libjava/classpath/java/util/logging/MemoryHandler.java

/* MemoryHandler.java -- a class for buffering log messages in a memory buffer
   Copyright (C) 2002, 2004 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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02110-1301 USA.

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permission to link this library with independent modules to produce an
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package java.util.logging;

/**
 * A <code>MemoryHandler</code> maintains a circular buffer of
 * log records.
 *
 * <p><strong>Configuration:</strong> Values of the subsequent
 * <code>LogManager</code> properties are taken into consideration
 * when a <code>MemoryHandler</code> is initialized.
 * If a property is not defined, or if it has an invalid
 * value, a default is taken without an exception being thrown.
 *
 * <ul>
 * <li><code>java.util.MemoryHandler.level</code> - specifies
 *     the initial severity level threshold. Default value:
 *     <code>Level.ALL</code>.</li>
 * <li><code>java.util.MemoryHandler.filter</code> - specifies
 *     the name of a Filter class. Default value: No Filter.</li>
 * <li><code>java.util.MemoryHandler.size</code> - specifies the
 *     maximum number of log records that are kept in the circular
 *     buffer.  Default value: 1000.</li>
 * <li><code>java.util.MemoryHandler.push</code> - specifies the
 *     <code>pushLevel</code>. Default value:
 *     <code>Level.SEVERE</code>.</li>
 * <li><code>java.util.MemoryHandler.target</code> - specifies the
 *     name of a subclass of {@link Handler} that will be used as the
 *     target handler.  There is no default value for this property;
 *     if it is not set, the no-argument MemoryHandler constructor
 *     will throw an exception.</li>
 * </ul>
 *
 * @author Sascha Brawer (brawer@acm.org)
 */
public class MemoryHandler
  extends Handler
{
  /**
   * The storage area used for buffering the unpushed log records in
   * memory.
   */
  private final LogRecord[] buffer;


  /**
   * The current position in the circular buffer. For a new
   * MemoryHandler, or immediately after {@link #push()} was called,
   * the value of this variable is zero.  Each call to {@link
   * #publish(LogRecord)} will store the published LogRecord into
   * <code>buffer[position]</code> before position is incremented by
   * one.  If position becomes greater than the size of the buffer, it
   * is reset to zero.
   */
  private int position;


  /**
   * The number of log records which have been published, but not
   * pushed yet to the target handler.
   */
  private int numPublished;


  /**
   * The push level threshold for this <code>Handler</code>.  When a
   * record is published whose severity level is greater than or equal
   * to the <code>pushLevel</code> of this <code>MemoryHandler</code>,
   * the {@link #push()} method will be invoked for pushing the buffer
   * contents to the target <code>Handler</code>.
   */
  private Level pushLevel;


  /**
   * The Handler to which log records are forwarded for actual
   * publication.
   */
  private final Handler target;


  /**
   * Constructs a <code>MemoryHandler</code> for keeping a circular
   * buffer of LogRecords; the initial configuration is determined by
   * the <code>LogManager</code> properties described above.
   */
  public MemoryHandler()
  {
    this((Handler) LogManager.getInstanceProperty(
           "java.util.logging.MemoryHandler.target",
           Handler.class, /* default */ null),
         LogManager.getIntPropertyClamped(
           "java.util.logging.MemoryHandler.size",
           /* default */ 1000,
           /* minimum value */ 1,
           /* maximum value */ Integer.MAX_VALUE),
         LogManager.getLevelProperty(
           "java.util.logging.MemoryHandler.push",
           /* default push level */ Level.SEVERE));
  }


  /**
   * Constructs a <code>MemoryHandler</code> for keeping a circular
   * buffer of LogRecords, given some parameters. The values of the
   * other parameters are taken from LogManager properties, as
   * described above.
   *
   * @param target the target handler that will receive those
   *               log records that are passed on for publication.
   *
   * @param size the number of log records that are kept in the buffer.
   *             The value must be a at least one.
   *
   * @param pushLevel the push level threshold for this
   *     <code>MemoryHandler</code>.  When a record is published whose
   *     severity level is greater than or equal to
   *     <code>pushLevel</code>, the {@link #push()} method will be
   *     invoked in order to push the bufffer contents to
   *     <code>target</code>.
   *
   * @throws java.lang.IllegalArgumentException if <code>size</code>
   *         is negative or zero. The GNU implementation also throws
   *         an IllegalArgumentException if <code>target</code> or
   *         <code>pushLevel</code> are <code>null</code>, but the
   *         API specification does not prescribe what should happen
   *         in those cases.
   */
  public MemoryHandler(Handler target, int size, Level pushLevel)
  {
    if ((target == null) || (size <= 0) || (pushLevel == null))
      throw new IllegalArgumentException();

    buffer = new LogRecord[size];
    this.pushLevel = pushLevel;
    this.target = target;

    setLevel(LogManager.getLevelProperty(
      "java.util.logging.MemoryHandler.level",
      /* default value */ Level.ALL));

    setFilter((Filter) LogManager.getInstanceProperty(
      "java.util.logging.MemoryHandler.filter",
      /* must be instance of */ Filter.class,
      /* default value */ null));
  }


