refactor: use computeIfAbsent for pattern cache lookup

Atomic and shorter. Avoids two threads compiling the same pattern under
contention.

Author: andygrove

common/src/main/scala/org/apache/comet/udf/RegExpExtractAllUDF.scala

@@ -59,15 +59,7 @@ class RegExpExtractAllUDF extends CometUDF {
       "RegExpExtractAllUDF requires a non-null scalar group index")
 
     val patternStr = new String(patternVec.get(0), StandardCharsets.UTF_8)
-    val pattern = {
-      val cached = patternCache.get(patternStr)
-      if (cached != null) cached
-      else {
-        val compiled = Pattern.compile(patternStr)
-        patternCache.put(patternStr, compiled)
-        compiled
-      }
-    }
+    val pattern = patternCache.computeIfAbsent(patternStr, Pattern.compile)
     val idx = idxVec.get(0)
 
     val n = subject.getValueCount

common/src/main/scala/org/apache/comet/udf/RegExpExtractUDF.scala

@@ -57,15 +57,7 @@ class RegExpExtractUDF extends CometUDF {
       "RegExpExtractUDF requires a non-null scalar group index")
 
     val patternStr = new String(patternVec.get(0), StandardCharsets.UTF_8)
-    val pattern = {
-      val cached = patternCache.get(patternStr)
-      if (cached != null) cached
-      else {
-        val compiled = Pattern.compile(patternStr)
-        patternCache.put(patternStr, compiled)
-        compiled
-      }
-    }
+    val pattern = patternCache.computeIfAbsent(patternStr, Pattern.compile)
     val idx = idxVec.get(0)
 
     val n = subject.getValueCount

common/src/main/scala/org/apache/comet/udf/RegExpInStrUDF.scala

@@ -57,15 +57,7 @@ class RegExpInStrUDF extends CometUDF {
       "RegExpInStrUDF requires a non-null scalar group index")
 
     val patternStr = new String(patternVec.get(0), StandardCharsets.UTF_8)
-    val pattern = {
-      val cached = patternCache.get(patternStr)
-      if (cached != null) cached
-      else {
-        val compiled = Pattern.compile(patternStr)
-        patternCache.put(patternStr, compiled)
-        compiled
-      }
-    }
+    val pattern = patternCache.computeIfAbsent(patternStr, Pattern.compile)
     val idx = idxVec.get(0)
 
     val n = subject.getValueCount

common/src/main/scala/org/apache/comet/udf/RegExpLikeUDF.scala

@@ -49,15 +49,7 @@ class RegExpLikeUDF extends CometUDF {
       "RegExpLikeUDF requires a non-null scalar pattern")
 
     val patternStr = new String(patternVec.get(0), StandardCharsets.UTF_8)
-    val pattern = {
-      val cached = patternCache.get(patternStr)
-      if (cached != null) cached
-      else {
-        val compiled = Pattern.compile(patternStr)
-        patternCache.put(patternStr, compiled)
-        compiled
-      }
-    }
+    val pattern = patternCache.computeIfAbsent(patternStr, Pattern.compile)
 
     val n = subject.getValueCount
     val out = new BitVector("rlike_result", CometArrowAllocator)

common/src/main/scala/org/apache/comet/udf/RegExpReplaceUDF.scala

@@ -56,15 +56,7 @@ class RegExpReplaceUDF extends CometUDF {
       "RegExpReplaceUDF requires a non-null scalar replacement")
 
     val patternStr = new String(patternVec.get(0), StandardCharsets.UTF_8)
-    val pattern = {
-      val cached = patternCache.get(patternStr)
-      if (cached != null) cached
-      else {
-        val compiled = Pattern.compile(patternStr)
-        patternCache.put(patternStr, compiled)
-        compiled
-      }
-    }
+    val pattern = patternCache.computeIfAbsent(patternStr, Pattern.compile)
     val replacement = new String(replacementVec.get(0), StandardCharsets.UTF_8)
 
     val n = subject.getValueCount

common/src/main/scala/org/apache/comet/udf/StringSplitUDF.scala

@@ -59,15 +59,7 @@ class StringSplitUDF extends CometUDF {
       "StringSplitUDF requires a non-null scalar limit")
 
     val patternStr = new String(patternVec.get(0), StandardCharsets.UTF_8)
-    val pattern = {
-      val cached = patternCache.get(patternStr)
-      if (cached != null) cached
-      else {
-        val compiled = Pattern.compile(patternStr)
-        patternCache.put(patternStr, compiled)
-        compiled
-      }
-    }
+    val pattern = patternCache.computeIfAbsent(patternStr, Pattern.compile)
     val limit = limitVec.get(0)
 
     val n = subject.getValueCount