThisSynchronized lock = new ThisSynchronized();
            Thread t1 = new Thread(lock::m1, "t1");
            Thread t2 = new Thread(lock::m2, "t2");
            t1.start();
            t2.start();
        }
    }
    /** * 同步函数其实用到的锁就是 this 锁 */
    class ThisSynchronized { 
        public  synchronized  void m1() { 
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 start");
            try { 
                Thread.sleep(5 * 1000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 end");
        }
        public synchronized void m2() { 
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m2 start");
            try { 
                Thread.sleep(5 * 1000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m2 end");
        }
    }

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## 4.3 This锁和对象锁同时存在时 ##

public class SynchronizedTest { 
        public static void main(String[] args) { 
            ObjectAndThisSynchronized lock = new ObjectAndThisSynchronized();
            Thread t1 = new Thread(lock::m1, "t1");
            Thread t2 = new Thread(lock::m2, "t2");
            t1.start();
            t2.start();
        }
    }
    class ObjectAndThisSynchronized { 
        private final Object LOCK = new Object();
        public void m1() { 
            synchronized (LOCK) { 
                System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 start");
                try { 
                    Thread.sleep(5 * 1000);
                } catch (InterruptedException e) { 
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 end");
            }
        }
        public synchronized void m2() { 
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m2 start");
            try { 
                Thread.sleep(5 * 1000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m2 end");
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 5]

## 4.4 创建两个对象时 ##

public class SynchronizedTest { 
        public static void main(String[] args) { 
            ObjectAndThisSynchronized lock1 = new ObjectAndThisSynchronized();
            ObjectAndThisSynchronized lock2 = new ObjectAndThisSynchronized();
            Thread t1 = new Thread(lock1::m1, "t1");
            Thread t2 = new Thread(lock2::m1, "t2");
            t1.start();
            t2.start();
        }
    }
    
    class ObjectAndThisSynchronized { 
    
        public synchronized void m1() { 
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 start");
            try { 
                Thread.sleep(5 * 1000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 end");
        }
    }

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM0MTI1OTk5_size_16_color_FFFFFF_t_70 6]

## 4.5 static锁 ##

public class SynchronizedTest { 
        public static void main(String[] args) { 
            Thread t1=new Thread(StaticSynchronized::m1,"t1");
            Thread t2=new Thread(StaticSynchronized::m2,"t2");
            t1.start();
            t2.start();
        }
    }
    class StaticSynchronized { 
        public static synchronized void m1() { 
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 start");
            try { 
                Thread.sleep(5 * 1000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m1 end");
        }
        public static synchronized void m2() { 
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m2 start");
            try { 
                Thread.sleep(5 * 1000);
            } catch (InterruptedException e) { 
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + ",invoke ObjectSynchronized m2 end");
        }
    }

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# 5 死锁分析 #

public class DeadLock { 
        private static final Object LOCK1=new Object();
        private static final Object LOCK2=new Object();
        public static void main(String[] args) { 
            Thread t1=new Thread(()->{ 
                synchronized (LOCK1){ 
                    try { 
                        Thread.sleep(5*10);
                    } catch (InterruptedException e) { 
                        e.printStackTrace();
                    }
                    synchronized (LOCK2){ 
                    }
                }
            },"t1");
            Thread t2=new Thread(()->{ 
                synchronized (LOCK2){ 
                    synchronized (LOCK1){ 
                    }
                }
            },"t2");
            t1.start();
            t2.start();
        }
    }

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