Mind mapping:
a Lock Interface
1.1 Lock Interface Overview
lock is to control access to shared resources by multiple threads tools. Typically, the lock provides exclusive access to shared resources: Only one thread can acquire the lock and all access to shared resources are required to first obtain a lock. However, some locks may allow concurrent access to shared resources, such as the read-write lock ReadWriteLock.
Before Lock interface goes, Java program is realized by the synchronized keyword lock function. After contracting in JDK1.5 and added Lock interface and associated implementation class to implement the lock function.
Although synchronized methods and scope of the mechanisms statements makes it easier to monitor lock program, and helps avoid many common programming errors involving locks, but sometimes you need a more flexible approach to the lock. For example, some algorithms for traversing the data structure requires the use of concurrent access to the "manual" or "chain lock": the locking You Get the node A, and then acquires a node B, A and acquire C and then released, and then release the B and D and the like obtained . In this scenario, the synchronized keyword is not so easy to implement, and easy to use Lock many interfaces.
Lock interface implementation class:
ReentrantLock, ReentrantReadWriteLock.ReadLock, ReentrantReadWriteLock.WriteLock
Simple use of 1.2 Lock
Lock lock=new ReentrantLock()；
lock.lock();
try{
}finally{
lock.unlock();
}
Lock because it is bound to the interface implementation class when it is used, in addition to release the lock object finall statement block is to ensure that after the lock is acquired, it can be finally released.
Note: best not to get locked in the process of writing the try block, because if an exception occurs while getting the lock, the exception thrown will also lead to the lock can not be released.
1.3 Lock characteristics of the interface and common methods
Lock interface provides synchronized keyword does not have the main features:
| characteristic | description |
|---|---|
| Non-blocking attempt to acquire the lock | The current thread tries to acquire the lock, if this time the lock is not acquired by another thread that holds the lock is successfully acquired and |
| Can interrupt access to the lock | Get to lock the thread can interrupt response, when the acquired lock the thread is interrupted, interrupt exception will be thrown, while the lock is released |
| Timeout acquire locks | Acquire a lock before the specified deadline, more than after the deadline still can not get the return |
Lock Interface basic methods:
| Method name | description |
|---|---|
| void lock() | Get the lock. If the lock is not available, the current thread will be disabled for thread scheduling purposes and lies dormant until it acquires the lock. |
| void lockInterruptibly() | Acquiring the lock, if available and returns immediately. If the lock is not available, then the current thread will be disabled to thread scheduling, and a dormant state, and lock () method is different from the lock may be acquired interrupts the current thread (corresponding interrupt). |
| Condition newCondition() | Gets waiting for a notification component that locks the binding and the current, the current thread only get a lock before calling the component wait () method, and after the call, the current thread releases the lock. |
| boolean tryLock() | Only you can get locked in when called. If available, the lock is acquired, and immediately returns true; if the lock is not available, this method will return immediately to false. |
| boolean tryLock(long time, TimeUnit unit) | Timeout acquire the lock in the current thread returns about three situations: 1. The current thread to acquire the lock within the timeout; 2 current thread is interrupted within the timeout period; 3 timeout ends and returns false... |
| void unlock() | Release the lock. |
Two Lock interface implementation class: ReentrantLock
ReentrantLock synchronized keyword and the same can be used to implement mutual exclusion synchronization between threads, but the function is more powerful and more flexible than the synchronized keyword.
