synchronized和reentrantlock到底锁了什么？
第一个类，在add clear等方法里使用可重入锁 java
public class LockList extends ArrayList<Object>{
private Lock lock = new ReentrantLock(false);
@Override
public boolean add(Object o) {
lock.lock();
try{
System.out.println(Thread.currentThread().getName()+"add lock");
return super.add(o);
}finally {
System.out.println(Thread.currentThread().getName()+"add unlock");
lock.unlock();
}
}
@Override
public void clear() {
lock.lock();
try{
System.out.println(Thread.currentThread().getName()+"clear lock");
super.clear();
}finally {
System.out.println(Thread.currentThread().getName()+"clear unlock");
lock.unlock();
}
}
@Override
public int size() {
lock.lock();
try{
System.out.println(Thread.currentThread().getName()+"clear lock");
return super.size();
}finally {
System.out.println(Thread.currentThread().getName()+"clear unlock");
lock.unlock();
}
}
public static void main(String[] args) {
final LockList list = new LockList();
for(int i=0;i<110;i++){
final int j = i;
new Thread(){
@Override
public void run() {
setName("线程"+j);
list.add(j);
list.clear();
}
}.start();
}
}
}
第二个类，在add remove方法里使用synchronized关键字编程
public class SyncList extends ArrayList<Object> {
@Override
public boolean add(Object o) {
synchronized (this){
System.out.println(Thread.currentThread().getName() +"add synchronized lock");
boolean r= super.add(o);
System.out.println(Thread.currentThread().getName() +"add synchronized unlock");
return r;
}
}
@Override
public void clear() {
synchronized (this){
System.out.println(Thread.currentThread().getName() +"clear synchronized lock");
super.clear();
System.out.println(Thread.currentThread().getName() +"clear synchronized unlock");
}
}
@Override
public int size() {
synchronized (this){
System.out.println(Thread.currentThread().getName() +"size synchronized lock");
int r= super.size();
System.out.println(Thread.currentThread().getName() +"size synchronized unlock");
return r;
}
}
@Override
public boolean addAll(Collection<?> c) {
synchronized (this) {
System.out.println(Thread.currentThread().getName() +"addAll synchronized lock");
boolean r= super.addAll(c);
System.out.println(Thread.currentThread().getName() +"addAll synchronized unlock");
return r;
}
}
@Override
public boolean remove(Object o) {
synchronized (this){
System.out.println(Thread.currentThread().getName() +"remove synchronized lock");
boolean r= super.remove(o);
System.out.println(Thread.currentThread().getName() +"remove synchronized unlock");
return r;
}
}
public static void main(String[] args) {
final SyncList list = new SyncList();
for(int i=0;i<110;i++){
final int j = i;
new Thread(){
@Override
public void run() {
setName("线程"+j);
// list.add(j);
list.remove(new Integer(j));
}
}.start();
}
}
}
第一个结果，能够看到lock和unlock都是成在一个同一个线程里对出现的，说明了调用该方法时另外的线程是进不来的，或者说进入等待队列，这个要看AbstractQueueSynchronized的源码，他对锁进行了优化。并发
线程2add lock 线程2add unlock 线程2clear lock 线程2clear unlock 线程3add lock 线程3add unlock 线程3clear lock 线程3clear unlock 线程5add lock 线程5add unlock 线程5clear lock 线程5clear unlock 线程8add lock 线程8add unlock 线程8clear lock 线程8clear unlock 线程15add lock 线程15add unlock 线程23add lock 线程23add unlock 线程23clear lock 线程23clear unlock 线程15clear lock 线程15clear unlock 线程26add lock 线程26add unlock 线程26clear lock 线程26clear unlock 线程20add lock 线程20add unlock 线程20clear lock 线程20clear unlock 线程32add lock 线程32add unlock 线程32clear lock 线程32clear unlock 线程9add lock 线程9add unlock 线程9clear lock 线程9clear unlock 线程35add lock 线程35add unlock 线程35clear lock 线程35clear unlock 线程14add lock 线程14add unlock 线程14clear lock 线程14clear unlock 线程45add lock 线程45add unlock 线程45clear lock 线程45clear unlock 线程21add lock 线程21add