定義:
Balking模式也有守護條件,如果守護條件不成立,立即中斷處理。
引例
名字 | 說明 |
Data | |
SaverThread | |
ChangeThread | |
Main |
public class Data {
private String filename; //修改是的名字
private String content; // 資料的內容
private boolean changed; //修改後的內容還沒存儲的話,值爲true
public Data(String filename, String content) {
this.filename = filename;
this.content = content;
this.changed = true;
}
// 修改資料內容
public synchronized void change(String newContent) {
content = newContent;
changed = true;
}
// 若有資料修改,就存儲到擋安裏
public synchronized void save() throws IOException {
if (!changed) {
System.out.println(Thread.currentThread().getName() + " balks");
return;
}
doSave();
changed = false;
}
// 實際資料儲存到擋案裏用的方法
private void doSave() throws IOException {
System.out.println(Thread.currentThread().getName() + " calls doSave, content = " + content);
Writer writer = new FileWriter(filename);
writer.write(content);
writer.close();
}
}
public class SaverThread extends Thread {
private Data data;
public SaverThread(String name, Data data) {
super(name);
this.data = data;
}
public void run() {
try {
while (true) {
data.save(); // 存儲資料
Thread.sleep(1000); // 休息約1秒
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public class ChangerThread extends Thread {
private Data data;
private Random random = new Random();
public ChangerThread(String name, Data data) {
super(name);
this.data = data;
}
public void run() {
try {
for (int i = 0; true; i++) {
data.change("No." + i); //修改資料
Thread.sleep(random.nextInt(1000)); // 模擬去做別的事情
data.save(); // 明確的要求存檔
}
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
public class Main {
public static void main(String[] args) {
Data data = new Data("data.txt", "(empty)");
new ChangerThread("ChangerThread", data).start();
new SaverThread("SaverThread", data).start();
}
}
結果:
SaverThread calls doSave, content = No.0
ChangerThread balks
ChangerThread calls doSave, content = No.1
SaverThread calls doSave, content = No.2
ChangerThread balks
ChangerThread calls doSave, content = No.3
ChangerThread calls doSave, content = No.4
SaverThread calls doSave, content = No.5
Balking模式角色
GuardedObject(被守護的對象)是一個持有被守護方法的類。當線程執行守護方法時,若守護條件成立則執行,若不成立則直接返回。守護條件的成立會隨着被守護的對象狀態發生改變。
何時使用Balking模式
並不需要執行時、不需要等待守護條件時、守護條件僅在第一次成立時
tips:
synchronized中沒有超時,也不能中斷