ReentrantLock class A common method:
Construction method:
| Method name | description |
|---|---|
| ReentrantLock() | Create an instance of ReentrantLock. |
| ReentrantLock(boolean fair) | Create an instance of a particular type of lock (lock fair / unfair lock) of the ReentrantLock |
ReentrantLock class common method (Lock interfaces existing methods do not add here):
| Method name | description |
|---|---|
| int getHoldCount() | 查询当前线程保持此锁定的个数，也就是调用lock()方法的次数。 |
| protected Thread getOwner() | 返回当前拥有此锁的线程，如果不拥有，则返回 null |
| protected Collection getQueuedThreads() | 返回包含可能正在等待获取此锁的线程的集合 |
| int getQueueLength() | 返回等待获取此锁的线程数的估计。 |
| protected Collection getWaitingThreads(Condition condition) | 返回包含可能在与此锁相关联的给定条件下等待的线程的集合。 |
| int getWaitQueueLength(Condition condition) | 返回与此锁相关联的给定条件等待的线程数的估计。 |
| boolean hasQueuedThread(Thread thread) | 查询给定线程是否等待获取此锁。 |
| boolean hasQueuedThreads() | 查询是否有线程正在等待获取此锁。 |
| boolean hasWaiters(Condition condition) | 查询任何线程是否等待与此锁相关联的给定条件 |
| boolean isFair() | 如果此锁的公平设置为true，则返回 true 。 |
| boolean isHeldByCurrentThread() | 查询此锁是否由当前线程持有。 |
| boolean isLocked() | 查询此锁是否由任何线程持有。 |
2.1 第一个ReentrantLock程序
ReentrantLockTest.java
public class ReentrantLockTest {
public static void main(String[] args) {
MyService service = new MyService();
MyThread a1 = new MyThread(service);
MyThread a2 = new MyThread(service);
MyThread a3 = new MyThread(service);
MyThread a4 = new MyThread(service);
MyThread a5 = new MyThread(service);
a1.start();
a2.start();
a3.start();
a4.start();
a5.start();
}
static public class MyService {
private Lock lock = new ReentrantLock();
public void testMethod() {
lock.lock();
try {
for (int i = 0; i < 5; i++) {
System.out.println("ThreadName=" + Thread.currentThread().getName() + (" " + (i + 1)));
}
} finally {
lock.unlock();
}
}
}
static public class MyThread extends Thread {
private MyService service;
public MyThread(MyService service) {
super();
this.service = service;
}
@Override
public void run() {
service.testMethod();
}
}
}
从运行结果可以看出，当一个线程运行完毕后才把锁释放，其他线程才能执行，其他线程的执行顺序是不确定的。
2.2 Condition接口简介
一 Lock接口
1.1 Lock接口简介
锁是用于通过多个线程控制对共享资源的访问的工具。通常，锁提供对共享资源的独占访问：一次只能有一个线程可以获取锁，并且对共享资源的所有访问都要求首先获取锁。 但是，一些锁可能允许并发访问共享资源，如ReadWriteLock的读写锁。
在Lock接口出现之前，Java程序是靠synchronized关键字实现锁功能的。JDK1.5之后并发包中新增了Lock接口以及相关实现类来实现锁功能。
虽然synchronized方法和语句的范围机制使得使用监视器锁更容易编程，并且有助于避免涉及锁的许多常见编程错误，但是有时您需要以更灵活的方式处理锁。例如，用于遍历并发访问的数据结构的一些算法需要使用“手动”或“链锁定”：您获取节点A的锁定，然后获取节点B，然后释放A并获取C，然后释放B并获得D等。在这种场景中synchronized关键字就不那么容易实现了，使用Lock接口容易很多。
Lock接口的实现类：
ReentrantLock ， ReentrantReadWriteLock.ReadLock ， ReentrantReadWriteLock.WriteLock
1.2 Lock的简单使用
Lock lock=new ReentrantLock()；
lock.lock();
try{
}finally{
lock.unlock();
}
因为Lock是接口所以使用时要结合它的实现类，另外在finall语句块中释放锁的目的是保证获取到锁之后，最终能够被释放。
注意： 最好不要把获取锁的过程写在try语句块中，因为如果在获取锁时发生了异常，异常抛出的同时也会导致锁无法被释放。
1.3 Lock接口的特性和常见方法
Lock接口提供的synchronized关键字不具备的主要特性：
| 特性 | 描述 |
|---|---|
| 尝试非阻塞地获取锁 | 当前线程尝试获取锁，如果这一时刻锁没有被其他线程获取到，则成功获取并持有锁 |
| 能被中断地获取锁 | 获取到锁的线程能够响应中断，当获取到锁的线程被中断时，中断异常将会被抛出，同时锁会被释放 |
| 超时获取锁 | 在指定的截止时间之前获取锁， 超过截止时间后仍旧无法获取则返回 |
Lock接口基本的方法：
| 方法名称 | 描述 |
|---|---|
| void lock() | 获得锁。如果锁不可用，则当前线程将被禁用以进行线程调度，并处于休眠状态，直到获取锁。 |
