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Explication détaillée de l'utilisation de synchronisé pour implémenter un code de verrouillage
- php中世界最好的语言original
- 2017-12-20 11:56:032479parcourir
Cet article présente comment utiliser synchronisé pour implémenter un code de verrouillage. Ce qui suit est un cas pratique. Les amis dans le besoin peuvent s'y référer.
Méthode 1 :
public synchronized void a(){
//TODO
}Méthode 2 :
public void b(){
synchronized(this){
//TODO
}
}D'ici Dans les deux cas, le verrou est ajouté entre ｛｝. Voyons comment le verrouillage est effectué :
public void c() {
lock.lock();
try {
// TODO
} finally {
lock.unlock();
}
}De cette façon, le verrou est ajouté entre lock(). et unlock(), donc si vous souhaitez implémenter une fonction de verrouillage, vous devez réfléchir à la façon d'implémenter ces deux méthodes, les méthodes lock() et unlock(). Définissez d'abord un frameworkComme indiqué ci-dessous :
public void lock(){
}
public void unlock(){
}
Ensuite, vous souhaitez utiliser synchronisé pour implémenter ces deux méthodes.
Maintenant, j'ai en fait une idée un peu plus claire, mais je ne sais toujours pas comment remplir ces deux méthodes. J'analyserai les caractéristiques de Lock plus tard et jetterai un œil à ce code :
public void c() {
lock.lock();
//When current thread get the lock, other thread has to wait
try {
//current thread get in the lock, other thread can not get in
// TODO
}
finally {
lock.unlock();
//current thread release the lock
}
}
Je viens d'ajouter un petit commentaire à ce code et je n'ai rien fait d'autre. Cela aide-t-il à comprendre ce code ? mot fréquent ? Il s'agit de currentthread. Alors, lorsque nous remplissons les méthodes lock() et unlock(), devons-nous faire attention au mot-clé currentthread pour trouver la solution ? La réponse est oui.
Ensuite, analysez, comment faire attendre le fil lors d'une utilisation synchronisée ? Utilisez la méthode wait(). Comment réveiller le thread ? Utilisez la méthode notify(). Utilisez ensuite la méthode wait() dans la méthode lock() et la méthode notify() dans la méthode unlock(). Il y a donc une condition lorsque nous utilisons wait() et notify(). Pensez à ce que nous devrions utiliser comme condition ?
Nous devrions utiliser si le verrou actuel est occupé comme condition de jugement. Si le verrou est occupé, currentthread attend. Demandez-vous si nous avons toujours utilisé cette condition lors de l'utilisation de synchronisé, la réponse est oui.
Analysons quand libérer le verrou et quelles conditions sont utilisées. Pensez-y. Si le thread A obtient le verrou, le thread B peut-il le libérer ? Bien sûr que non. Si B pouvait être libéré, cela violerait le principe. Il faut que le verrou du thread A ne puisse être libéré que par le thread A. La condition de jugement est donc de juger si le thread qui détient le verrou est le thread actuel. Si c'est le cas, il peut être libéré. Sinon, bien sûr, il ne peut pas.
Jetons maintenant un œil au code complet :
package test.lock;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
public class NaiveLock {
private static final long NONE = -1;
private long owner = NONE;
private Boolean isLooked() {
return owner != NONE;
}
public synchronized void lock() {
long currentThreadId = Thread.currentThread().getId();
if (owner == currentThreadId) {
throw new IllegalStateException("Lock has been acquired by current thread");
}
while (this.isLooked()) {
System.out.println(String.format("thread %s is waitting lock", currentThreadId));
try {
wait();
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
owner = currentThreadId;
System.out.println(String.format("Lock is acquired by thread %s", owner));
}
public synchronized void unlock() {
if (!this.isLooked() || owner != Thread.currentThread().getId()) {
throw new IllegalStateException("Only Lock owner can unlock the lock");
}
System.out.println(String.format("thread %s is unlocking", owner));
System.out.println();
owner = NONE;
notify();
}
public static void main(String[] args) {
final NaiveLock lock = new NaiveLock();
ExecutorService executor = Executors.newFixedThreadPool(20, new ThreadFactory() {
private ThreadGroup group = new ThreadGroup("test thread group");
{
group.setDaemon(true);
}
@Override
public Thread newThread(Runnable r) {
return new Thread(group, r);
}
}
);
for (int i = 0; i < 20; i++) {
executor.submit(new Runnable() {
@Override
public void run() {
lock.lock();
System.out.println(String.format("thread %s is running...", Thread.currentThread().getId()));
try {
Thread.sleep(new Random().nextint(1000));
}
catch (InterruptedException e) {
e.printStackTrace();
}
lock.unlock();
}
}
);
}
}
}
Exécutez-le et voyez le résultat :