unlock 线程21clear lock 线程21clear unlock 线程27add lock 线程27add unlock 线程27clear lock 线程27clear unlock 线程62add lock 线程62add unlock 线程68add lock 线程68add unlock 线程68clear lock 线程68clear unlock 线程1add lock 线程1add unlock 线程1clear lock 线程1clear unlock 线程33add lock 线程33add unlock 线程33clear lock 线程33clear unlock 线程6add lock 线程6add unlock 线程39add lock 线程39add unlock 线程39clear lock 线程39clear unlock 线程18add lock 线程18add unlock 线程18clear lock 线程18clear unlock 线程44add lock 线程44add unlock 线程44clear lock 线程44clear unlock 线程24add lock 线程24add unlock 线程30add lock 线程30add unlock 线程30clear lock 线程30clear unlock 线程63add lock 线程63add unlock 线程63clear lock 线程63clear unlock 线程41add lock 线程41add unlock 线程41clear lock 线程41clear unlock 线程17add lock 线程17add unlock 线程17clear lock 线程17clear unlock 线程105add lock 线程105add unlock 线程105clear lock 线程105clear unlock 线程99add lock 线程99add unlock 线程99clear lock 线程99clear unlock 线程92add lock 线程92add unlock 线程87add lock 线程87add unlock 线程87clear lock 线程87clear unlock 线程109add lock 线程109add unlock 线程109clear lock 线程109clear unlock 线程96add lock 线程96add unlock 线程96clear lock 线程96clear unlock 线程79add lock 线程79add unlock 线程79clear lock 线程79clear unlock 线程72add lock 线程72add unlock 线程72clear lock 线程72clear unlock 线程47add lock 线程47add unlock 线程47clear lock 线程47clear unlock 线程50add lock 线程50add unlock 线程50clear lock 线程50clear unlock 线程53add lock 线程53add unlock 线程53clear lock 线程53clear unlock 线程51add lock 线程51add unlock 线程51clear lock 线程51clear unlock 线程56add lock 线程56add unlock 线程56clear lock 线程56clear unlock 线程59add lock 线程59add unlock 线程59clear lock 线程59clear unlock 线程65add lock 线程65add unlock 线程65clear lock 线程65clear unlock 线程62clear lock 线程62clear unlock 线程69add lock 线程69add unlock 线程69clear lock 线程69clear unlock 线程0add lock 线程0add unlock 线程0clear lock 线程0clear unlock 线程4add lock 线程4add unlock 线程4clear lock 线程4clear unlock 线程7add lock 线程7add unlock 线程7clear lock 线程7clear unlock 线程10add lock 线程10add unlock 线程10clear lock 线程10clear unlock 线程12add lock 线程12add unlock 线程12clear lock 线程12clear unlock 线程6clear lock 线程6clear unlock 线程16add lock 线程16add unlock 线程16clear lock 线程16clear unlock 线程19add lock 线程19add unlock 线程19clear lock 线程19clear unlock 线程22add lock 线程22add unlock 线程22clear lock 线程22clear unlock 线程28add lock 线程28add unlock 线程28clear lock 线程28clear unlock 线程25add lock 线程25add unlock 线程25clear lock 线程25clear unlock 线程13add lock 线程13add unlock 线程13clear lock 线程13clear unlock 线程34add lock 线程34add unlock 线程34clear lock 线程34clear unlock 线程71add lock 线程71add unlock 线程71clear lock 线程71clear unlock 线程57add lock 线程57add unlock 线程57clear lock 线程57clear unlock 线程38add lock 线程38add unlock 线程38clear lock 线程38clear unlock 线程29add lock 线程29add unlock 线程29clear lock 线程29clear unlock 线程104add lock 线程104add unlock 线程104clear lock 线程104clear unlock 线程11add lock 线程11add unlock 线程11clear lock 线程11clear unlock 线程107add lock 线程107add unlock 线程107clear lock 线程107clear unlock 线程101add lock 线程101add unlock 线程101clear lock 线程101clear unlock 线程98add lock 线程98add unlock 线程98clear lock 线程98clear unlock 线程95add lock 线程95add unlock 线程95clear lock 线程95clear unlock 线程93add lock 线程93add unlock 线程93clear lock 线程93clear unlock 线程80add lock 线程80add unlock 线程80clear lock 线程80clear unlock 线程77add lock 线程77add unlock 线程77clear lock 线程77clear unlock 线程89add lock 线程89add unlock 线程89clear lock 线程89clear unlock 线程86add lock 线程86add unlock 线程86clear lock 线程86clear unlock 线程92clear lock 线程92clear unlock 线程83add lock 线程83add unlock 线程83clear lock 线程83clear unlock 线程81add lock 线程81add unlock 线程81clear lock 线程81clear unlock 线程75add lock 线程75add unlock 线程75clear lock 线程75clear unlock 线程106add lock 