From 6f85f1f5477eb23ef87edb01dbcc422ca2f84f37 Mon Sep 17 00:00:00 2001
From: Uros Bojanic <157381213+uros-db@users.noreply.github.com>
Date: Fri, 28 Jun 2024 09:46:40 +0200
Subject: [PATCH 1/3] Initial commit

---
 .../org/apache/spark/unsafe/types/UTF8String.java    | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index 49d3088f8a2f0..4156287541252 100644
--- a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -23,6 +23,7 @@
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
 import java.util.Map;
 import java.util.regex.Pattern;
@@ -58,6 +59,7 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
   private Object base;
   private long offset;
   private int numBytes;
+  private AtomicInteger numChars = new AtomicInteger(0);
 
   public Object getBaseObject() { return base; }
   public long getBaseOffset() { return offset; }
@@ -253,6 +255,16 @@ public int numBytes() {
    * Returns the number of code points in it.
    */
   public int numChars() {
+    numChars.compareAndSet(0, getNumChars());
+    return numChars.get();
+  }
+
+  /**
+   * Private helper method to calculate the number of code points in the UTF-8 string. Counting
+   * the code points is a linear time operation, as we need to scan the entire UTF-8 string.
+   * Hence, this method should generally only be called once for non-empty UTF-8 strings.
+   */
+  private int getNumChars() {
     int len = 0;
     for (int i = 0; i < numBytes; i += numBytesForFirstByte(getByte(i))) {
       len += 1;

From 9fd254b839c522873c6e383adc801e35489f3850 Mon Sep 17 00:00:00 2001
From: Uros Bojanic <157381213+uros-db@users.noreply.github.com>
Date: Fri, 28 Jun 2024 09:52:17 +0200
Subject: [PATCH 2/3] Use -1 initially

---
 .../main/java/org/apache/spark/unsafe/types/UTF8String.java   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index 4156287541252..ec59a3248cb17 100644
--- a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -59,7 +59,7 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
   private Object base;
   private long offset;
   private int numBytes;
-  private AtomicInteger numChars = new AtomicInteger(0);
+  private AtomicInteger numChars = new AtomicInteger(-1);
 
   public Object getBaseObject() { return base; }
   public long getBaseOffset() { return offset; }
@@ -255,7 +255,7 @@ public int numBytes() {
    * Returns the number of code points in it.
    */
   public int numChars() {
-    numChars.compareAndSet(0, getNumChars());
+    numChars.compareAndSet(-1, getNumChars());
     return numChars.get();
   }
 

From 913b79a558a14e765f961e217fb4226954713142 Mon Sep 17 00:00:00 2001
From: Uros Bojanic <157381213+uros-db@users.noreply.github.com>
Date: Fri, 28 Jun 2024 14:10:25 +0200
Subject: [PATCH 3/3] Use volatile

---
 .../java/org/apache/spark/unsafe/types/UTF8String.java     | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
index ec59a3248cb17..b580f5fb4b4f6 100644
--- a/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
+++ b/common/unsafe/src/main/java/org/apache/spark/unsafe/types/UTF8String.java
@@ -23,7 +23,6 @@
 import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Function;
 import java.util.Map;
 import java.util.regex.Pattern;
@@ -59,7 +58,7 @@ public final class UTF8String implements Comparable<UTF8String>, Externalizable,
   private Object base;
   private long offset;
   private int numBytes;
-  private AtomicInteger numChars = new AtomicInteger(-1);
+  private volatile int numChars = -1;
 
   public Object getBaseObject() { return base; }
   public long getBaseOffset() { return offset; }
@@ -255,8 +254,8 @@ public int numBytes() {
    * Returns the number of code points in it.
    */
   public int numChars() {
-    numChars.compareAndSet(-1, getNumChars());
-    return numChars.get();
+    if (numChars == -1) numChars = getNumChars();
+    return numChars;
   }
 
   /**