Activity中运用线程的例子

Activity中使用线程的例子

转自：http://blog.csdn.net/yihui823/article/details/6741411

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今天看到一段很糟糕的代码。于是做了一个工程，模拟这段代码，向大家说明一下线程在使用中要注意的几点。这个例子适合给新手，也欢迎各位高手来指点一下。

首先，上代码。

第一个类LoginService，这是一个模拟类，把业务剥离出去了。只是模拟登录操作而已。

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[java]?view plaincopy

1. package?com.study;??
2. package?com.study;??
3. ??
4. /**?
5. ?*?虚拟的一个登录服务.?
6. ?*?@author?yihui823?
7. ?*/??
8. public?class?LoginService?{??
9. ??
10. ????//单例??
11. ????private?static?LoginService?oneInstance?=?new?LoginService();??
12. ??????
13. ????/**?
14. ?????*?得到唯一的一个单例?
15. ?????*?@return?唯一的一个单例?
16. ?????*/??
17. ????public?static?LoginService?getInstance()?{??
18. ????????return?oneInstance;??
19. ????}??
20. ??????
21. ????//登录成功标记??
22. ????private?boolean?hadLogin?=?false;??
23. ??????
24. ????/**?
25. ?????*?模拟登录操作?
26. ?????*?@return?true:登录成功?
27. ?????*/??
28. ????public?boolean?login()?{??
29. ????????try?{??
30. ????????????Thread.sleep(2000);??
31. ????????}?catch?(InterruptedException?e)?{??
32. ????????}??
33. ????????hadLogin?=?true;??
34. ????????return?hadLogin;??
35. ????}??
36. ??????
37. ????/**?
38. ?????*?判断是否登录?
39. ?????*?@return?true:已经登录?
40. ?????*/??
41. ????public?boolean?isLogin()?{??
42. ????????return?hadLogin;??
43. ????}??
44. }??

第二个类就是我们的Activity了。

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[java]?view plaincopy

1. package?com.study;??
2. ??
3. import?android.app.Activity;??
4. import?android.os.Bundle;??
5. import?android.widget.Toast;??
6. ??
7. /**?
8. ?*?一个段不好的代码?
9. ?*?@author?yihui823?
10. ?*/??
11. public?class?BadCodeActivity?extends?Activity?{??
12. ??????
13. ????//登录服务??
14. ????private?LoginService?lService?=?LoginService.getInstance();??
15. ??????
16. ????/**?Called?when?the?activity?is?first?created.?*/??
17. ????@Override??
18. ????public?void?onCreate(Bundle?savedInstanceState)?{??
19. ????????super.onCreate(savedInstanceState);??
20. ????????setContentView(R.layout.main);??
21. ??
22. ????????new?Thread(new?Runnable()?{??
23. ????????????@Override??
24. ????????????public?void?run()?{??
25. ????????????????while(!lService.isLogin()?)?{??
26. ????????????????????try?{??
27. ????????????????????????lService.login();??
28. ????????????????????????Thread.sleep(1000);??
29. ????????????????????}?catch?(InterruptedException?e)?{??
30. ????????????????????????e.printStackTrace();??
31. ????????????????????}??
32. ????????????????}??
33. ????????????????Toast.makeText(BadCodeActivity.this,?"登录成功",?Toast.LENGTH_LONG).show();??
34. ????????????}??
35. ????????}).start();??
36. ????}??
37. }??

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1. <span?style="background-color:?rgb(255,?255,?255);">这个例子呢，显然运行的时候会报错的。请见我的另一篇文章：<a?href="http://blog.csdn.net/yihui823/article/details/6722784"?target="_blank">Android画面UI中的线程约束</a>。我们在非UI线程里去控制UI界面，就必须使用Handler来发送消息。修改代码如下：</span>??