| void lockInterruptibly() | 获取锁，如果可用并立即返回。如果锁不可用，那么当前线程将被禁用以进行线程调度，并且处于休眠状态，和lock()方法不同的是在锁的获取中可以中断当前线程（相应中断）。 |
| Condition newCondition() | 获取等待通知组件，该组件和当前的锁绑定，当前线程只有获得了锁，才能调用该组件的wait()方法，而调用后，当前线程将释放锁。 |
| boolean tryLock() | 只有在调用时才可以获得锁。如果可用，则获取锁定，并立即返回值为true；如果锁不可用，则此方法将立即返回值为false 。 |
| boolean tryLock(long time, TimeUnit unit) | 超时获取锁，当前线程在一下三种情况下会返回： 1. 当前线程在超时时间内获得了锁；2.当前线程在超时时间内被中断；3.超时时间结束，返回false. |
| void unlock() | 释放锁。 |
二 Lock接口的实现类：ReentrantLock
ReentrantLock和synchronized关键字一样可以用来实现线程之间的同步互斥，但是在功能是比synchronized关键字更强大而且更灵活。
ReentrantLock类常见方法：
构造方法：
| 方法名称 | 描述 |
|---|---|
| ReentrantLock() | 创建一个 ReentrantLock的实例。 |
| ReentrantLock(boolean fair) | 创建一个特定锁类型（公平锁/非公平锁）的ReentrantLock的实例 |
ReentrantLock类常见方法(Lock接口已有方法这里没加上)：
| 方法名称 | 描述 |
|---|---|
| int getHoldCount() | 查询当前线程保持此锁定的个数，也就是调用lock()方法的次数。 |
| protected Thread getOwner() | 返回当前拥有此锁的线程，如果不拥有，则返回 null |
| protected Collection getQueuedThreads() | 返回包含可能正在等待获取此锁的线程的集合 |
| int getQueueLength() | 返回等待获取此锁的线程数的估计。 |
| protected Collection getWaitingThreads(Condition condition) | 返回包含可能在与此锁相关联的给定条件下等待的线程的集合。 |
| int getWaitQueueLength(Condition condition) | 返回与此锁相关联的给定条件等待的线程数的估计。 |
| boolean hasQueuedThread(Thread thread) | 查询给定线程是否等待获取此锁。 |
| boolean hasQueuedThreads() | 查询是否有线程正在等待获取此锁。 |
| boolean hasWaiters(Condition condition) | 查询任何线程是否等待与此锁相关联的给定条件 |
| boolean isFair() | 如果此锁的公平设置为true，则返回 true 。 |
| boolean isHeldByCurrentThread() | 查询此锁是否由当前线程持有。 |
| boolean isLocked() | 查询此锁是否由任何线程持有。 |
2.1 第一个ReentrantLock程序
ReentrantLockTest.java
public class ReentrantLockTest {
public static void main(String[] args) {
MyService service = new MyService();
MyThread a1 = new MyThread(service);
MyThread a2 = new MyThread(service);
MyThread a3 = new MyThread(service);
MyThread a4 = new MyThread(service);
MyThread a5 = new MyThread(service);
a1.start();
a2.start();
a3.start();
a4.start();
a5.start();
}
static public class MyService {
private Lock lock = new ReentrantLock();
public void testMethod() {
lock.lock();
try {
for (int i = 0; i < 5; i++) {
System.out.println("ThreadName=" + Thread.currentThread().getName() + (" " + (i + 1)));
}
} finally {
lock.unlock();
}
}
}
static public class MyThread extends Thread {
private MyService service;
public MyThread(MyService service) {
super();
this.service = service;
}
@Override
public void run() {
service.testMethod();
}
}
}
从运行结果可以看出，当一个线程运行完毕后才把锁释放，其他线程才能执行，其他线程的执行顺序是不确定的。
2.2 Condition接口简介
我们通过之前的学习知道了：**synchronized关键字与wait()和notify/notifyAll()方法相结合可以实现等待/通知机制，ReentrantLock类当然也可以实现，但是需要借助于Condition接口与newCondition() 方法。**Condition是JDK1.5之后才有的，它具有很好的灵活性，比如可以实现多路通知功能也就是在一个Lock对象中可以创建多个Condition实例（即对象监视器），线程对象可以注册在指定的Condition中，从而可以有选择性的进行线程通知，在调度线程上更加灵活。
在使用notify/notifyAll()方法进行通知时，被通知的线程是有JVM选择的，使用ReentrantLock类结合Condition实例可以实现“选择性通知”，这个功能非常重要，而且是Condition接口默认提供的。
而synchronized关键字就相当于整个Lock对象中只有一个Condition实例，所有的线程都注册在它一个身上。如果执行notifyAll()方法的话就会通知所有处于等待状态的线程这样会造成很大的效率问题，而Condition实例的signalAll()方法 只会唤醒注册在该Condition实例中的所有等待线程
Condition接口的常见方法：
| 方法名称 | 描述 |
|---|---|
| void await() | 相当于Object类的wait方法 |
| boolean await(long time, TimeUnit unit) | 相当于Object类的wait(long timeout)方法 |
| signal() | 相当于Object类的notify方法 |
| signalAll() | 相当于Object类的notifyAll方法 |
2.3 使用Condition实现等待/通知机制
