線程范圍的共享變量
多個業務模塊針對同一個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應的變量對象
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static的變量data 在線程0中會隨機生成一個data值 假設為10 那么此時模塊A和模塊B在線程0中得到的data的值為10 ；在線程1中 假設會為data賦值為20 那么在當前線程下
模塊A和模塊B得到data的值應該為20
看程序執行的結果：
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
會出現兩種情況
1.由于線程執行速度，新的隨機值將就的隨機值覆蓋 data 值一樣
2.data 值不一樣，但 A、B線程都
1.使用Map實現線程范圍內數據的共享
可是將data數據和當前允許的線程綁定在一塊，在模塊A和模塊B去獲取數據data的時候 是通過當前所屬的線程去取得data的結果就行了。
聲明一個Map集合 集合的Key為Thread 存儲當前所屬線程 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實現線程范圍內數據的共享
(1)訂單處理包含一系列操作：減少庫存量、增加一條流水臺賬、修改總賬，這幾個操作要在同一個事務中完成，通常也即同一個線程中進行處理，如果累加公司應收款的操作失敗了，則應該把前面的操作回滾，否則，提交所有操作，這要求這些操作使用相同的數據庫連接對象，而這些操作的代碼分別位于不同的模塊類中。
(2)銀行轉賬包含一系列操作： 把轉出帳戶的余額減少，把轉入帳戶的余額增加，這兩個操作要在同一個事務中完成，它們必須使用相同的數據庫連接對象，轉入和轉出操作的代碼分別是兩個不同的帳戶對象的方法。
(3)例如Strut2的ActionContext，同一段代碼被不同的線程調用運行時，該代碼操作的數據是每個線程各自的狀態和數據，對于不同的線程來說，getContext方法拿到的對象都不相同，對同一個線程來說，不管調用getContext方法多少次和在哪個模塊中getContext方法，拿到的都是同一個。
4.實驗案例：定義一個全局共享的ThreadLocal變量，然后啟動多個線程向該ThreadLocal變量中存儲一個隨機值，接著各個線程調用另外其他多個類的方法，這多個類的方法中讀取這個ThreadLocal變量的值，就可以看到多個類在同一個線程中共享同一份數據。
5.實現對ThreadLocal變量的封裝，讓外界不要直接操作ThreadLocal變量。
(1)對基本類型的數據的封裝，這種應用相對很少見。
(2)對對象類型的數據的封裝，比較常見，即讓某個類針對不同線程分別創建一個獨立的實例對象。
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);
//獲取與當前線程綁定的實例并設置值
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());
}
}
}
//一個綁定當前線程的類
class MyThreadScopeData {
private static ThreadLocal<MyThreadScopeData> map = new ThreadLocal<>();
private String name;
private int age;
private MyThreadScopeData() {
}
//定義一個靜態方法，返回各線程自己的實例
//這里不必用同步，因為每個線程都要創建自己的實例，所以沒有線程安全問題。
public static MyThreadScopeData getThreadInstance() {
//獲取當前線程綁定的實例
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
實例：
設計4個線程，其中兩個線程每次對j增加1，另外兩個線程對j每次減少1，寫出程序。
1、如果每個線程執行的代碼相同，可以使用同一個Runnable對象，這個Runnable對象中有那個共享數據，例如，賣票系統就可以這么做。
public class SellTicket {
//賣票系統，多個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，封裝在一個類中
*
* @author yang
*/
class Ticket implements Runnable {
private int ticket = 10;
public synchronized void run() {
while (ticket > 0) {
ticket--;
System.out.println("當前票數為：" + ticket);
}
}
}
2、如果每個線程執行的代碼不同，這時候需要用不同的Runnable對象，例如，設計2個線程。一個線程對j增加1，另外一個線程對j減1，銀行存取款系統。
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
