Author: rjung
Date: Fri Oct 29 17:41:05 2010
New Revision: 1028861
URL: http://svn.apache.org/viewvc?rev=1028861&view=rev
Log:
Improve Jsp limiter:
- Under high load entries removed from the jspQueue
were already re-added via moveFirst by some other
concurrent request, before the JspWrapper was
unregistered. Add "valid" field to the Entry
object to mark as invalid during removal.
- Improve comment about thread-safetyness and add
comment about the new "valid" field.
- Add new getSize(). Will be used soon.
- Reorder getters and setters of Entry.
Modified:
tomcat/trunk/java/org/apache/jasper/util/FastRemovalDequeue.java
Modified: tomcat/trunk/java/org/apache/jasper/util/FastRemovalDequeue.java
URL:
http://svn.apache.org/viewvc/tomcat/trunk/java/org/apache/jasper/util/FastRemovalDequeue.java?rev=1028861&r1=1028860&r2=1028861&view=diff
==============================================================================
--- tomcat/trunk/java/org/apache/jasper/util/FastRemovalDequeue.java (original)
+++ tomcat/trunk/java/org/apache/jasper/util/FastRemovalDequeue.java Fri Oct 29
17:41:05 2010
@@ -29,6 +29,11 @@ package org.apache.jasper.util;
* linked list, so that removal of an Entry does not need to search for it but
* instead can be done in constant time.
*
+ * The implementation is not thread-safe. Full synchronisation has to be
provided
+ * externally. Invalidation of Entry objects during removal from the list is
done
+ * by setting their valid field to false. All public methods which take Entry
+ * objects as arguments are NOP if the entry is no longer valid.
+ *
* A typical use of the FastRemovalDequeue is a list of entries in sorted
order,
* where the sort position of an object will only switch to first or last.
*
@@ -43,11 +48,25 @@ public class FastRemovalDequeue<T> {
private Entry first;
/** Last element of the queue. */
private Entry last;
+ /** Size of the queue */
+ private int size;
/** Initialize empty queue. */
public FastRemovalDequeue() {
first = null;
last = null;
+ size = 0;
+ }
+
+ /**
+ * Retrieve the size of the list.
+ * This method also needs to be externaly synchronized to
+ * ensure correct publication of changes.
+ *
+ * @return the size of the list.
+ * */
+ public int getSize() {
+ return size;
}
/**
@@ -66,6 +85,7 @@ public class FastRemovalDequeue<T> {
entry.setNext(first);
first = entry;
}
+ size++;
return entry;
}
@@ -86,6 +106,7 @@ public class FastRemovalDequeue<T> {
entry.setPrevious(last);
last = entry;
}
+ size++;
return entry;
}
@@ -99,10 +120,12 @@ public class FastRemovalDequeue<T> {
T content = null;
if (first != null) {
content = first.getContent();
+ first.setValid(false);
first = first.getNext();
if (first != null) {
first.setPrevious(null);
}
+ size--;
}
return content;
}
@@ -116,10 +139,12 @@ public class FastRemovalDequeue<T> {
T content = null;
if (last != null) {
content = last.getContent();
+ last.setValid(false);
last = last.getPrevious();
if (last != null) {
last.setNext(null);
}
+ size--;
}
return content;
}
@@ -128,6 +153,9 @@ public class FastRemovalDequeue<T> {
* Removes any element of the list and returns its content.
**/
public void remove(final Entry element) {
+ if (!element.getValid()) {
+ return;
+ }
Entry next = element.getNext();
Entry prev = element.getPrevious();
if (next != null) {
@@ -140,6 +168,7 @@ public class FastRemovalDequeue<T> {
} else {
first = next;
}
+ size--;
}
/**
@@ -151,7 +180,8 @@ public class FastRemovalDequeue<T> {
* @param element the entry to move in front.
* */
public void moveFirst(final Entry element) {
- if (element.getPrevious() != null) {
+ if (element.getValid() &&
+ element.getPrevious() != null) {
Entry prev = element.getPrevious();
Entry next = element.getNext();
prev.setNext(next);
@@ -176,7 +206,8 @@ public class FastRemovalDequeue<T> {
* @param element the entry to move to the back.
* */
public void moveLast(final Entry element) {
- if (element.getNext() != null) {
+ if (element.getValid() &&
+ element.getNext() != null) {
Entry next = element.getNext();
Entry prev = element.getPrevious();
next.setPrevious(prev);
@@ -200,35 +231,45 @@ public class FastRemovalDequeue<T> {
*/
public class Entry {
+ /** Is this entry still valid? */
+ private boolean valid = true;
/** The content this entry is valid for. */
private final T content;
/** Pointer to next element in queue. */
- private Entry next;
+ private Entry next = null;
/** Pointer to previous element in queue. */
- private Entry previous;
+ private Entry previous = null;
private Entry(T object) {
content = object;
}
- private final void setNext(final Entry next) {
- this.next = next;
+ private final boolean getValid() {
+ return valid;
}
- private final void setPrevious(final Entry previous) {
- this.previous = previous;
+ private final void setValid(final boolean valid) {
+ this.valid = valid;
}
private final T getContent() {
return content;
}
+ private final Entry getNext() {
+ return next;
+ }
+
+ private final void setNext(final Entry next) {
+ this.next = next;
+ }
+
private final Entry getPrevious() {
return previous;
}
- private final Entry getNext() {
- return next;
+ private final void setPrevious(final Entry previous) {
+ this.previous = previous;
}
@Override
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