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[java]?view plaincopy

1. package?com.study;??
2. ??
3. import?android.app.Activity;??
4. import?android.os.Bundle;??
5. import?android.os.Handler;??
6. import?android.os.Message;??
7. import?android.widget.Toast;??
8. ??
9. /**?
10. ?*?一个段不好的代码?
11. ?*?@author?yihui823?
12. ?*/??
13. public?class?BadCodeActivity?extends?Activity?{??
14. ??????
15. ????//登录服务??
16. ????private?LoginService?lService?=?LoginService.getInstance();??
17. ??????
18. ????<span?style="color:#ff6666;">//外线程访问UI线程的Handle??
19. ????private?Handler?mhandle?=?new?Handler(){??
20. ????????@Override??
21. ????????public?void?handleMessage(Message?msg)?{??
22. ????????????Toast.makeText(BadCodeActivity.this,?"登录成功",?Toast.LENGTH_LONG).show();??
23. ????????}??
24. ????};</span>??
25. ??????
26. ??????
27. ????/**?Called?when?the?activity?is?first?created.?*/??
28. ????@Override??
29. ????public?void?onCreate(Bundle?savedInstanceState)?{??
30. ????????super.onCreate(savedInstanceState);??
31. ????????setContentView(R.layout.main);??
32. ??
33. ????????new?Thread(new?Runnable()?{??
34. ????????????@Override??
35. ????????????public?void?run()?{??
36. ????????????????while(!lService.isLogin()?)?{??
37. ????????????????????try?{??
38. ????????????????????????lService.login();??
39. ????????????????????????Thread.sleep(1000);??
40. ????????????????????}?catch?(InterruptedException?e)?{??
41. ????????????????????????e.printStackTrace();??
42. ????????????????????}??
43. ????????????????}??
44. ????????????????<span?style="color:#ff0000;">mhandle.sendEmptyMessage(0);</span>??
45. ????????????}??
46. ????????}).start();??
47. ????}??
48. }??

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1. <p><span?style="background-color:?rgb(255,?255,?255);">红色部分代码，就是修改的地方。现在，这段代码可以运行了，而且还貌似不错，是吧。</span></p><p><span?style="background-color:?rgb(255,?255,?255);">但是，一个好的程序，不能只是应付正常情况，还要应付错误情况，是吧。如果登录总是出错怎么样呢？我们把LoginService类略微改动，如下：</span></p>??

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[java]?view plaincopy

1. package?com.study;??
2. ??
3. import?android.util.Log;??
4. ??
5. /**?
6. ?*?虚拟的一个登录服务.?
7. ?*?@author?yihui823?
8. ?*/??
9. public?class?LoginService?{??
10. ??
11. ????private?static?final?String?TAG?=?"LoginService";??
12. ??????
13. ????//单例??
14. ????private?static?LoginService?oneInstance?=?new?LoginService();??
15. ??????
16. ????/**?
17. ?????*?得到唯一的一个单例?
18. ?????*?@return?唯一的一个单例?
19. ?????*/??
20. ????public?static?LoginService?getInstance()?{??
21. ????????return?oneInstance;??
22. ????}??
23. ??????
24. ????//登录成功标记??
25. ????private?boolean?hadLogin?=?false;??
26. ??????
27. ????/**?
28. ?????*?模拟登录操作?
29. ?????*?@return?true:登录成功?
30. ?????*/??
31. ????public?boolean?login()?{??
32. ????????try?{??
33. ????????????Thread.sleep(2000);??
34. ????????}?catch?(InterruptedException?e)?{??
35. ????????}??
36. ????????Log.d(TAG,?"we?are?login");??
37. //??????hadLogin?=?true;??
38. ??????????
39. ????????return?hadLogin;??
40. ????}??
41. ??????
42. ????/**?
43. ?????*?判断是否登录?
44. ?????*?@return?true:已经登录?
45. ?????*/??
46. ????public?boolean?isLogin()?{??
47. ????????return?hadLogin;??
48. ????}??
49. }??

