java 线程 设计模式_Java多线程设计模式（四）
Future Pattern
在Thread-Per-Message Pattern中，我們研究過(guò)“收到每個(gè)請(qǐng)求建立一個(gè)線(xiàn)程”的做法，但這樣的請(qǐng)求是不要求有返回值的。如果當(dāng)需要返回值，但由于后臺(tái)處理需要很久，返回值 不能馬上獲取，那么就可以使用 Future Pattern。Future Pattern同樣會(huì)每個(gè)請(qǐng)求建立一個(gè)線(xiàn)程處理，同時(shí)會(huì)馬上返回一個(gè)對(duì)象，但該對(duì)象并不是真正的返回值，真正的返回值可能現(xiàn)在還沒(méi)有準(zhǔn)備好，不過(guò)客戶(hù)端可 以根據(jù)這個(gè)返回對(duì)象，在之后的時(shí)間來(lái)獲取真正的返回值。
public?interface?Data?{
public?String?getContent();
}
public?class?RealData?implements?Data?{
private?String?content;
public?RealData(int?count,?char?c)?{
System.out.println("making?RealData("?+?count?+?",?"?+?c?+?")?Begin.");
char[]?buffer?=?new?char[count];
for?(int?i?=?0;?i?
buffer[i]?=?c;
slowly();
}
this.content?=?String.valueOf(buffer);
System.out.println("making?RealData("?+?count?+?",?"?+?c?+?")?End.");
}
@Override
public?String?getContent()?{
return?this.content;
}
private?void?slowly()?{
try?{
Thread.sleep(100);
}?catch?(InterruptedException?e)?{
}
}
}
public?class?FutureData?implements?Data?{
private?RealData?realData;
private?boolean??ready?=?false;
public?synchronized?void?setRealData(RealData?realData)?{
if?(ready)?{
return;
}
this.realData?=?realData;
this.ready?=?true;
notifyAll();
}
@Override
public?synchronized?String?getContent()?{
while?(!ready)?{
try?{
wait();
}?catch?(InterruptedException?e)?{
}
}
return?this.realData.getContent();
}
}
public?class?Host?{
public?Data?handle(final?int?count,?final?char?c)?{
System.out.println("handle?(?"?+?count?+?",?"?+?c?+?")?Begin.");
final?FutureData?futureData?=?new?FutureData();
new?Thread()?{
@Override
public?void?run()?{
RealData?realData?=?new?RealData(count,?c);
futureData.setRealData(realData);
}
}.start();
System.out.println("handle?(?"?+?count?+?",?"?+?c?+?")?End.");
return?futureData;
}
}
public?class?Main?{
public?static?void?main(String[]?args)?{
System.out.println("main?Begin.");
Host?host?=?new?Host();
Data?data1?=?host.handle(10,?'a');
Data?data2?=?host.handle(20,?'b');
Data?data3?=?host.handle(30,?'c');
System.out.println("main?other?job?Begin.");
try?{
Thread.sleep(2000);
}?catch?(InterruptedException?e)?{
}
System.out.println("main?other?job?End.");
System.out.println("data1?=?"?+?data1.getContent());
System.out.println("data2?=?"?+?data2.getContent());
System.out.println("data3?=?"?+?data3.getContent());
System.out.println("main?End.");
}
}
在Worker Thread Pattern中，我們討論過(guò)“方法調(diào)用”和“方法執(zhí)行”的分離。而Future Pattern 分離了“準(zhǔn)備返回值”和“使用返回值”。我們?cè)贔uttern Pattern中，可以看到設(shè)計(jì)模式Proxy Pattern的實(shí)現(xiàn)。
Two-Phase Termination Pattern
Two-Phase Termination
Pattern很簡(jiǎn)單，但該模式提供了一種結(jié)束線(xiàn)程的優(yōu)雅方法。java.lang.Thread類(lèi)有一個(gè)用來(lái)強(qiáng)制結(jié)束掉線(xiàn)程的stop()方法。但是
stop方法已經(jīng)不建議使用(deprecated)，原因是stop()方法會(huì)使實(shí)例喪失安全性的保障。使用stop()方法時(shí)，線(xiàn)程會(huì)拋出
java.lang.ThreadDeath異常而馬上結(jié)束，即使該線(xiàn)程現(xiàn)在正在執(zhí)行靈界區(qū)間(例如synchronized方法的中間)，也會(huì)馬上結(jié)
束。
public?class?CountupThread?extends?Thread?{
private?boolean?isShutdown?=?false;
private?int?????count??????=?0;
@Override
public?void?run()?{
try?{
while?(isShutdown)?{
doWork();
}
}?catch?(InterruptedException?e)?{
}?finally?{
doShutdown();
}
}
public?void?shutdownReqeust()?{
this.isShutdown?=?true;
interrupt();
}
private?void?doShutdown()?{
System.out.println("doShutdown:?current?count?is?"?+?this.count);
}
