線程范圍的共享變量
多個(gè)業(yè)務(wù)模塊針對(duì)同一個(gè)static變量的操作 要保證在不同線程中 各模塊操作的是自身對(duì)應(yīng)的變量對(duì)象
public class ThreadScopeSharaData {
private static int data = 0 ;
public static void main(String[] args) {
for(int i = 0 ;i<2 ;i++){
new Thread(new Runnable(){
@Override
public void run() {
data = new Random().nextInt();
System.out.println(Thread.currentThread().getName()+ " put random data:"+data);
new A().get() ;
new B().get() ;
}
}).start() ;
}
}
static class A {
public int get(){
System.out.println("A from " + Thread.currentThread().getName()
+ " get data :" + data);
return data ;
}
}
static class B{
public int get(){
System.out.println("B from " + Thread.currentThread().getName()
+ " get data :" + data);
return data ;
}
}
}
模塊A ，B都需要訪問(wèn)static的變量data 在線程0中會(huì)隨機(jī)生成一個(gè)data值 假設(shè)為10 那么此時(shí)模塊A和模塊B在線程0中得到的data的值為10 加袋；在線程1中 假設(shè)會(huì)為data賦值為20 那么在當(dāng)前線程下
模塊A和模塊B得到data的值應(yīng)該為20
看程序執(zhí)行的結(jié)果：
Thread-0 put random data:-2009009251
Thread-1 put random data:-2009009251
A from Thread-0 get data :-2009009251
A from Thread-1 get data :-2009009251
B from Thread-0 get data :-2009009251
B from Thread-1 get data :-2009009251
Thread-0 put random data:-2045829602
Thread-1 put random data:-1842611697
A from Thread-0 get data :-1842611697
A from Thread-1 get data :-1842611697
B from Thread-0 get data :-1842611697
B from Thread-1 get data :-1842611697
會(huì)出現(xiàn)兩種情況
1.由于線程執(zhí)行速度捌袜，新的隨機(jī)值將就的隨機(jī)值覆蓋 data 值一樣
2.data 值不一樣割按，但 A、B線程都
1.使用Map實(shí)現(xiàn)線程范圍內(nèi)數(shù)據(jù)的共享
可是將data數(shù)據(jù)和當(dāng)前允許的線程綁定在一塊，在模塊A和模塊B去獲取數(shù)據(jù)data的時(shí)候 是通過(guò)當(dāng)前所屬的線程去取得data的結(jié)果就行了巴比。
聲明一個(gè)Map集合 集合的Key為Thread 存儲(chǔ)當(dāng)前所屬線程 Value 保存data的值，代碼如下：
public class ThreadScopeSharaData {
private static Map<Thread, Integer> threadData = new HashMap<>();
public static void main(String[] args) {
for (int i = 0; i < 2; i++) {
new Thread(new Runnable() {
@Override
public void run() {
int data = new Random().nextInt();
System.out.println(Thread.currentThread().getName() + " put random data:" + data);
threadData.put(Thread.currentThread(), data);
new A().get();
new B().get();
}
}).start();
}
}
static class A {
public void get() {
int data = threadData.get(Thread.currentThread());
System.out.println("A from " + Thread.currentThread().getName() + " get data:" + data);
}
}
static class B {
public void get() {
int data = threadData.get(Thread.currentThread());
System.out.println("B from " + Thread.currentThread().getName() + " get data:" + data);
}
}
}
Thread-0 put random data:-123490895
Thread-1 put random data:-1060992440
A from Thread-0 get data:-123490895
A from Thread-1 get data:-1060992440
B from Thread-0 get data:-123490895
B from Thread-1 get data:-1060992440
2.ThreadLocal實(shí)現(xiàn)線程范圍內(nèi)數(shù)據(jù)的共享
(1)訂單處理包含一系列操作：減少庫(kù)存量礁遵、增加一條流水臺(tái)賬轻绞、修改總賬，這幾個(gè)操作要在同一個(gè)事務(wù)中完成佣耐，通常也即同一個(gè)線程中進(jìn)行處理政勃，如果累加公司應(yīng)收款的操作失敗了，則應(yīng)該把前面的操作回滾兼砖，否則奸远，提交所有操作既棺，這要求這些操作使用相同的數(shù)據(jù)庫(kù)連接對(duì)象，而這些操作的代碼分別位于不同的模塊類中懒叛。
(2)銀行轉(zhuǎn)賬包含一系列操作： 把轉(zhuǎn)出帳戶的余額減少丸冕，把轉(zhuǎn)入帳戶的余額增加，這兩個(gè)操作要在同一個(gè)事務(wù)中完成薛窥，它們必須使用相同的數(shù)據(jù)庫(kù)連接對(duì)象胖烛，轉(zhuǎn)入和轉(zhuǎn)出操作的代碼分別是兩個(gè)不同的帳戶對(duì)象的方法。