增加了Log，以便查看登录情况。模拟业务代码只改了一行，就是登录永远是失败。现在运行一下呢。停在页面上没有动静了，logcat里也不断的打出：
we are login
这个也不会有什么错误，对吧。但是，我们如果按“返回”键退出页面，再看看logcat呢？
we are login的log还在不停的输出，是吗？
我想现在大家应该知道哪里出了问题了。就是说，我们的线程启动之后，就没法停掉了。
这里我要说一下。我一直认为，
new Thread(new Runnable() {…}().start();
这种代码写的非常的不好。你直接构造了一个对象，但是这个对象你没有任何的变量去指向它。这个线程被你启动之后，你已经无法再去跟踪、调用、管理了。这个线程，只能自生自灭，永远游离在你的控制范围之外。你会不会觉得，这个线程跟僵尸一样?对，这就是僵尸进程，如果它没有停止的条件，就永远在你的系统里消耗你的资源。
所以我觉得使用线程的一个基本认识：生成的线程类，一定要有一个变量去指向它，以便在合适的时候销毁。
这里说到销毁，这就是另一个问题了。Thread类已经废弃了stop方法了，因为线程需要自行去释放该释放的资源，不能光依赖于运行框架的控制。我们需要在Thread里面，加上他自己停止的代码。也就是说，不论如何，线程应该会自己去停止掉，而不应该是无限制的运行。
另外，我们在Android里面，还应该注意Activity的各个状态周转。一般来说，线程的启动在onCreate里是不合适的，我们必须考虑到onResume和onPause的情况。
那么，我们总结下，Activity里使用线程有三个注意：
1， 线程对象一定要有变量指向它，以便我们可以控制。
2， 线程类一定要有停止条件，以便外界通知线程自行停止。
3， 在onResume里启动线程，在onPause里停止线程。
我们根据以上三点，重新写一下Activity。

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[java]?view plaincopy

1. package?com.study;??
2. ??
3. import?android.app.Activity;??
4. import?android.os.Bundle;??
5. import?android.os.Handler;??
6. import?android.os.Message;??
7. import?android.util.Log;??
8. import?android.widget.Toast;??
9. ??
10. /**?
11. ?*?一个段不好的代码?
12. ?*?@author?yihui823?
13. ?*/??
14. public?class?BadCodeActivity?extends?Activity?{??
15. ??
16. ????private?static?final?String?TAG?=?"BadCodeActivity";??
17. ??????
18. ????//登录服务??
19. ????private?LoginService?lService?=?LoginService.getInstance();??
20. ??????
21. ????//外线程访问UI线程的Handle??
22. ????private?Handler?mhandle?=?new?Handler(){??
23. ????????@Override??
24. ????????public?void?handleMessage(Message?msg)?{??
25. ????????????Toast.makeText(BadCodeActivity.this,?"登录成功",?Toast.LENGTH_LONG).show();??
26. ????????}??
27. ????};??
28. ??????
29. ????//通知停止线程的标记??
30. ????private?boolean?stopFlag?=?false;??
31. ??????
32. ????//登录成功标记??
33. ????private?boolean?loginOk?=?false;??
34. ??????
35. ????/**?
36. ?????*?登录用的线程类?
37. ?????*/??
38. ????private?class?LoginThread?extends?Thread?{??
39. ??????????
40. ????????@Override??
41. ????????public?void?run()?{??
42. ????????????while(!stopFlag)?{??
43. ????????????????loginOk?=?lService.isLogin();??
44. ????????????????if?(loginOk)?{??
45. ????????????????????break;??
46. ????????????????}??
47. ????????????????try?{??
48. ????????????????????lService.login();??
49. ????????????????????Thread.sleep(1000);??
50. ????????????????}?catch?(InterruptedException?e)?{??
51. ????????????????????e.printStackTrace();??
52. ????????????????}??
53. ????????????}??
54. ????????????mhandle.sendEmptyMessage(0);??
55. ????????}??
56. ??????????
57. ????????/**?
58. ?????????*?通知线程需要停止?
59. ?????????*/??
60. ????????public?void?stopLogin()?{??
61. ????????????stopFlag?=?true;??
62. ????????}??
63. ????};??
64. ??
65. ????//用来登录的线程??
66. ????private?LoginThread?loginThread?=?new?LoginThread();??
67. ??????
68. ??????
69. ????/**?Called?when?the?activity?is?first?created.?*/??
70. ????@Override??
71. ????public?void?onCreate(Bundle?savedInstanceState)?{??
72. ????????super.onCreate(savedInstanceState);??
73. ????????setContentView(R.layout.main);??
74. ????????Log.d(TAG,?"BadCodeActivity?instance?is?called?onCreate?:"?+?this.hashCode());??
75. ????}??
76. ??????
77. ????public?void?onResume()?{??
78. ????????super.onResume();??
79. ????????Log.d(TAG,?"BadCodeActivity?instance?is?called?onResume?:"?+?this.hashCode());??
80. ????????loginThread.start();??
81. ????}??
82. ??????
83. ????public?void?onPause()?{??
84. ????????super.onPause();??
85. ????????loginThread.stopLogin();??
86. ????}??
87. }??