  /**
   * Stores a <code>LogRecord</code> in a fixed-size circular buffer,
   * provided the record passes all tests for being loggable.  If the
   * buffer is full, the oldest record will be discarded.
   *
   * <p>If the record has a severity level which is greater than or
   * equal to the <code>pushLevel</code> of this
   * <code>MemoryHandler</code>, the {@link #push()} method will be
   * invoked for pushing the buffer contents to the target
   * <code>Handler</code>.
   *
   * <p>Most applications do not need to call this method directly.
   * Instead, they will use use a {@link Logger}, which will create
   * LogRecords and distribute them to registered handlers.
   *
   * @param record the log event to be published.
   */
  public void publish(LogRecord record)
  {
    if (!isLoggable(record))
      return;

    buffer[position] = record;
    position = (position + 1) % buffer.length;
    numPublished = numPublished + 1;

    if (record.getLevel().intValue() >= pushLevel.intValue())
      push();
  }


  /**
   * Pushes the contents of the memory buffer to the target
   * <code>Handler</code> and clears the buffer. Note that
   * the target handler will discard those records that do
   * not satisfy its own severity level threshold, or that are
   * not considered loggable by an installed {@link Filter}.
   *
   * <p>In case of an I/O failure, the {@link ErrorManager} of the
   * target <code>Handler</code> will be notified, but the caller of
   * this method will not receive an exception.
   */
  public void push()
  {
    int i;

    if (numPublished < buffer.length)
    {
      for (i = 0; i < position; i++)
        target.publish(buffer[i]);
    }
    else
    {
      for (i = position; i < buffer.length; i++)
        target.publish(buffer[i]);
      for (i = 0; i < position; i++)
        target.publish(buffer[i]);
    }

    numPublished = 0;
    position = 0;
  }


  /**
   * Forces any data that may have been buffered by the target
   * <code>Handler</code> to the underlying output device, but
   * does <em>not</em> push the contents of the circular memory
   * buffer to the target handler.
   *
   * <p>In case of an I/O failure, the {@link ErrorManager} of the
   * target <code>Handler</code> will be notified, but the caller of
   * this method will not receive an exception.
   *
   * @see #push()
   */
  public void flush()
  {
    target.flush();
  }


  /**
   * Closes this <code>MemoryHandler</code> and its associated target
   * handler, discarding the contents of the memory buffer.  However,
   * any data that may have been buffered by the target
   * <code>Handler</code> is forced to the underlying output device.
   *
   * <p>As soon as <code>close</code> has been called,
   * a <code>Handler</code> should not be used anymore. Attempts
   * to publish log records, to flush buffers, or to modify the
   * <code>Handler</code> in any other way may throw runtime
   * exceptions after calling <code>close</code>.</p>
   *
   * <p>In case of an I/O failure, the <code>ErrorManager</code> of
   * the associated target <code>Handler</code> will be informed, but
   * the caller of this method will not receive an exception.</p>
   *
   * @throws SecurityException if a security manager exists and
   *         the caller is not granted the permission to control
   *         the logging infrastructure.
   *
   * @see #push()
   */
  public void close()
    throws SecurityException
  {
    push();

    /* This will check for LoggingPermission("control"). If the
     * current security context does not grant this permission,
     * push() has been executed, but this does not impose a
     * security risk.
     */
    target.close();
  }



  /**
   * Returns the push level threshold for this <code>Handler</code>.
   * When a record is published whose severity level is greater
   * than or equal to the <code>pushLevel</code> of this
   * <code>MemoryHandler</code>, the {@link #push()} method will be
   * invoked for pushing the buffer contents to the target
   * <code>Handler</code>.
   *
   * @return the push level threshold for automatic pushing.
   */
  public Level getPushLevel()
  {
    return pushLevel;
  }


  /**
   * Sets the push level threshold for this <code>Handler</code>.
   * When a record is published whose severity level is greater
   * than or equal to the <code>pushLevel</code> of this
   * <code>MemoryHandler</code>, the {@link #push()} method will be
   * invoked for pushing the buffer contents to the target
   * <code>Handler</code>.
   *
   * @param pushLevel the push level threshold for automatic pushing.
   *
   * @exception SecurityException if a security manager exists and
   *            the caller is not granted the permission to control
   *            the logging infrastructure.
   *
   * @exception NullPointerException if <code>pushLevel</code> is
   *            <code>null</code>.
   */
  public void setPushLevel(Level pushLevel)
  {
    LogManager.getLogManager().checkAccess();

    /* Throws a NullPointerException if pushLevel is null. */
    pushLevel.getClass();

    this.pushLevel = pushLevel;
  }
}