1. 使用单个Condition实例实现等待/通知机制：
UseSingleConditionWaitNotify.java
public class UseSingleConditionWaitNotify {
public static void main(String[] args) throws InterruptedException {
MyService service = new MyService();
ThreadA a = new ThreadA(service);
a.start();
Thread.sleep(3000);
service.signal();
}
static public class MyService {
private Lock lock = new ReentrantLock();
public Condition condition = lock.newCondition();
public void await() {
lock.lock();
try {
System.out.println(" await时间为" + System.currentTimeMillis());
condition.await();
System.out.println("这是condition.await()方法之后的语句，condition.signal()方法之后我才被执行");
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void signal() throws InterruptedException {
lock.lock();
try {
System.out.println("signal时间为" + System.currentTimeMillis());
condition.signal();
Thread.sleep(3000);
System.out.println("这是condition.signal()方法之后的语句");
} finally {
lock.unlock();
}
}
}
static public class ThreadA extends Thread {
private MyService service;
public ThreadA(MyService service) {
super();
this.service = service;
}
@Override
public void run() {
service.await();
}
}
}
在使用wait/notify实现等待通知机制的时候我们知道必须执行完notify()方法所在的synchronized代码块后才释放锁。在这里也差不多，必须执行完signal所在的try语句块之后才释放锁，condition.await()后的语句才能被执行。
注意： 必须在condition.await()方法调用之前调用lock.lock()代码获得同步监视器，不然会报错。
2. 使用多个Condition实例实现等待/通知机制：
UseMoreConditionWaitNotify.java
public class UseMoreConditionWaitNotify {
public static void main(String[] args) throws InterruptedException {
MyserviceMoreCondition service = new MyserviceMoreCondition();
ThreadA a = new ThreadA(service);
a.setName("A");
a.start();
ThreadB b = new ThreadB(service);
b.setName("B");
b.start();
Thread.sleep(3000);
service.signalAll_A();
}
static public class ThreadA extends Thread {
private MyserviceMoreCondition service;
public ThreadA(MyserviceMoreCondition service) {
super();
this.service = service;
}
@Override
public void run() {
service.awaitA();
}
}
static public class ThreadB extends Thread {
private MyserviceMoreCondition service;
public ThreadB(MyserviceMoreCondition service) {
super();
this.service = service;
}
@Override
public void run() {
service.awaitB();
}
}
}
MyserviceMoreCondition.java
public class MyserviceMoreCondition {
private Lock lock = new ReentrantLock();
public Condition conditionA = lock.newCondition();
public Condition conditionB = lock.newCondition();
public void awaitA() {
lock.lock();
try {
System.out.println("begin awaitA时间为" + System.currentTimeMillis()
+ " ThreadName=" + Thread.currentThread().getName());
conditionA.await();
System.out.println(" end awaitA时间为" + System.currentTimeMillis()
+ " ThreadName=" + Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void awaitB() {
lock.lock();
try {
System.out.println("begin awaitB时间为" + System.currentTimeMillis()
+ " ThreadName=" + Thread.currentThread().getName());
conditionB.await();
System.out.println(" end awaitB时间为" + System.currentTimeMillis()
+ " ThreadName=" + Thread.currentThread().getName());
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void signalAll_A() {
lock.lock();
try {
System.out.println(" signalAll_A时间为" + System.currentTimeMillis()
+ " ThreadName=" + Thread.currentThread().getName());