现在，我们的线程可以在页面退出的时候正常停止了。
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但是这段代码还是有问题的。我们仔细看看，线程在Activity构造的时候就已经创建了，然后在程序进到前台的时候启动，退到后台的时候停止。但是线程有这么一个特性：
一旦线程的run()函数运行结束了，这个线程就销毁了，不能再启动了。
现在我们的程序，在退出后将不可能再次显示，所以系统会马上回收掉Activity。如果我们的页面增加一个按钮，迁移到另一个页面，那么在那个页面返回的时候，就会有异常出现。我们修改一下代码来试试。
增加一个Activity:

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[java]?view plaincopy

1. package?com.study;??
2. ??
3. import?android.app.Activity;??
4. import?android.os.Bundle;??
5. ??
6. /**?
7. ?*?临时页面?
8. ?*?@author?yihui823?
9. ?*/??
10. public?class?TempActivity?extends?Activity?{??
11. ??
12. ????/**?Called?when?the?activity?is?first?created.?*/??
13. ????@Override??
14. ????public?void?onCreate(Bundle?savedInstanceState)?{??
15. ????????super.onCreate(savedInstanceState);??
16. ????????setContentView(R.layout.main);??
17. ????}??
18. }??

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1. <pre?class="java"?name="code"></pre>??
2. <p>别忘了修改AndroidManifest.xml，增加Activity的说明：</p>??
3. <p?align="left">?????????<activity?android:name=".TempActivity"<br>??
4. ??????????????????android:label="@string/app_name"/><br>??
5. </p>??
6. <p?align="left">修改BadCodeActivity：</p>??
7. <p><br>??
8. </p>??
9. <pre?class="java"?name="code">package?com.study;??
10. ??
11. import?android.app.Activity;??
12. import?android.content.Intent;??
13. import?android.os.Bundle;??
14. import?android.os.Handler;??
15. import?android.os.Message;??
16. import?android.util.Log;??
17. import?android.view.View;??
18. import?android.view.View.OnClickListener;??
19. import?android.widget.Button;??
20. import?android.widget.Toast;??
21. ??
22. /**?
23. ?*?一个段不好的代码?
24. ?*?@author?yihui823?
25. ?*/??
26. public?class?BadCodeActivity?extends?Activity?{??
27. ??
28. ????private?static?final?String?TAG?=?"BadCodeActivity";??
29. ??????
30. ????//登录服务??
31. ????private?LoginService?lService?=?LoginService.getInstance();??
32. ??????
33. ????//外线程访问UI线程的Handle??
34. ????private?Handler?mhandle?=?new?Handler(){??
35. ????????@Override??
36. ????????public?void?handleMessage(Message?msg)?{??
37. ????????????Toast.makeText(BadCodeActivity.this,?"登录成功",?Toast.LENGTH_LONG).show();??
38. ????????}??
39. ????};??
40. ??????
41. ????//通知停止线程的标记??
42. ????private?boolean?stopFlag?=?false;??
43. ??????
44. ????//登录成功标记??
45. ????private?boolean?loginOk?=?false;??
46. ??????
47. ????/**?
48. ?????*?登录用的线程类?
49. ?????*/??
50. ????private?class?LoginThread?extends?Thread?{??
51. ??????????
52. ????????@Override??
53. ????????public?void?run()?{??
54. ????????????while(!stopFlag)?{??
55. ????????????????loginOk?=?lService.isLogin();??
56. ????????????????if?(loginOk)?{??
57. ????????????????????break;??
58. ????????????????}??
59. ????????????????try?{??
60. ????????????????????lService.login();??
61. ????????????????????Thread.sleep(1000);??
62. ????????????????}?catch?(InterruptedException?e)?{??
63. ????????????????????e.printStackTrace();??
64. ????????????????}??
65. ????????????}??
66. ????????????mhandle.sendEmptyMessage(0);??
67. ????????}??
68. ??????????
69. ????????/**?
