多線程之間實現通訊
多線程之間如何實現通訊
什麼是多線程之間通訊?
多線程之間通訊,其實就是多個線程在操作同一個資源,但是操作的動作不同。
畫圖演示
多線程之間通訊需求
需求:第一個線程寫入(input)用戶,另一個線程取讀取(out)用戶.實現讀一個,寫一個操作。
代碼實現基本實現
共享資源源實體類
class Res { public String userSex; public String userName; } |
輸入線程資源
class IntThrad extends Thread { private Res res;
public IntThrad(Res res) { this.res = res; }
@Override public void run() { int count = 0; while (true) { if (count == 0) { res.userName = "餘勝軍"; res.userSex = "男"; } else { res.userName = "小紅"; res.userSex = "女"; } count = (count + 1) % 2; } } }
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輸出線程
class OutThread extends Thread { private Res res;
public OutThread(Res res) { this.res = res; }
@Override public void run() { while (true) { System.out.println(res.userName + "--" + res.userSex); } } } |
運行代碼
Res res = new Res(); IntThrad intThrad = new IntThrad(res); OutThread outThread = new OutThread(res); intThrad.start(); outThread.start(); |
運行代碼
注意:數據發生錯亂,造成線程安全問題
解決線程安全問題
IntThrad 加上synchronized
class IntThrad extends Thread { private Res res;
public IntThrad(Res res) { this.res = res; }
@Override public void run() { int count = 0; while (true) { synchronized (res) { if (count == 0) { res.userName = "餘勝軍"; res.userSex = "男"; } else { res.userName = "小紅"; res.userSex = "女"; } count = (count + 1) % 2; }
} } } |
輸出線程加上synchronized
class Res { public String userName; public String sex; }
class InputThread extends Thread { private Res res;
public InputThread(Res res) { this.res = res; }
@Override public void run() { int count = 0; while (true) { synchronized (res) { if (count == 0) { res.userName = "餘勝軍"; res.sex = "男"; } else { res.userName = "小紅"; res.sex = "女"; } count = (count + 1) % 2; }
} } }
class OutThrad extends Thread { private Res res;
public OutThrad(Res res) { this.res = res; }
@Override public void run() { while (true) { synchronized (res) { System.out.println(res.userName + "," + res.sex); } }
} }
public class ThreadDemo01 {
public static void main(String[] args) { Res res = new Res(); InputThread inputThread = new InputThread(res); OutThrad outThrad = new OutThrad(res); inputThread.start(); outThrad.start(); }
}
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wait、notify方法
1.因爲涉及到對象鎖,他們必須都放在synchronized中來使用. Wait、Notify一定要在synchronized裏面進行使用。
2.Wait必須暫定當前正在執行的線程,並釋放資源鎖,讓其他線程可以有機會運行
3. notify/notifyall: 喚醒因鎖池中的線程,使之運行
注意:一定要在線程同步中使用,並且是同一個鎖的資源
class Res { public String userSex; public String userName; //線程通訊標識 public boolean flag = false; }
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class IntThrad extends Thread { private Res res;
public IntThrad(Res res) { this.res = res; }
@Override public void run() { int count = 0; while (true) { synchronized (res) { if (res.flag) { try { // 當前線程變爲等待,但是可以釋放鎖 res.wait(); } catch (Exception e) {
} } if (count == 0) { res.userName = "餘勝軍"; res.userSex = "男"; } else { res.userName = "小紅"; res.userSex = "女"; } count = (count + 1) % 2; res.flag = true; // 喚醒當前線程 res.notify(); }
} } } |
class OutThread extends Thread { private Res res;
public OutThread(Res res) { this.res = res; }
