lkxiaolou commented on a change in pull request #2930: One more time for
heigher performance
URL: https://github.com/apache/skywalking/pull/2930#discussion_r296447517
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File path:
apm-commons/apm-datacarrier/src/main/java/org/apache/skywalking/apm/commons/datacarrier/common/AtomicRangeInteger.java
##########
@@ -18,54 +18,108 @@
package org.apache.skywalking.apm.commons.datacarrier.common;
+import sun.misc.Unsafe;
-import java.io.Serializable;
-import java.util.concurrent.atomic.AtomicInteger;
+import java.lang.reflect.Field;
+import java.security.AccessController;
+import java.security.PrivilegedExceptionAction;
/**
- * Created by wusheng on 2016/10/25.
+ * @author lkxiaolou 2019-06-22
*/
-public class AtomicRangeInteger extends Number implements Serializable {
- private static final long serialVersionUID = -4099792402691141643L;
- private AtomicInteger value;
- private int startValue;
- private int endValue;
+public class AtomicRangeInteger extends Number implements java.io.Serializable
{
+
+ private static final long serialVersionUID = 4099792402691141643L;
+
+ private static final Unsafe UNSAFE;
+ private static final int SHIFT;
+ private static final int BASE;
+ private static final int VALUES_LENGTH = 31;
+ private static final int VALUES_OFFSET = 15;
+ private static final long VALUE_BYTE_OFFSET;
+
+ private volatile int[] values;
+ private final int startValue;
+ private final int endValue;
+
+ static {
+ try
+ {
+ final PrivilegedExceptionAction<Unsafe> action = new
PrivilegedExceptionAction<Unsafe>() {
+ @Override
+ public Unsafe run() throws Exception {
+ Field theUnsafe =
Unsafe.class.getDeclaredField("theUnsafe");
+ theUnsafe.setAccessible(true);
+ return (Unsafe) theUnsafe.get(null);
+ }
+ };
+
+ UNSAFE = AccessController.doPrivileged(action);
+ int scale = UNSAFE.arrayIndexScale(int[].class);
+ if ((scale & (scale - 1)) != 0) {
+ throw new Error("data type scale not a power of two");
+ }
+
+ SHIFT = 31 - Integer.numberOfLeadingZeros(scale);
+ BASE = UNSAFE.arrayBaseOffset(int[].class);
+
+ VALUE_BYTE_OFFSET = ((long) VALUES_OFFSET << SHIFT) + BASE;
+
+ } catch (Exception e) {
+ throw new RuntimeException("Unable to load unsafe", e);
+ }
+ }
public AtomicRangeInteger(int startValue, int maxValue) {
- this.value = new AtomicInteger(startValue);
+
+ this.values = new int[VALUES_LENGTH];
+ this.values[VALUES_OFFSET] = startValue;
+
this.startValue = startValue;
this.endValue = maxValue - 1;
}
public final int getAndIncrement() {
int next;
do {
- next = this.value.incrementAndGet();
- if (next > endValue && this.value.compareAndSet(next, startValue))
{
+ next = this.incrementAndGet();
+ if (next > endValue && this.compareAndSet(next, startValue)) {
return endValue;
}
} while (next > endValue);
return next - 1;
}
+ private final boolean compareAndSet(int expect, int update) {
+ return UNSAFE.compareAndSwapInt(values, VALUE_BYTE_OFFSET, expect,
update);
+ }
+
+ private final int incrementAndGet() {
+ return UNSAFE.getAndAddInt(values, VALUE_BYTE_OFFSET, 1) + 1;
+ }
+
public final int get() {
- return this.value.get();
+ return this.values[VALUES_OFFSET];
Review comment:
Current value has changed by the Unsafe native function, see compareAndSet
and incrementAndGet.
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