70. ?????????*?通知线程需要停止?
71. ?????????*/??
72. ????????public?void?stopLogin()?{??
73. ????????????stopFlag?=?true;??
74. ????????}??
75. ????};??
76. ??
77. ????//用来登录的线程??
78. ????private?LoginThread?loginThread?=?new?LoginThread();??
79. ??????
80. ??????
81. ????/**?Called?when?the?activity?is?first?created.?*/??
82. ????@Override??
83. ????public?void?onCreate(Bundle?savedInstanceState)?{??
84. ????????super.onCreate(savedInstanceState);??
85. ????????setContentView(R.layout.main);??
86. ??????????
87. ?<span?style="color:#ff0000;">???????Button?btn?=?(Button)findViewById(R.id.btn);??
88. ????????btn.setOnClickListener(new?OnClickListener()?{??
89. ????????????@Override??
90. ????????????public?void?onClick(View?arg0)?{??
91. ????????????????startActivity(new?Intent(BadCodeActivity.this,TempActivity.class));??
92. ????????????}??
93. ????????});</span>??
94. ??????????
95. ????????Log.d(TAG,?"BadCodeActivity?instance?is?called?onCreate?:"?+?this.hashCode());??
96. ????}??
97. ??????
98. ????public?void?onResume()?{??
99. ????????super.onResume();??
100. ????????Log.d(TAG,?"BadCodeActivity?instance?is?called?onResume?:"?+?this.hashCode());??
101. ????????loginThread.start();??
102. ????}??
103. ??????
104. ????public?void?onPause()?{??
105. ????????super.onPause();??
106. ????????loginThread.stopLogin();??
107. ????}??
108. }??
109. </pre>??
110. <p><br>??
111. </p>??
112. <p?align="left">?</p>??
113. <p>其实就是加了一个按钮，做一个页面迁移。别忘了在main.xml里面加上：</p>??
114. <pre?class="html"?name="code"><Button??
115. ????android:id="@+id/btn"????
116. ????android:layout_width="fill_parent"???
117. ????android:layout_height="wrap_content"???
118. ????android:text="@string/hello"??
119. ????/>??
120. </pre>??
121. <p><br>??
122. ?</p>??
123. <p>现在我们运行程序。运行之后，点击按钮，画面闪动一下说明是切换了页面。我们偷了个懒，两个Activity共用一个layout，所以页面没有任何变化。但是没关系，我们看log，we?are?login已经停止输出了。这个时候，我们再按返回键，应该是切换回BadCodeActivity。这个时候系统报错：</p>??
124. <p>java.lang.IllegalThreadStateException:?Thread?already?started.</p>??
125. <p>显然，就是说线程已经启动过了，不能再次被利用。</p>??
126. <p>我们对代码需要做一点点修改。当然，我们也顺手改掉一个BUG：在退出的时候还会报告登录成功。</p>??
127. <p>并且，我们把控制变量都放在内部类里，做到变量最小化生存空间。</p>??
128. <p>修改后如下：</p>??
129. <pre?class="java"?name="code">package?com.study;??
130. ??
131. import?android.app.Activity;??
132. import?android.content.Intent;??
133. import?android.os.Bundle;??
134. import?android.os.Handler;??
135. import?android.os.Message;??
136. import?android.util.Log;??
137. import?android.view.View;??
138. import?android.view.View.OnClickListener;??
139. import?android.widget.Button;??
140. import?android.widget.Toast;??
141. ??
142. /**?
143. ?*?一个段不好的代码?
144. ?*?@author?yihui823?
145. ?*/??
146. public?class?BadCodeActivity?extends?Activity?{??
147. ??
148. ????private?static?final?String?TAG?=?"BadCodeActivity";??
149. ??????
150. ????//登录服务??
151. ????private?LoginService?lService?=?LoginService.getInstance();??
152. ??????
153. ????//外线程访问UI线程的Handle??
154. ????private?Handler?mhandle?=?new?Handler(){??
155. ????????@Override??
156. ????????public?void?handleMessage(Message?msg)?{??
