用Java實現的第二類讀者寫者問題

用Java實現的第二類讀者寫者問題:

1. //--Semaphore.java</PRE><PRE class=java name="code">package rw;
3. public class Semaphore {
4. private int value;//記錄希望訪問臨界資源的線程的計數器個數
6. public Semaphore(int i)
7. {
8. this.value=i;
9. }
11. public synchronized void P()
12. {
13. value--;
14. if(value<0)
15. try {
16. wait();
17. } catch (InterruptedException e) {
18. e.printStackTrace();
19. Thread.currentThread().interrupt();
20. }
21. }
23. public synchronized void V()
24. {
25. value++;
26. if(value<=0)
27. {
28. notifyAll();
29. }
30. }
31. }</PRE><BR>
32. <PRE class=java name="code">//------------------------------文件2 ReaderWriter.java------------------------------------------------
33. package rw;
35. import java.io.FileNotFoundException;
36. import java.io.PrintStream;
38. public class ReaderWriter extends Thread{
40. String msg;
41. int NO;
42. final int N=100;
43. static public int num=0;
44. static public int readers=0;
45. static public int writers=0;
46. final static public String base="Last Writer:";
47. static public String resource=base+"0";
48. static Semaphore mutexr=new Semaphore(1);
49. static Semaphore mutexw=new Semaphore(1);
51. static Semaphore mutex=new Semaphore(1);
53. static Semaphore mutexWrite=new Semaphore(1);
55. public ReaderWriter()
56. {
57. NO=num++;
58. if(NO%N!=1)
59. msg="I am reader @"+NO;
60. else
61. msg="I am writer @"+NO;
62. }
64. public void read()
65. {
66. if(writers!=0)//如果有寫者，阻塞，並且後續的讀者不許進來
67. mutex.P();
68. mutexr.P();
69. readers++;
70. if(readers==1)//保證當讀的時候，對寫互斥，寫者等待
71. mutexWrite.P();
72. mutexr.V();
74. //.............................................讀開始...
75. System.out.println(" "+NO+" is reading, resource=" +resource);
76. //.............................................讀結束...
78. mutexr.P();
79. readers--;
80. if(readers==0)
81. mutexWrite.V();
82. mutexr.V();
83. if(writers!=0)//如果有寫者，阻塞，並且後續的讀者不許進來
84. mutex.V();
85. }
87. public void write()
88. {
90. mutexw.P();
91. writers++;
92. if(writers==1)
93. mutex.P();
94. mutexw.V();
96. //.....................................................寫開始
97. mutexWrite.P();
98. resource="base"+NO;
99. System.out.println(NO+" IS WRITING, resource=" +resource);
100. mutexWrite.V();
101. //.....................................................寫結束
103. mutexw.P();
104. writers--;
105. if(writers==0)
106. mutex.V();
107. mutexw.V();
108. }
110. public void run()
111. {
112. int n=1000;
113. while(n-->0)
114. {
115. if(NO%N!=1)
116. {/*
117. try {
118. Thread.sleep(1);
119. } catch (InterruptedException e) {
120. // TODO Auto-generated catch block
121. e.printStackTrace();
122. }
123. */
124. read();
125. }
126. else
127. {
128. write();
129. /*
130. try {
131. Thread.sleep(100);
132. } catch (InterruptedException e) {
133. // TODO Auto-generated catch block
134. e.printStackTrace();
135. }
136. */
137. }
138. }
139. }
141. public static void main(String args[])
142. {
143. PrintStream ps;
144. try {
145. ps = new PrintStream("D:\\readerWriter.txt");
146. System.setOut(ps);
147. } catch (FileNotFoundException e) {
148. e.printStackTrace();
149. }
150. for(int i=0;i<1000;i++)
151. {
152. new ReaderWriter().start();
153. }
154. }
155. }