线程106add unlock 线程106clear lock 线程106clear unlock 线程108add lock 线程108add unlock 线程108clear lock 线程108clear unlock 线程103add lock 线程103add unlock 线程103clear lock 线程103clear unlock 线程102add lock 线程102add unlock 线程102clear lock 线程102clear unlock 线程97add lock 线程97add unlock 线程97clear lock 线程97clear unlock 线程94add lock 线程94add unlock 线程94clear lock 线程94clear unlock 线程100add lock 线程100add unlock 线程100clear lock 线程100clear unlock 线程91add lock 线程91add unlock 线程91clear lock 线程91clear unlock 线程85add lock 线程85add unlock 线程85clear lock 线程85clear unlock 线程88add lock 线程88add unlock 线程88clear lock 线程88clear unlock 线程90add lock 线程90add unlock 线程90clear lock 线程90clear unlock 线程84add lock 线程84add unlock 线程84clear lock 线程84clear unlock 线程82add lock 线程82add unlock 线程82clear lock 线程82clear unlock 线程78add lock 线程78add unlock 线程78clear lock 线程78clear unlock 线程76add lock 线程76add unlock 线程76clear lock 线程76clear unlock 线程73add lock 线程73add unlock 线程73clear lock 线程73clear unlock 线程70add lock 线程70add unlock 线程70clear lock 线程70clear unlock 线程67add lock 线程67add unlock 线程67clear lock 线程67clear unlock 线程60add lock 线程60add unlock 线程60clear lock 线程60clear unlock 线程58add lock 线程58add unlock 线程58clear lock 线程58clear unlock 线程49add lock 线程49add unlock 线程49clear lock 线程49clear unlock 线程54add lock 线程54add unlock 线程54clear lock 线程54clear unlock 线程52add lock 线程52add unlock 线程52clear lock 线程52clear unlock 线程48add lock 线程48add unlock 线程48clear lock 线程48clear unlock 线程42add lock 线程42add unlock 线程42clear lock 线程42clear unlock 线程64add lock 线程64add unlock 线程64clear lock 线程64clear unlock 线程40add lock 线程40add unlock 线程40clear lock 线程40clear unlock 线程24clear lock 线程24clear unlock 线程31add lock 线程31add unlock 线程31clear lock 线程31clear unlock 线程46add lock 线程46add unlock 线程46clear lock 线程46clear unlock 线程66add lock 线程66add unlock 线程66clear lock 线程66clear unlock 线程36add lock 线程36add unlock 线程36clear lock 线程36clear unlock 线程61add lock 线程61add unlock 线程61clear lock 线程61clear unlock 线程43add lock 线程43add unlock 线程43clear lock 线程43clear unlock 线程74add lock 线程74add unlock 线程74clear lock 线程74clear unlock 线程37add lock 线程37add unlock 线程37clear lock 线程37clear unlock 线程55add lock 线程55add unlock 线程55clear lock 线程55clear unlock Process finished with exit code 0
第二个是你们都熟悉的synchorized关键字，打印结果只贴一部分，能够看到结果和上面同样，在加锁的操做里只有一个线程能进方法，也就是持有该对象，固然对于没有加锁的方法依然能够被多个线程同时访问（这个是老师教可是没有本身证明过）。ide
线程59clear lock 线程59clear unlock 线程60add lock 线程60add unlock 线程60clear lock 线程60clear unlock 线程55add lock 线程55add unlock 线程55clear lock 线程55clear unlock 线程56add lock 线程56add unlock 线程56clear lock 线程56clear unlock 线程51add lock 线程51add unlock 线程51clear lock 线程51clear unlock 线程43add lock 线程43add unlock 线程43clear lock 线程43clear unlock 线程48add lock 线程48add unlock 线程48clear lock 线程48clear unlock 线程72add lock 线程72add unlock 线程72clear lock 线程72clear unlock 线程63add lock 线程63add unlock 线程63clear lock 线程63clear unlock 线程77add lock 线程77add unlock 线程77clear lock 线程77clear unlock 线程14add lock 线程14add unlock 线程14clear lock 线程14clear unlock 线程76add lock 线程76add unlock 线程76clear lock 线程76clear unlock 线程64add lock 线程64add unlock 线程64clear lock 线程64clear unlock 线程49add lock 线程49add unlock 线程49clear lock 线程49clear unlock 线程61add lock 线程61add unlock 线程61clear lock 线程61clear unlock 线程57add lock 线程57add unlock 线程57clear lock 线程57clear unlock 线程18add lock 线程18add unlock 线程18clear lock 线程18clear unlock 线程54add lock 线程54add unlock 线程54clear lock 线程54clear unlock
因此结论是可重入锁锁的是当前持有锁的对象对象，和synchronized关键字锁的后面括号里的对象，能够看出sync关键字的可读性更好，由于能够直接看到后面括号里的类或对象，而可重入锁没有。可是可重入锁的性能更好（具体好多少后面再出个博文），sync是系统级别函数调用开销大（这句话是并发编程的艺术这本书里写的，背下来）函数
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