157. ????????????Toast.makeText(BadCodeActivity.this,?"登录成功",?Toast.LENGTH_LONG).show();??
158. ????????}??
159. ????};??
160. ??????
161. ????/**?
162. ?????*?登录用的线程类?
163. ?????*/??
164. ????private?class?LoginThread?extends?Thread?{??
165. ??
166. ????????//通知停止线程的标记??
167. ????????private?boolean?stopFlag?=?false;??
168. ??????????
169. ????????//登录成功标记??
170. ????????private?boolean?loginOk?=?false;??
171. ??????????
172. ????????@Override??
173. ????????public?void?run()?{??
174. ????????????while(!stopFlag)?{??
175. ????????????????loginOk?=?lService.isLogin();??
176. ????????????????if?(loginOk)?{??
177. ????????????????????break;??
178. ????????????????}??
179. ????????????????try?{??
180. ????????????????????lService.login();??
181. ????????????????????Thread.sleep(1000);??
182. ????????????????}?catch?(InterruptedException?e)?{??
183. ????????????????????e.printStackTrace();??
184. ????????????????}??
185. ????????????}??
186. ????????????if?(loginOk)?{??
187. ????????????????mhandle.sendEmptyMessage(0);??
188. ????????????}??
189. ????????}??
190. ??????????
191. ????????/**?
192. ?????????*?通知线程需要停止?
193. ?????????*/??
194. ????????public?void?stopLogin()?{??
195. ????????????stopFlag?=?true;??
196. ????????}??
197. ????};??
198. ??
199. ????//用来登录的线程??
200. ????private?LoginThread?loginThread;??
201. ??????
202. ??????
203. ????/**?Called?when?the?activity?is?first?created.?*/??
204. ????@Override??
205. ????public?void?onCreate(Bundle?savedInstanceState)?{??
206. ????????super.onCreate(savedInstanceState);??
207. ????????setContentView(R.layout.main);??
208. ??????????
209. ????????Button?btn?=?(Button)findViewById(R.id.btn);??
210. ????????btn.setOnClickListener(new?OnClickListener()?{??
211. ????????????@Override??
212. ????????????public?void?onClick(View?arg0)?{??
213. ????????????????startActivity(new?Intent(BadCodeActivity.this,TempActivity.class));??
214. ????????????}??
215. ????????});??
216. ??????????
217. ????????Log.d(TAG,?"BadCodeActivity?instance?is?called?onCreate?:"?+?this.hashCode());??
218. ????}??
219. ??????
220. ????public?void?onResume()?{??
221. ????????super.onResume();??
222. ????????Log.d(TAG,?"BadCodeActivity?instance?is?called?onResume?:"?+?this.hashCode());??
223. ????????<span?style="color:#ff0000;">loginThread?=?new?LoginThread();</span>??
224. ????????loginThread.start();??
225. ????}??
226. ??????
227. ????public?void?onPause()?{??
228. ????????super.onPause();??
229. ????????loginThread.stopLogin();??
230. ????}??
231. }??
232. ??
233. </pre>??
234. <p?align="left"><br>??
235. ?</p>??
236. <p>现在，我们点击按钮，进入到TempActivity的时候，登录log停止输出；然后按返回键，回到BadCodeActivity的时候，登录log又继续输出。程序基本完成，没有僵尸线程存在了。红色的那行代码是关键！</p>??
237. <p>我们总结一下：</p>??
238. <p><strong>1，?线程对象一定要有变量指向它，以便我们可以控制。</strong></p>??
239. <p><strong>2，?线程类一定要有停止条件，以便外界通知线程自行停止。</strong></p>??
240. <p><strong>3，?线程启动之后，不管是不是已经停止了，都是不能再次利用的。</strong></p>??
241. <p>4，??<strong>在onResume里新建和启动线程，在onPause里停止线程。</strong></p>??
242. <p>?</p>??
243. <p>?</p>??
244. <pre></pre>??
245. <pre></pre>??
246. <pre></pre>??
247. <pre></pre> ?

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