conditionA.signalAll();
} finally {
lock.unlock();
}
}
public void signalAll_B() {
lock.lock();
try {
System.out.println(" signalAll_B时间为" + System.currentTimeMillis()
+ " ThreadName=" + Thread.currentThread().getName());
conditionB.signalAll();
} finally {
lock.unlock();
}
}
}
只有A线程被唤醒了。
3. 使用Condition实现顺序执行
ConditionSeqExec.java
public class ConditionSeqExec {
volatile private static int nextPrintWho = 1;
private static ReentrantLock lock = new ReentrantLock();
final private static Condition conditionA = lock.newCondition();
final private static Condition conditionB = lock.newCondition();
final private static Condition conditionC = lock.newCondition();
public static void main(String[] args) {
Thread threadA = new Thread() {
public void run() {
try {
lock.lock();
while (nextPrintWho != 1) {
conditionA.await();
}
for (int i = 0; i < 3; i++) {
System.out.println("ThreadA " + (i + 1));
}
nextPrintWho = 2;
//通知conditionB实例的线程运行
conditionB.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
};
Thread threadB = new Thread() {
public void run() {
try {
lock.lock();
while (nextPrintWho != 2) {
conditionB.await();
}
for (int i = 0; i < 3; i++) {
System.out.println("ThreadB " + (i + 1));
}
nextPrintWho = 3;
//通知conditionC实例的线程运行
conditionC.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
};
Thread threadC = new Thread() {
public void run() {
try {
lock.lock();
while (nextPrintWho != 3) {
conditionC.await();
}
for (int i = 0; i < 3; i++) {
System.out.println("ThreadC " + (i + 1));
}
nextPrintWho = 1;
//通知conditionA实例的线程运行
conditionA.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
};
Thread[] aArray = new Thread[5];
Thread[] bArray = new Thread[5];
Thread[] cArray = new Thread[5];
for (int i = 0; i < 5; i++) {
aArray[i] = new Thread(threadA);
bArray[i] = new Thread(threadB);
cArray[i] = new Thread(threadC);
aArray[i].start();
bArray[i].start();
cArray[i].start();
}
}
}
Condition实现顺序执行运行结果
通过代码很好理解，说简单就是在一个线程运行完之后通过condition.signal()/condition.signalAll()方法通知下一个特定的运行运行，就这样循环往复即可。
注意： 默认情况下ReentranLock类使用的是非公平锁
2.4 公平锁与非公平锁
Lock锁分为：公平锁 和 非公平锁。公平锁表示线程获取锁的顺序是按照线程加锁的顺序来分配的，即先来先得的FIFO先进先出顺序。而非公平锁就是一种获取锁的抢占机制，是随机获取锁的，和公平锁不一样的就是先来的不一定先的到锁，这样可能造成某些线程一直拿不到锁，结果也就是不公平的了。
FairorNofairLock.java
public class FairorNofairLock {
public static void main(String[] args) throws InterruptedException {
final Service service = new Service(true);//true为公平锁，false为非公平锁
Runnable runnable = new Runnable() {
@Override
public void run() {
System.out.println("★线程" + Thread.currentThread().getName()
+ "运行了");
service.serviceMethod();
}
};
Thread[] threadArray = new Thread[10];
for (int i = 0; i < 10; i++) {
threadArray[i] = new Thread(runnable);
}
for (int i = 0; i < 10; i++) {
threadArray[i].start();
}
}
static public class Service {
private ReentrantLock lock;
public Service(boolean isFair) {
super();
lock = new ReentrantLock(isFair);
}
public void serviceMethod() {
lock.lock();
try {
System.out.println("ThreadName=" + Thread.currentThread().getName()
+ "获得锁定");
} finally {
lock.unlock();
}
}
}
}
公平锁的运行结果是有序的。
把Service的参数修改为false则为非公平锁
final Service service = new Service(false);//true为公平锁，false为非公平锁
非公平锁的运行结果是无序的。
三 ReadWriteLock接口的实现类：ReentrantReadWriteLock
