SFib


1   import EDU.oswego.cs.dl.util.concurrent.*;
2   import java.net.*;
3   import java.io.*;
4   
5   /**
6    * Recursive task-based version of Fibonacci. Computes:
7    * <pre>
8    * Computes fibonacci(n) = fibonacci(n-1) + fibonacci(n-2);  for n> 1
9    *          fibonacci(0) = 0; 
10   *          fibonacci(1) = 1.       
11   * </pre>
12   **/
13  
14  public class SFib extends FJTask {
15  
16    // Performance-tuning constant:
17    static int sequentialThreshold = 0;
18    
19    public static void main(String  [] args) {
20      try {
21        int procs;
22        //      int num;
23        try {
24          procs = Integer.parseInt(args[0]);
25          //        num = Integer.parseInt(args[1]);
26          if (args.length > 2) sequentialThreshold = Integer.parseInt(args[2]);
27        }
28        catch (Exception   e) {
29          System.out.println("Usage: java SFib <threads> <number> [<sequntialThreshold>]");
30          return;
31        }
32  
33        FJTaskRunnerGroup group = new FJTaskRunnerGroup(procs);
34        ServerSocket socket = new ServerSocket(1618);
35        for (;;) {
36           final Socket connection = socket.accept();
37           group.execute(new Handler(connection));
38        }
39  
40      }
41      catch (Exception   e) { e.printStackTrace(); }
42    }
43  
44    static class Handler extends FJTask {
45      final Socket s;
46      Handler(Socket s) { this.s = s; }
47      public void run() { 
48        try {
49          DataInputStream i = new DataInputStream(s.getInputStream());
50          DataOutputStream o = new DataOutputStream(s.getOutputStream());
51          int n = i.readInt();
52          SFib f = new SFib(n);
53          invoke(f);
54          o.writeInt(f.getAnswer());
55        }
56        catch (Exception   e) { e.printStackTrace(); }
57      }
58    }
59  
60  
61    // Initialized with argument; replaced with result
62    volatile int number;
63  
64    SFib(int n) { number = n; }
65  
66    int getAnswer() {
67      if (!isDone()) throw new Error  ("Not yet computed");
68      return number;
69    }
70  
71  
72    public void run() {
73      int n = number;
74  
75      // Handle base cases:
76      if (n <= 1) {
77        // Do nothing: fib(0) = 0; fib(1) = 1
78      }
79      // Use sequential code for small problems:
80      else if (n <= sequentialThreshold) {
81        number = seqFib(n);
82      }
83      // Otherwise use recursive parallel decomposition:
84      else {
85        // Construct subtasks:
86        SFib f1 = new SFib(n - 1);
87        SFib f2 = new SFib(n - 2);
88        
89        // Run them in parallel:
90        coInvoke(f1, f2);  
91        
92        // Combine results:
93        number = f1.number + f2.number;
94        // (We know numbers are ready, so directly access them.)
95      }
96    }
97  
98    // Sequential version for arguments less than threshold
99    static int seqFib(int n) {
100     if (n <= 1) 
101       return n;
102     else 
103       return seqFib(n-1) + seqFib(n-2);
104   }
105 
106 }
107 
108
A to Z: JavaDoc & Examples Daily Java News & Articles Open Source Projects Open Source Codes Free Computer Books Remove Frame
Free Books Free Magazines
Popular Tags