(3)例如Strut2的ActionContext拆檬，同一段代碼被不同的線程調(diào)用運(yùn)行時(shí)洪己，該代碼操作的數(shù)據(jù)是每個(gè)線程各自的狀態(tài)和數(shù)據(jù)，對(duì)于不同的線程來(lái)說(shuō)竟贯，getContext方法拿到的對(duì)象都不相同答捕，對(duì)同一個(gè)線程來(lái)說(shuō)，不管調(diào)用getContext方法多少次和在哪個(gè)模塊中g(shù)etContext方法屑那，拿到的都是同一個(gè)拱镐。
4.實(shí)驗(yàn)案例：定義一個(gè)全局共享的ThreadLocal變量，然后啟動(dòng)多個(gè)線程向該ThreadLocal變量中存儲(chǔ)一個(gè)隨機(jī)值持际，接著各個(gè)線程調(diào)用另外其他多個(gè)類的方法沃琅，這多個(gè)類的方法中讀取這個(gè)ThreadLocal變量的值，就可以看到多個(gè)類在同一個(gè)線程中共享同一份數(shù)據(jù)蜘欲。
5.實(shí)現(xiàn)對(duì)ThreadLocal變量的封裝益眉，讓外界不要直接操作ThreadLocal變量。
(1)對(duì)基本類型的數(shù)據(jù)的封裝姥份，這種應(yīng)用相對(duì)很少見(jiàn)郭脂。
(2)對(duì)對(duì)象類型的數(shù)據(jù)的封裝，比較常見(jiàn)澈歉，即讓某個(gè)類針對(duì)不同線程分別創(chuàng)建一個(gè)獨(dú)立的實(shí)例對(duì)象展鸡。
public class ThreadLocalTest {
private static ThreadLocal<Integer> threadLocal = new ThreadLocal<>();
public static void main(String[] args) {
for (int i = 0; i < 2; i++) {
new Thread(new Runnable() {
@Override
public void run() {
int data = new Random().nextInt();
System.out.println(Thread.currentThread().getName() + " put random data:" + data);
threadLocal.set(data);
new A().get();
new B().get();
}
}).start();
}
}
static class A {
public void get() {
int data = threadLocal.get();
System.out.println("A from " + Thread.currentThread().getName() + " get data:" + data);
}
}
static class B {
public void get() {
int data = threadLocal.get();
System.out.println("B from " + Thread.currentThread().getName() + " get data:" + data);
}
}
}
Thread-0 put random data:-2015900409
Thread-1 put random data:-645411160
A from Thread-0 get data:-2015900409
A from Thread-1 get data:-645411160
B from Thread-0 get data:-2015900409
B from Thread-1 get data:-645411160
優(yōu)化
public class ThreadLocalTest {
private static ThreadLocal<Integer> threadLocal = new ThreadLocal<>();
//private static ThreadLocal<MyThreadScopeData> myThreadScopeDataThreadLocal = new ThreadLocal<>();
public static void main(String[] args) {
for (int i = 0; i < 2; i++) {
new Thread(new Runnable() {
@Override
public void run() {
int data = new Random().nextInt();
System.out.println(Thread.currentThread().getName() + " put random data:" + data);
threadLocal.set(data);
// MyThreadScopeData myThreadScopeData = new MyThreadScopeData();
// myThreadScopeData.setName("name" + data);
// myThreadScopeData.setAge(data);
// myThreadScopeDataThreadLocal.set(myThreadScopeData);
//獲取與當(dāng)前線程綁定的實(shí)例并設(shè)置值
MyThreadScopeData.getThreadInstance().setName("name" + data);
MyThreadScopeData.getThreadInstance().setAge(data);
new A().get();
new B().get();
}
}).start();
}
}
static class A {
public void get() {
int data = threadLocal.get();
// MyThreadScopeData myData = myThreadScopeDataThreadLocal.get();
//
//
// System.out.println("A from " + Thread.currentThread().getName()
// + " getMyData: " + myData.getName() + "," + myData.getAge());
MyThreadScopeData myData = MyThreadScopeData.getThreadInstance();
System.out.println("A from " + Thread.currentThread().getName()
+ " getMyData: " + myData.getName() + "," + myData.getAge());
