java/src/org/apache/log4j/helpers/CyclicBuffer.java

@@ -0,0 +1,159 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ * 
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ * 
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+     
+package org.apache.log4j.helpers;
+
+import org.apache.log4j.spi.LoggingEvent;
+
+/**
+
+   CyclicBuffer is used by other appenders to hold {@link LoggingEvent
+   LoggingEvents} for immediate or differed display.
+   
+   <p>This buffer gives read access to any element in the buffer not
+   just the first or last element.
+
+   @author Ceki G&uuml;lc&uuml;
+   @since 0.9.0
+
+ */
+public class CyclicBuffer {
+  
+  LoggingEvent[] ea;
+  int first; 
+  int last; 
+  int numElems;
+  int maxSize;
+
+  /**
+     Instantiate a new CyclicBuffer of at most <code>maxSize</code> events.
+
+     The <code>maxSize</code> argument must a positive integer.
+
+     @param maxSize The maximum number of elements in the buffer.
+  */
+  public CyclicBuffer(int maxSize) throws IllegalArgumentException {
+    if(maxSize < 1) {
+      throw new IllegalArgumentException("The maxSize argument ("+maxSize+
+			    ") is not a positive integer.");
+    }
+    this.maxSize = maxSize;
+    ea = new LoggingEvent[maxSize];
+    first = 0;
+    last = 0;
+    numElems = 0;
+  }
+    
+  /**
+     Add an <code>event</code> as the last event in the buffer.
+
+   */
+  public
+  void add(LoggingEvent event) {    
+    ea[last] = event;    
+    if(++last == maxSize)
+      last = 0;
+
+    if(numElems < maxSize)
+      numElems++;
+    else if(++first == maxSize)
+      first = 0;
+  }
+
+
+  /**
+     Get the <i>i</i>th oldest event currently in the buffer. If
+     <em>i</em> is outside the range 0 to the number of elements
+     currently in the buffer, then <code>null</code> is returned.
+
+
+  */
+  public
+  LoggingEvent get(int i) {
+    if(i < 0 || i >= numElems)
+      return null;
+
+    return ea[(first + i) % maxSize];
+  }
+
+  public 
+  int getMaxSize() {
+    return maxSize;
+  }
+
+  /**
+     Get the oldest (first) element in the buffer. The oldest element
+     is removed from the buffer.
+  */
+  public
+  LoggingEvent get() {
+    LoggingEvent r = null;
+    if(numElems > 0) {
+      numElems--;
+      r = ea[first];
+      ea[first] = null;
+      if(++first == maxSize)
+	first = 0;
+    } 
+    return r;
+  }
+  
+  /**
+     Get the number of elements in the buffer. This number is
+     guaranteed to be in the range 0 to <code>maxSize</code>
+     (inclusive).
+  */
+  public
+  int length() {
+    return numElems;
+  } 
+
+  /**
+     Resize the cyclic buffer to <code>newSize</code>.
+
+     @throws IllegalArgumentException if <code>newSize</code> is negative.
+   */
+  public 
+  void resize(int newSize) {
+    if(newSize < 0) {
+      throw new IllegalArgumentException("Negative array size ["+newSize+
+					 "] not allowed.");
+    }
+    if(newSize == numElems)
+      return; // nothing to do
+    
+    LoggingEvent[] temp = new  LoggingEvent[newSize];
+
+    int loopLen = newSize < numElems ? newSize : numElems;
+    
+    for(int i = 0; i < loopLen; i++) {
+      temp[i] = ea[first];
+      ea[first] = null;
+      if(++first == numElems) 
+	first = 0;
+    }
+    ea = temp;
+    first = 0;
+    numElems = loopLen;
+    maxSize = newSize;
+    if (loopLen == newSize) {
+      last = 0;
+    } else {
+      last = loopLen;
+    }
+  }
+}