Differences

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--- readers-writers [2007/10/05 12:14] – created franck
+++ readers-writers [2007/10/05 12:24] (current) – franck
@@ Line 5: / Line 5: @@
 <code java>
 /**
- * This class represents a database.  There are many competing
+  This class represents a database.  There are many
- * threads wishing to read and write.  It is acceptable to have
+  competing threads wishing to read and write.  It is
- * multiple processes reading at the same time, but if one thread
+  acceptable to have multiple processes reading at the
- * is writing then no other process may either read or write.
+  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
+  private int readers; // number of active readers
-    /**
+  /**
-       Initializes this database.
+    Initializes this database.
-    */
+  */
-    public Database()
+  public Database()
+  {
+    this.readers = 0;
+  }
+  /**
+    Read from this database.
+    @param number Number of the reader.
+  */
+  public void read(int number)
+  {
+    synchronized(this)
     {
-        this.readers = 0;
+      this.readers++;
+      System.out.println("Reader " + number + " starts reading.");
     }
-    /**
+    final int DELAY = 5000;
-       Read from this database.
+    try
-       @param number Number of the reader.
-    */
-    public void read(int number)
     {
-        synchronized(this)
+      Thread.sleep((int) (Math.random() * DELAY));
-        {
+    }
-            this.readers++;
+    catch (InterruptedException e) {}
-            System.out.println("Reader " + number + " starts reading.");
-        }
-        final int DELAY = 5000;
+    synchronized(this)
-        try
+    {
-        {
+      System.out.println("Reader " + number + " stops reading.");
-            Thread.sleep((int) (Math.random() * DELAY));
+      this.readers--;
-        }
+      if (this.readers == 0)
-        catch (InterruptedException e) {}
+      {
+        this.notifyAll();
-        synchronized(this)
+      }
-        {
-            System.out.println("Reader " + number + " stops reading.");
-            this.readers--;
-            if (this.readers == 0)
-            {
-                this.notifyAll();
-            }
-        }
     }
+  }
-    /**
+  /**
-       Writes to this database.
+    Writes to this database.
-       @param number Number of the writer.
+    @param number Number of the writer.
-    */
+  */
-    public synchronized void write(int number)
+  public synchronized void write(int number)
+  {
+    while (this.readers != 0)
     {
-        while (this.readers != 0)
+      try
-        {
+      {
-            try
+        this.wait();
-            {
+      }
-                this.wait();
+      catch (InterruptedException e) {}
-            }
+    }
-            catch (InterruptedException e) {}
+    System.out.println("Writer " + number + " starts writing.");
-        }
-        System.out.println("Writer " + number + " starts writing.");
-        final int DELAY = 5000;
-        try
-        {
-            Thread.sleep((int) (Math.random() * DELAY));
-        }
-        catch (InterruptedException e) {}
-        System.out.println("Writer " + number + " stops writing.");
+    final int DELAY = 5000;
-        this.notifyAll();
+    try
+    {
+      Thread.sleep((int) (Math.random() * DELAY));
     }
+    catch (InterruptedException e) {}
+    System.out.println("Writer " + number + " stops writing.");
+    this.notifyAll();
+ }
 }
 </code>
@@ Line 86: / Line 87: @@
 <code java>
+/**
+   This class represents a reader.
+*/
+public class Reader extends Thread
+{
+  private static int readers = 0; // number of readers
+  private int number;
+  private Database database;
+  /**
+    Creates a Reader for the specified database.
+    @param database database from which to be read.
+  */
+  public Reader(Database database)
+  {
+    this.database = database;
+    this.number = Reader.readers++;
+  }
+  /**
+    Reads.
+  */
+  public void run()
+  {
+    while (true)
+    {
+      final int DELAY = 5000;
+      try
+      {
+        Thread.sleep((int) (Math.random() * DELAY));
+      }
+      catch (InterruptedException e) {}
+      this.database.read(this.number);
+    }
+  }
+}
 </code>
@@ Line 92: / Line 130: @@
 <code java>
+/**
+  This class represents a writer.
+*/
+public class Writer extends Thread
+{
+  private static int writers = 0; // number of writers
+  private int number;
+  private Database database;
+  /**
+    Creates a Writer for the specified database.
+    @param database database to which to write.
+  */
+  public Writer(Database database)
+  {
+    this.database = database;
+    this.number = Writer.writers++;
+  }
+  /**
+    Writes.
+  */
+  public void run()
+  {
+    while (true)
+    {
+      final int DELAY = 5000;
+      try
+      {
+        Thread.sleep((int) (Math.random() * DELAY));
+      }
+      catch (InterruptedException e) {}
+      this.database.write(this.number);
+    }
+  }
+}
 </code>
@@ Line 98: / Line 173: @@
 <code java>
+/**
+  This app creates a specified number of readers and
+  writers and starts them.
+*/
+public class Simulator
+{
+  /**
+    Creates the specified number of readers and writers and starts them.
+    @param args[0] The number of readers.
+    @param args[1] The number of writers.
+  */
+  public static void main(String[] args)
+  {
+    if (args.length < 2)
+    {
+      System.out.println("Usage: java Simulator <number of readers> <number of writers>");
+    }
+    else
+    {
+      final int READERS = Integer.parseInt(args[0]);
+      final int WRITERS = Integer.parseInt(args[1]);
+      Database database = new Database();
+      for (int i = 0; i < READERS; i++)
+      {
+        new Reader(database).start();
+      }
+      for (int i = 0; i < WRITERS; i++)
+      {
+        new Writer(database).start();
+      }
+    }
+  }
+}
 </code>