The difference between synchronized and reentrantlock

Catalog

juc Common subclasses under

1. Object lock juc.lock

2. synchronized and ReentrantLock The difference between

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juc Common subclasses under

1. Object lock juc.lock

Object lock juc.lock ——JDK1.0 There is , need JVM With the help of the operating system mutex System statement implementation .

JDK1.5 after ,Java The implementation of mutual exclusion implemented by the language itself , Without the help of the operating system monitor Mechanism .
stay Java In addition to synchronized Keywords can be implemented outside the object lock ,java.util.concurrent Medium Lock Interface You can also implement object locks .

Use Lock The interface needs to be displayed for locking and unlocking

And synchronized The difference is , There is one tryLock Method

Lock , The thread that failed to acquire the lock enters the blocking state , Wait for a while , After the time has passed, if the lock has not been obtained, resume execution , Give up locking , Execute other code

Unlock operation

Code demonstration

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.ReentrantLock;

public class LockTest {
    public static void main(String[] args) {
        ReentrantLock lock = new ReentrantLock();
        Thread t1 = new Thread(() -> {
            lock.lock(); //  The code locks from here , Until I met unlock Unlock 
            //  Mutually exclusive code block 
            try {
                System.out.println(Thread.currentThread().getName() + " Get lock , Other threads wait ");
                Thread.sleep(8000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } finally {
                //  Only the thread that successfully obtains the lock needs to execute unlock Method 
                lock.unlock();
            }
            System.out.println(Thread.currentThread().getName() + " Release the lock ");
        }, "1 Number ");
        t1.start();
        Thread t2 = new Thread(() -> {
            boolean isLock = false;
            try {
                isLock = lock.tryLock(3000, TimeUnit.MICROSECONDS);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } finally {
                if (isLock) {
                    //  Only the thread that successfully obtains the lock needs to execute unlock Method 
                    lock.unlock();
                }
            }
            System.out.println(" Wait only 3 second ");
        }, "2 Number ");
        t2.start();
    }
}

2. synchronized and ReentrantLock The difference between

1. synchronized yes Java Key words of , from JVM Realization , You need to rely on what the operating system provides Thread mutex primitive (mutex);

Lock Classes and interfaces of the standard library , One of the most commonly used subclasses (ReentrantLock, Reentrant lock ), from Java It is realized by itself , There is no need to rely on the operating system .

2. synchronized Implicit Lock and unlock ,lock need Display progress Lock and unlock .

3. synchronized When the thread that failed to acquire the lock , Death etc. ;

lock have access to tryLock Wait for a period of time and then give up automatically Lock , The thread resumes execution .

4. synchronized Fair lock ;

ReentrantLock Default is unfair lock , In the construction method Pass in true Open the fair lock .

5. synchronized Read / write locks are not supported ,Lock Subclass ReentrantReadWriteLock Read and write lock support .

General scene synchronized Enough , You need to wait for the lock with timeout , Fair lock , Consider using read-write lock juc.lock.