private?void?doWork()?throws?InterruptedException?{
System.out.println("curren?count?is?"?+?++count);
Thread.sleep(500);
}
public?static?void?main(String[]?args)?{
System.out.println("main?Begin.");
CountupThread?countupThread?=?new?CountupThread();
countupThread.start();
try?{
Thread.sleep(100000);
}?catch?(InterruptedException?e)?{
}
System.out.println("main?:?shutdown?request.");
countupThread.shutdownReqeust();
System.out.println("main?:?join");
//?等待線(xiàn)程結(jié)束
try?{
countupThread.join();
}?catch?(InterruptedException?e)?{
}
System.out.println("main?End.");
}
}
Thread-Specific Storage Pattern
Thread-Specific Storage
Pattern就是“線(xiàn)程獨(dú)有的存儲(chǔ)庫(kù)”、“針對(duì)每個(gè)線(xiàn)程提供的內(nèi)存空間”的意義。java.lang.ThreadLocal的實(shí)例可以想象成一種集合
架構(gòu)(collection)或許會(huì)比較好理解。ThreadLocal的實(shí)例只有一個(gè)，管理多個(gè)對(duì)象。
public?class?Log?{
private?static?final?ThreadLocal?tsLogCollection?=?new?ThreadLocal();
public?static?void?println(String?s)?{
getTSLog().printWrite(s);
}
public?static?void?close()?{
getTSLog().close();
}
private?static?TSLog?getTSLog()?{
TSLog?tsLog?=?tsLogCollection.get();
//?如果線(xiàn)程時(shí)第一次調(diào)用，新建立新文件并注冊(cè)log
if?(tsLog?==?null)?{
tsLog?=?new?TSLog(Thread.currentThread().getName()?+?"-log.txt");
tsLogCollection.set(tsLog);
}
return?tsLog;
}
}
import?java.io.FileNotFoundException;
import?java.io.PrintWriter;
public?class?TSLog?{
private?PrintWriter?writer;
public?TSLog(String?filename)?{
try?{
this.writer?=?new?PrintWriter(filename);
}?catch?(FileNotFoundException?e)?{
}
}
public?void?printWrite(String?s)?{
writer.println(s);
}
public?void?close()?{
writer.println("===========End?of?log===========");
writer.close();
}
}
public?class?ClientThread?extends?Thread?{
public?ClientThread(String?name)?{
super(name);
}
@Override
public?void?run()?{
System.out.println(getName()?+?"?Begin.");
for?(int?i?=?0;?i?
Log.println("i?=?"?+?i);
try?{
Thread.sleep(100);
}?catch?(InterruptedException?e)?{
}
}
Log.close();
System.out.println(getName()?+?"?End.");
}
public?static?void?main(String[]?args)?{
new?ClientThread("Alice").start();
new?ClientThread("Bobby").start();
new?ClientThread("Chris").start();
}
}
Active Object Pattern
Active Object
Pattern其實(shí)可以看作是多個(gè)多線(xiàn)程模式和多個(gè)設(shè)計(jì)模式組合成的一種更高級(jí)的模式，里面多個(gè)對(duì)象各司其職，共同協(xié)作。Active Object
Pattern里面使用到了Producer-Consumer Pattern、Thread-Per-Message Pattern、Future
Pattern和設(shè)計(jì)模式的Proxy Pattern、Command Pattern等。
Server端代碼：
public?interface?ActiveObject?{
public?Result?makeString(int?count,?char?fillchar);
public?void?displayString(String?string);
}
public?class?Proxy?implements?ActiveObject?{
private?SchedulerThread?scheduler;
private?Servant?????????servant;
public?Proxy(SchedulerThread?scheduler,?Servant?servant)?{
this.scheduler?=?scheduler;
this.servant?=?servant;
}
@Override
public?Result?makeString(int?count,?char?fillchar)?{
FutureResult?future?=?new?FutureResult();
MakeStringRequest?request?=?new?MakeStringRequest(servant,?future,?count,?fillchar);
this.scheduler.invoke(request);
return?future;
}
@Override
public?void?displayString(String?string)?{
DisplayStringRequest?request?=?new?DisplayStringRequest(servant,?string);
this.scheduler.invoke(request);
}
}
public?class?Servant?implements?ActiveObject?{
@Override
public?Result?makeString(int?count,?char?fillchar)?{
char[]?buffer?=?new?char[count];
for?(int?i?=?0;?i?