}
}
static class B {
public void get() {
int data = threadLocal.get();
//System.out.println("B from " + Thread.currentThread().getName() + " get data:" + data);
MyThreadScopeData myData = MyThreadScopeData.getThreadInstance();
System.out.println("B from " + Thread.currentThread().getName()
+ " getMyData: " + myData.getName() + "," + myData.getAge());
}
}
}
//一個(gè)綁定當(dāng)前線程的類
class MyThreadScopeData {
private static ThreadLocal<MyThreadScopeData> map = new ThreadLocal<>();
private String name;
private int age;
private MyThreadScopeData() {
}
//定義一個(gè)靜態(tài)方法，返回各線程自己的實(shí)例
//這里不必用同步埃难，因?yàn)槊總€(gè)線程都要?jiǎng)?chuàng)建自己的實(shí)例莹弊，所以沒(méi)有線程安全問(wèn)題。
public static MyThreadScopeData getThreadInstance() {
//獲取當(dāng)前線程綁定的實(shí)例
MyThreadScopeData instance = map.get();
if (instance == null) {
instance = new MyThreadScopeData();
map.set(instance);
}
return instance;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
Thread-1 put random data:-1041517189
Thread-0 put random data:-98835751
A from Thread-1 getMyData: name-1041517189,-1041517189
A from Thread-0 getMyData: name-98835751,-98835751
B from Thread-1 getMyData: name-1041517189,-1041517189
B from Thread-0 getMyData: name-98835751,-98835751
實(shí)例：
設(shè)計(jì)4個(gè)線程涡尘，其中兩個(gè)線程每次對(duì)j增加1上炎，另外兩個(gè)線程對(duì)j每次減少1搅幅，寫出程序单芜。
1矾飞、如果每個(gè)線程執(zhí)行的代碼相同，可以使用同一個(gè)Runnable對(duì)象座泳，這個(gè)Runnable對(duì)象中有那個(gè)共享數(shù)據(jù)惠昔，例如，賣票系統(tǒng)就可以這么做挑势。
public class SellTicket {
//賣票系統(tǒng)镇防，多個(gè)窗口的處理邏輯是相同的
public static void main(String[] args) {
Ticket t = new Ticket();
new Thread(t).start();
new Thread(t).start();
}
}
/**
* 將屬性和處理邏輯，封裝在一個(gè)類中
*
* @author yang
*/
class Ticket implements Runnable {
private int ticket = 10;
public synchronized void run() {
while (ticket > 0) {
ticket--;
System.out.println("當(dāng)前票數(shù)為：" + ticket);
}
}
}
2潮饱、如果每個(gè)線程執(zhí)行的代碼不同来氧，這時(shí)候需要用不同的Runnable對(duì)象，例如香拉，設(shè)計(jì)2個(gè)線程啦扬。一個(gè)線程對(duì)j增加1，另外一個(gè)線程對(duì)j減1凫碌，銀行存取款系統(tǒng)扑毡。
public class MultiThreadShareData {
private int j;
public static void main(String[] args) {
MultiThreadShareData multiThreadShareData = new MultiThreadShareData();
for(int i=0;i<2;i++){
new Thread(multiThreadShareData.new ShareData1()).start();//增加
new Thread(multiThreadShareData.new ShareData2()).start();//減少
}
}
//自增
private synchronized void Inc(){
j++;
System.out.println(Thread.currentThread().getName()+" inc "+j);
}
//自減
private synchronized void Dec(){
j--;
System.out.println(Thread.currentThread().getName()+" dec "+j);
}
class ShareData1 implements Runnable {
public void run() {
for(int i=0;i<5;i++){
Inc();
}
}
}
class ShareData2 implements Runnable {
public void run() {
for(int i=0;i<5;i++){
Dec();
}
}
}
}
Thread-0 inc 1
Thread-0 inc 2
Thread-0 inc 3
Thread-0 inc 4
Thread-0 inc 5
Thread-1 dec 4
Thread-1 dec 3
Thread-2 inc 4
Thread-2 inc 5
Thread-2 inc 6
Thread-2 inc 7
Thread-2 inc 8
Thread-1 dec 7
Thread-1 dec 6
Thread-1 dec 5
Thread-3 dec 4
Thread-3 dec 3
Thread-3 dec 2
Thread-3 dec 1
Thread-3 dec 0
特別感謝：
JAVA 并發(fā)編程-多個(gè)線程之間共享數(shù)據(jù)
多線程：（五）多個(gè)線程之間共享數(shù)據(jù)