Lock is acquired by thread 8 thread 8 is running... thread 27 is waitting lock thread 26 is waitting lock thread 25 is waitting lock thread 24 is waitting lock thread 23 is waitting lock thread 22 is waitting lock thread 21 is waitting lock thread 20 is waitting lock thread 19 is waitting lock thread 18 is waitting lock thread 17 is waitting lock thread 16 is waitting lock thread 15 is waitting lock thread 14 is waitting lock thread 13 is waitting lock thread 12 is waitting lock thread 11 is waitting lock thread 10 is waitting lock thread 9 is waitting lock thread 8 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 27 is unlocking Lock is acquired by thread 26 thread 26 is running... thread 26 is unlocking Lock is acquired by thread 25 thread 25 is running... thread 25 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 23 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 22 is unlocking Lock is acquired by thread 21 thread 21 is running... thread 21 is unlocking Lock is acquired by thread 20 thread 20 is running... thread 20 is unlocking Lock is acquired by thread 19 thread 19 is running... thread 19 is unlocking Lock is acquired by thread 18 thread 18 is running... thread 18 is unlocking Lock is acquired by thread 17 thread 17 is running... thread 17 is unlocking Lock is acquired by thread 16 thread 16 is running... thread 16 is unlocking Lock is acquired by thread 15 thread 15 is running... thread 15 is unlocking Lock is acquired by thread 14 thread 14 is running... thread 14 is unlocking Lock is acquired by thread 13 thread 13 is running... thread 13 is unlocking Lock is acquired by thread 12 thread 12 is running... thread 12 is unlocking Lock is acquired by thread 11 thread 11 is running... thread 11 is unlocking Lock is acquired by thread 10 thread 10 is running... thread 10 is unlocking Lock is acquired by thread 9 thread 9 is running... thread 9 is unlocking
Si vous modifiez la boucle for à 30 fois, regardez à nouveau le résultat :
Lock is acquired by thread 8 thread 8 is running... thread 27 is waitting lock thread 26 is waitting lock thread 25 is waitting lock thread 24 is waitting lock thread 23 is waitting lock thread 22 is waitting lock thread 21 is waitting lock thread 20 is waitting lock thread 19 is waitting lock thread 18 is waitting lock thread 17 is waitting lock thread 16 is waitting lock thread 15 is waitting lock thread 14 is waitting lock thread 13 is waitting lock thread 12 is waitting lock thread 11 is waitting lock thread 10 is waitting lock thread 9 is waitting lock thread 8 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 8 is waitting lock thread 27 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 26 is waitting lock thread 27 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 25 is waitting lock thread 27 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 27 is waitting lock thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 24 is waitting lock thread 23 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 23 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 21 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 20 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 19 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 18 is waitting lock thread 22 is unlocking Lock is acquired by thread 17 thread 17 is running... thread 17 is unlocking Lock is acquired by thread 16 thread 16 is running... thread 16 is unlocking Lock is acquired by thread 15 thread 15 is running... thread 15 is unlocking Lock is acquired by thread 14 thread 14 is running... thread 14 is unlocking Lock is acquired by thread 13 thread 13 is running... thread 13 is unlocking Lock is acquired by thread 12 thread 12 is running... thread 12 is unlocking Lock is acquired by thread 11 thread 11 is running... thread 11 is unlocking Lock is acquired by thread 10 thread 10 is running... thread 10 is unlocking Lock is acquired by thread 9 thread 9 is running... thread 9 is unlocking Lock is acquired by thread 8 thread 8 is running... thread 8 is unlocking Lock is acquired by thread 26 thread 26 is running... thread 26 is unlocking Lock is acquired by thread 25 thread 25 is running... thread 25 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 27 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 23 is unlocking Lock is acquired by thread 21 thread 21 is running... thread 21 is unlocking Lock is acquired by thread 20 thread 20 is running... thread 20 is unlocking Lock is acquired by thread 19 thread 19 is running... thread 19 is unlocking Lock is acquired by thread 18 thread 18 is running... thread 18 is unlocking
Je pense que vous maîtrisez les méthodes après avoir lu ces cas. Pour des informations plus intéressantes, veuillez prêter attention aux autres articles connexes sur le site Web chinois de php !
Lecture connexe :
Le tutoriel d'algorithme de correspondance de chaînes le plus simple en php
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