buffer[i]?=?fillchar;
try?{
Thread.sleep(500);
}?catch?(InterruptedException?e)?{
}
}
RealResult?result?=?new?RealResult(String.valueOf(buffer));
return?result;
}
@Override
public?void?displayString(String?string)?{
System.out.println("displayString(?"?+?string?+?"?)");
try?{
Thread.sleep(10);
}?catch?(InterruptedException?e)?{
}
}
}
public?interface?Result?{
public?String?getResultValue();
}
public?class?FutureResult?implements?Result?{
private?Result??result;
private?boolean?isReady?=?false;
public?synchronized?void?setResult(Result?result)?{
if?(isReady)?{
return;
}
this.result?=?result;
this.isReady?=?true;
notifyAll();
}
@Override
public?synchronized?String?getResultValue()?{
while?(!isReady)?{
try?{
wait();
}?catch?(InterruptedException?e)?{
}
}
return?result.getResultValue();
}
}
public?class?RealResult?implements?Result?{
private?String?resultValue;
public?RealResult(String?resultValue)?{
this.resultValue?=?resultValue;
}
@Override
public?String?getResultValue()?{
return?this.resultValue;
}
}
public?abstract?class?MethodRequest?{
protected?final?Servant??????servant;
protected?final?FutureResult?future;
public?MethodRequest(Servant?servant,?FutureResult?future)?{
this.servant?=?servant;
this.future?=?future;
}
public?abstract?void?execute();
}
public?class?MakeStringRequest?extends?MethodRequest?{
private?int??count;
private?char?fillchar;
public?MakeStringRequest(Servant?servant,?FutureResult?future,?int?count,?char?fillchar)?{
super(servant,?future);
this.count?=?count;
this.fillchar?=?fillchar;
}
@Override
public?void?execute()?{
Result?result?=?this.servant.makeString(count,?fillchar);
future.setResult(result);
}
}
public?class?DisplayStringRequest?extends?MethodRequest?{
private?String?string;
public?DisplayStringRequest(Servant?servant,?String?string)?{
super(servant,?null);
this.string?=?string;
}
@Override
public?void?execute()?{
this.servant.displayString(string);
}
}
public?class?SchedulerThread?extends?Thread?{
private?ActivationQueue?queue?=?new?ActivationQueue();
public?void?invoke(MethodRequest?request)?{
this.queue.putRequest(request);
}
@Override
public?void?run()?{
while?(true)?{
this.queue.takeRequest().execute();
}
}
}
package?activeobject.server;
import?java.util.LinkedList;
public?class?ActivationQueue?{
private?final?LinkedList?requestQueue?=?new?LinkedList();
private?final?int???????????????????????queueSize????=?100;
public?synchronized?void?putRequest(MethodRequest?request)?{
while?(this.requestQueue.size()?>=?queueSize)?{
try?{
wait();
}?catch?(InterruptedException?e)?{
}
}
this.requestQueue.addLast(request);
notifyAll();
}
public?synchronized?MethodRequest?takeRequest()?{
while?(this.requestQueue.size()?==?0)?{
try?{
wait();
}?catch?(InterruptedException?e)?{
}
}
MethodRequest?request?=?this.requestQueue.removeFirst();
notifyAll();
return?request;
}
}
public?class?ActiveObjectFactory?{
public?static?ActiveObject?createActiveObjcet()?{
Servant?servant?=?new?Servant();
SchedulerThread?scheduler?=?new?SchedulerThread();
Proxy?proxy?=?new?Proxy(scheduler,?servant);
scheduler.start();
return?proxy;
}
}
UML如下圖：
客戶(hù)端代碼：
import?activeobject.server.ActiveObject;
public?class?DisplayClientThread?extends?Thread?{
private?ActiveObject?activeObj;
public?DisplayClientThread(String?name,?ActiveObject?activeObj)?{
super(name);
this.activeObj?=?activeObj;
}
@Override
public?void?run()?{
int?i?=?0;
while?(true)?{
i++;
String?string?=?getName()?+?"?No."?+?i;
activeObj.displayString(string);
}
}
}
import?activeobject.server.ActiveObject;
import?activeobject.server.Result;
public?class?MakerClientThread?extends?Thread?{
private?final?ActiveObject?activeObj;
private?final?char?????????fillchar;
public?MakerClientThread(String?name,?ActiveObject?activeObj)?{
super(name);
this.activeObj?=?activeObj;
this.fillchar?=?name.charAt(0);
}
@Override
public?void?run()?{
int?i?=?0;
while?(true)?{
i++;
Result?result?=?activeObj.makeString(i,?fillchar);
try?{
Thread.sleep(1000);
}?catch?(InterruptedException?e)?{
}
String?resultValue?=?result.getResultValue();
System.out.println(Thread.currentThread().getName()?+?":value?=?"?+?resultValue);
}
}
}
import?activeobject.server.ActiveObject;
import?activeobject.server.ActiveObjectFactory;
public?class?Main?{
public?static?void?main(String[]?args)?{
ActiveObject?activeObj?=?ActiveObjectFactory.createActiveObjcet();
new?MakerClientThread("Alice",?activeObj).start();
new?MakerClientThread("Bobby",?activeObj).start();
new?DisplayClientThread("Chris",?activeObj).start();
}
}
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