Condition的功能類似在傳統線程技術中的Object.wait和Object.notify的功能。在等待Condition時,允許發生“虛假喚醒”,這通常作爲對基礎平臺語義的讓步。對於大多數應用程序,這帶來的實際影響很小,因爲Condition應該總是在一個循環中被等待,並測試正被等待的狀態聲明。某個實現可以隨意移除可能的虛假喚醒,但建議應用程序員總是假定這些虛假喚醒可能發生,因此總是在一個循環中等待。
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 題目:子線程循環10次,接着主線程循環100,接着又回到子線程循環10次,主線程循環100次,
* 如此循環50次
*
*/
publicclass ConditionCommunicate {
publicstaticvoid main(String[] args) {
Business business = new Business();
new Thread(new Runnable(){
@Override
publicvoid run() {
for(inti= 0 ; i< 50 ; i++){
business.sub(i);
}
}
}).start();
for(inti= 0 ; i< 50 ; i++){
business.main(i);
}
}
publicvoid init(){
}
/**
* 這個類是內部類,但用static修飾相當於外部類,他的名稱是:ConditionCommunicate.Business
*/
staticclass Business{
Lock lock = new ReentrantLock();
Condition condition = lock.newCondition();
privatebooleanbShouldSub = true;
publicvoid sub(inti){
lock.lock();
try{
while(!bShouldSub){
try {
condition.await();//使用condition替換原來的wait
// this.wait(); //wait和notify必須在synchronized內部使用
} catch (Exception e) {
e.printStackTrace();
}
}
for(intj = 0 ; j< 10; j++){
System.out.println("sub Thread cycle of "+ j +", loop of "+ i);
}
bShouldSub = false;
condition.signal();//使用condition替換原來的notify
// this.notify();
}finally{
lock.unlock();
}
}
publicvoid main(inti){
lock.lock();
try{
//這裏while要比if好,會防止僞喚醒。
while(bShouldSub){
try {
// this.wait();
condition.await();
} catch (Exception e) {
e.printStackTrace();
}
}
for(intj = 0 ; j< 5; j++){
System.out.println("main Thread cycle of "+ j +", loop of "+ i);
}
bShouldSub = true;
// this.notify();
condition.signal();
}finally{
lock.unlock();
}
}
}
}
用到多個Condition
put
和 take
方法。如果試圖在空的緩衝區上執行 take
操作,則在某一個項變得可用之前,線程將一直阻塞;如果試圖在滿的緩衝區上執行 put
操作,則在有空間變得可用之前,線程將一直阻塞。我們喜歡在單獨的等待
set 中保存 put
線程和 take
線程,這樣就可以在緩衝區中的項或空間變得可用時利用最佳規劃,一次只通知一個線程。可以使用兩個 Condition
實例來做到這一點。class BoundedBuffer {
final Lock lock = new ReentrantLock();
final Condition notFull = lock.newCondition();
final Condition notEmpty = lock.newCondition();
final Object[] items = new Object[100];
intputptr, takeptr, count;
publicvoid put(Object x) throws InterruptedException {
lock.lock();
try {
while (count == items.length)
notFull.await();
items[putptr] = x;
if (++putptr == items.length) putptr = 0;
++count;
notEmpty.signal();
} finally {
lock.unlock();
}
}
public Object take() throws InterruptedException {
lock.lock();
try {
while (count == 0)
notEmpty.await();
Object x = items[takeptr];
if (++takeptr == items.length) takeptr = 0;
--count;
notFull.signal();
returnx;
} finally {
lock.unlock();
}
}
}
三個線程循環走(用到三個Condition):
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* 題目:子線程循環10次,接着主線程循環100,接着又回到子線程循環10次,主線程循環100次,
* 如此循環50次
* 在此題目上改進,有三個線程,老大先走,老大走完老二走,老二走完老三走。這樣循環
* 這樣就要用到多個Condition條件
* 老大喚醒老二需要condition、老二喚醒老三需要condition、老三喚醒老大需要condition。所以需要
* 三個condition
*/
publicclass ThreeConditionCommunicate {
publicstaticvoid main(String[] args) {
Business business = new Business();
new Thread(new Runnable(){
@Override
publicvoid run() {
for(inti= 0 ; i< 50 ; i++){
business.sub2(i);
}
}
}).start();
new Thread(new Runnable(){
@Override
publicvoid run() {
for(inti= 0 ; i< 50 ; i++){
business.sub3(i);
}
}
}).start();
for(inti= 0 ; i< 50 ; i++){
business.main(i);
}
}
publicvoid init(){
}
/**
* 這個類是內部類,但用static修飾相當於外部類,他的名稱是:ConditionCommunicate.Business
*/
staticclass Business{
Lock lock = new ReentrantLock();
Condition condition1 = lock.newCondition();
Condition condition2 = lock.newCondition();
Condition condition3 = lock.newCondition();
privateintshouldSub = 1;
publicvoid sub2(inti){
lock.lock();
try{
while(shouldSub != 2){
try {
condition2.await();
// this.wait(); //wait和notify必須在synchronized內部使用
} catch (Exception e) {
e.printStackTrace();
}
}
for(intj = 0 ; j< 10; j++){
System.out.println("sub2 Thread cycle of "+ j +", loop of "+ i);
}
shouldSub = 3;
condition3.signal();
// this.notify();
}finally{
lock.unlock();
}
}
publicvoid sub3(inti){
lock.lock();
try{
while(shouldSub != 3){
try {
condition3.await();
// this.wait(); //wait和notify必須在synchronized內部使用
} catch (Exception e) {
e.printStackTrace();
}
}
for(intj = 0 ; j< 4; j++){
System.out.println("sub3 Thread cycle of "+ j +", loop of "+ i);
}
shouldSub = 1;
condition1.signal();
// this.notify();
}finally{
lock.unlock();
}
}
publicvoid main(inti){
lock.lock();
try{
//這裏while要比if好,會防止僞喚醒。
while(shouldSub != 1){
try {
// this.wait();
condition1.await();
} catch (Exception e) {
e.printStackTrace();
}
}
for(intj = 0 ; j< 5; j++){
System.out.println("main Thread cycle of "+ j +", loop of "+ i);
}
shouldSub = 2;
// this.notify();
condition2.signal();
}finally{
lock.unlock();
}
}
}
}