@Override public void run() { while (true) { synchronized (res) { if (!res.flag) { try { res.wait(); } catch (Exception e) { // TODO: handle exception } } System.out.println(res.userName + "--" + res.userSex); res.flag = false; res.notify(); } } } } |
public class ThreaCommun { public static void main(String[] args) { Res res = new Res(); IntThrad intThrad = new IntThrad(res); OutThread outThread = new OutThread(res); intThrad.start(); outThread.start(); } } |
wait與sleep區別
對於sleep()方法,我們首先要知道該方法是屬於Thread類中的。而wait()方法,則是屬於Object類中的。
sleep()方法導致了程序暫停執行指定的時間,讓出cpu該其他線程,但是他的監控狀態依然保持者,當指定的時間到了又會自動恢復運行狀態。
在調用sleep()方法的過程中,線程不會釋放對象鎖。
而當調用wait()方法的時候,線程會放棄對象鎖,進入等待此對象的等待鎖定池,只有針對此對象調用notify()方法後本線程才進入對象鎖定池準備
獲取對象鎖進入運行狀態。
Lock鎖
在 jdk1.5 之後,併發包中新增了 Lock 接口(以及相關實現類)用來實現鎖功能,Lock 接口提供了與 synchronized 關鍵字類似的同步功能,但需要在使用時手動獲取鎖和釋放鎖。
Lock寫法
Lock lock = new ReentrantLock(); lock.lock(); try{ //可能會出現線程安全的操作 }finally{ //一定在finally中釋放鎖 //也不能把獲取鎖在try中進行,因爲有可能在獲取鎖的時候拋出異常 lock.ublock(); }
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Lock與synchronized 關鍵字的區別
Lock 接口可以嘗試非阻塞地獲取鎖 當前線程嘗試獲取鎖。如果這一時刻鎖沒有被其他線程獲取到,則成功獲取並持有鎖。
Lock 接口能被中斷地獲取鎖 與 synchronized 不同,獲取到鎖的線程能夠響應中斷,當獲取到的鎖的線程被中斷時,中斷異常將會被拋出,同時鎖會被釋放。
Lock 接口在指定的截止時間之前獲取鎖,如果截止時間到了依舊無法獲取鎖,則返回。
Condition用法
Condition的功能類似於在傳統的線程技術中的,Object.wait()和Object.notify()的功能。
代碼
Condition condition = lock.newCondition(); res. condition.await(); 類似wait res. Condition. Signal() 類似notify |
class Res { public String userName; public String sex; public boolean flag = false; Lock lock = new ReentrantLock(); }
class InputThread extends Thread { private Res res; Condition newCondition; public InputThread(Res res, Condition newCondition) { this.res = res; this.newCondition=newCondition; }
@Override public void run() { int count = 0; while (true) { // synchronized (res) {
try { res.lock.lock(); if (res.flag) { try { // res.wait(); newCondition.await(); } catch (Exception e) { // TODO: handle exception } } if (count == 0) { res.userName = "餘勝軍"; res.sex = "男"; } else { res.userName = "小紅"; res.sex = "女"; } count = (count + 1) % 2; res.flag = true; // res.notify(); newCondition.signal(); } catch (Exception e) { // TODO: handle exception }finally { res.lock.unlock(); } }
// } } }
class OutThrad extends Thread { private Res res; private Condition newCondition; public OutThrad(Res res,Condition newCondition) { this.res = res; this.newCondition=newCondition; }
@Override public void run() { while (true) { // synchronized (res) { try { res.lock.lock(); if (!res.flag) { try { // res.wait(); newCondition.await(); } catch (Exception e) { // TODO: handle exception } } System.out.println(res.userName + "," + res.sex); res.flag = false; // res.notify(); newCondition.signal(); } catch (Exception e) { // TODO: handle exception }finally { res.lock.unlock(); } // } }
} }
public class ThreadDemo01 {
public static void main(String[] args) { Res res = new Res(); Condition newCondition = res.lock.newCondition(); InputThread inputThread = new InputThread(res,newCondition); OutThrad outThrad = new OutThrad(res,newCondition); inputThread.start(); outThrad.start(); }
}
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