3.1 简介
我们刚刚接触到的ReentrantLock（排他锁）具有完全互斥排他的效果，即同一时刻只允许一个线程访问，这样做虽然虽然保证了实例变量的线程安全性，但效率非常低下。ReadWriteLock接口的实现类-ReentrantReadWriteLock读写锁就是为了解决这个问题。
读写锁维护了两个锁，一个是读操作相关的锁也成为共享锁，一个是写操作相关的锁 也称为排他锁。通过分离读锁和写锁，其并发性比一般排他锁有了很大提升。
**多个读锁之间不互斥，读锁与写锁互斥，写锁与写锁互斥（只要出现写操作的过程就是互斥的。）。**在没有线程Thread进行写入操作时，进行读取操作的多个Thread都可以获取读锁，而进行写入操作的Thread只有在获取写锁后才能进行写入操作。即多个Thread可以同时进行读取操作，但是同一时刻只允许一个Thread进行写入操作。
**
3.2 ReentrantReadWriteLock的特性与常见方法
**
ReentrantReadWriteLock的特性：
| 特性 | 说明 |
|---|---|
| 公平性选择 | 支持非公平（默认）和公平的锁获取方式，吞吐量上来看还是非公平优于公平 |
| 重进入 | 该锁支持重进入，以读写线程为例：读线程在获取了读锁之后，能够再次获取读锁。而写线程在获取了写锁之后能够再次获取写锁也能够同时获取读锁 |
| 锁降级 | 遵循获取写锁、获取读锁再释放写锁的次序，写锁能够降级称为读锁 |
ReentrantReadWriteLock常见方法：
| 方法名称 | 描述 |
|---|---|
| ReentrantReadWriteLock() | 创建一个 ReentrantReadWriteLock()的实例 |
| ReentrantReadWriteLock(boolean fair) | Create an instance of a particular type of lock (lock fair / unfair lock) of the ReentrantReadWriteLock |
Use of 3.3 ReentrantReadWriteLock
- Read Share
Two threads to run simultaneously read method, you will find two threads can run simultaneously or almost simultaneously lock () the same time two sentences back method code, the output is displayed. This increases the efficiency of the program.
private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
public void read() {
try {
try {
lock.readLock().lock();
System.out.println("获得读锁" + Thread.currentThread().getName()
+ " " + System.currentTimeMillis());
Thread.sleep(10000);
} finally {
lock.readLock().unlock();
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
- Exclusive write
the above code
lock.readLock().lock();
Read:
lock.writeLock().lock();
Two threads to run simultaneously read method, you'll find the same time allowing only one execution thread lock () method code behind
- Reading and writing are mutually exclusive
private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
public void read() {
try {
try {
lock.readLock().lock();
System.out.println("获得读锁" + Thread.currentThread().getName()
+ " " + System.currentTimeMillis());
Thread.sleep(10000);
} finally {
lock.readLock().unlock();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public void write() {
try {
try {
lock.writeLock().lock();
System.out.println("获得写锁" + Thread.currentThread().getName()
+ " " + System.currentTimeMillis());
Thread.sleep(10000);
} finally {
lock.writeLock().unlock();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
Test code:
Service service = new Service();
ThreadA a = new ThreadA(service);
a.setName("A");
a.start();
Thread.sleep(1000);
ThreadB b = new ThreadB(service);
b.setName("B");
b.start();
Service two runs using the same object instance threads a, b, a thread performs read the above method, the thread b perform the above write method. You will find the same time allowing only one execution thread lock () method code behind. Remember: as long as the process of the emergence of a write operation is mutually exclusive.
- Read exclusive write
And read-write mutually exclusive Similarly, no code demonstrates here. Remember: as long as the process of the emergence of a write operation is mutually exclusive.
Address reprint: https://blog.csdn.net/qq_34337272/article/details/79714196