kezhenxu94 commented on a change in pull request #2930: One more time for
heigher performance
URL: https://github.com/apache/skywalking/pull/2930#discussion_r296583740
##########
File path:
apm-commons/apm-datacarrier/src/main/java/org/apache/skywalking/apm/commons/datacarrier/common/AtomicRangeInteger.java
##########
@@ -20,28 +20,32 @@
package org.apache.skywalking.apm.commons.datacarrier.common;
import java.io.Serializable;
-import java.util.concurrent.atomic.AtomicInteger;
+import java.util.concurrent.atomic.AtomicIntegerArray;
/**
- * Created by wusheng on 2016/10/25.
+ * Created by lkxiaolou
*/
public class AtomicRangeInteger extends Number implements Serializable {
private static final long serialVersionUID = -4099792402691141643L;
- private AtomicInteger value;
+ private AtomicIntegerArray values;
+
+ private static final int VALUE_OFFSET = 15;
+
private int startValue;
private int endValue;
public AtomicRangeInteger(int startValue, int maxValue) {
- this.value = new AtomicInteger(startValue);
+ this.values = new AtomicIntegerArray(31);
Review comment:
> * 12 bytes(in OS 64-bits) for the array ref
The memory address of the array reference isn't necessarily next to the 31
`int`s, the reference can be allocated at another memory block far away from
the 31 `int`s, so it's unnecessary to take it into consideration.
> 4 bytes(int) * 13(size)
I think you had missed the same thing as I had, see
https://github.com/apache/skywalking/pull/2930#discussion_r296446602
the key point is "The value may cached anywhere in one line,."
consider the cache line as a sliding window (of size 64 in 64-bits OS and
size 32 in 32-bits OS), we must ensure that no matter where the window slides
to, there must be only one `value` that will change in the window, and the
remainings are `placeholders` that are never modified, to ensure that the cache
line only contains our desired `value` that is changing.
```text
15 * 4 = 60
15 * 4 = 60
+-------------------------------------------------+
+----------------------------------------------------------+
| | (4 bytes) |
|
+-------------------------------------------------+ value
+----------------------------------------------------------+
+--------------------------------------------------------------------+
| |
+--------------------------------------------------------------------+
cache line(sliding window) 64
+---------------------------->
slide
```
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