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--- calendar [2009/04/26 19:40] – franck
+++ calendar [2009/05/14 21:04] (current) – franck
@@ Line 85: / Line 85: @@
 ===== March 31 =====
-A solution to the readers-writers problem using semaphores in Java.
+Implementations in Java of the reader-writers problem can be
-First, a Reader.
+found [[readers-writers|here]].
-<code java>
-package semaphore;
-import java.util.Random;
-import java.util.concurrent.Semaphore;
-/**
- * A reader.
- *
- * @author Franck van Breugel
- */
-public class Reader extends Thread
-{
-  private static int readers = 0;
-  private static final Semaphore mutex = new Semaphore(1);
-  /**
-   * Initializes this reader.
-   */
-  public Reader()
-  {
-    super();
-  }
-  /**
-   * Reads.
-   */
-  public void run()
-  {
-    try
-    {
-      Reader.mutex.acquire();
-      Reader.readers++;
-      if (Reader.readers == 1)
-      {
-        Writer.writer.acquire();
-      }
-      Reader.mutex.release();
-      // read
-      Reader.mutex.acquire();
-      Reader.readers--;
-      if (Reader.readers == 0)
-      {
-        Writer.writer.release();
-      }
-      Reader.mutex.release();
-    }
-    catch (InterruptedException e) {}
-  }
-}
-</code>
-Then, a Writer.
-<code java>
-package semaphore;
-import java.util.Random;
-import java.util.concurrent.Semaphore;
-/**
- * A writer.
- *
- * @author Franck van Breugel
- */
-public class Writer extends Thread
-{
-  public static final Semaphore writer = new Semaphore(1, true);
-  /**
-   * Initializes this writer.
-   */
-  public Writer()
-  {
-    super();
-  }
-  /**
-   * Writes.
-   */
-  public void run()
-  {
-    try
-    {
-      Writer.writer.acquire();
-      // write
-      Writer.writer.release();
-    }
-    catch (InterruptedException e) {}
-  }
-}
-</code>
-And finally an app.
-<code java>
-package semaphore;
-/**
- * This app creates a number of readers and writers.
- *
- * @author Franck van Breugel
- */
-public class ReadersWriters
-{
-  /**
-   * @param args[0] numbers of readers.
-   * @param args[1] number of writers.
-   */
-  public static void main(String[] args)
-  {
-    try
-    {
-      int readers = Integer.parseInt(args[0]);
-      int writers = Integer.parseInt(args[1]);
-      for (int i = 0; i < writers; i++)
-      {
-        new Writer().start();
-      }
-      for (int i = 0; i < readers; i++)
-      {
-        new Reader().start();
-      }
-    }
-    catch (Exception e)
-    {
-      System.out.println("Usage: java ReadersWriters < number of readers> <number of writers>");
-    }
-  }
-}
-</code>
-Below, we present another solution to the readers-writers problem.
-<code java>
-/**
- * This class represents a database.  There are many
- * competing threads wishing to read and write.  It is
- * acceptable to have multiple processes reading at the
- * same time, but if one thread is writing then no other
- * process may either read or write.
- */
-public class Database
-{
-  private int readers; // number of active readers
-  /**
-   * Initializes this database.
-   */
-  public Database()
-  {
-    this.readers = 0;
-  }
-  /**
-   * Read from this database.
-   */
-  public void read(int number)
-  {
-    synchronized(this)
-    {
-      this.readers++;
-    }
-    // read
-    synchronized(this)
-    {
-      this.readers--;
-      if (this.readers == 0)
-      {
-        this.notifyAll();
-      }
-    }
-  }
-  /**
-   * Writes to this database.
-   */
-  public synchronized void write(int number)
-  {
-    while (this.readers != 0)
-    {
-      try
-      {
-        this.wait();
-      }
-      catch (InterruptedException e) {}
-    }
-    // write
-    this.notifyAll();
-  }
-}
-</code>
 ===== April 2 =====
@@ Line 331: / Line 144: @@
 Willem Visser, Klaus Havelund, Guillaume Brat, SeungJoon Park and Flavio Lerda. [[http://dx.doi.org/10.1023/A:1022920129859|Model Checking Programs]]. //Automated Software Engineering//, 10(2): 203-232, April 2003.
-More information about Java PathFinder can be found
-[[jpf:start|here]].
 ===== May 7 =====
+More information about Java PathFinder can be found
+[[jpf:start|here]].
 ===== May 12 =====
+Information about handling native code with Java PathFinder can be found
+[[jpf-native:start|here]].
 ===== May 14 =====