From 05a6102a99a80f3b87966843c486e25c03351f63 Mon Sep 17 00:00:00 2001
From: Mikhail Bezoyan <mbezoyan@twitter.com>
Date: Fri, 4 Oct 2024 15:56:49 +0000
Subject: [PATCH] [scrooge] Preallocate hashmaps during deserialization

Problem
When a map is deserialized in scrooge we create it with default capacity, which means that for larger maps we need to resize it multiple times and each time recalculate key hashes

Solution
Allocate a map with sufficient capacity from the start.

Differential Revision: https://phabricator.twitter.biz/D1174445
---
 .../scala/com/twitter/scrooge/internal/TProtocols.scala   | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/scrooge-core/src/main/scala/com/twitter/scrooge/internal/TProtocols.scala b/scrooge-core/src/main/scala/com/twitter/scrooge/internal/TProtocols.scala
index b41241d9..be698227 100644
--- a/scrooge-core/src/main/scala/com/twitter/scrooge/internal/TProtocols.scala
+++ b/scrooge-core/src/main/scala/com/twitter/scrooge/internal/TProtocols.scala
@@ -3,6 +3,7 @@ package com.twitter.scrooge.internal
 import com.twitter.scrooge.TFieldBlob
 import com.twitter.scrooge.ThriftEnum
 import com.twitter.scrooge.ThriftUnion
+import com.twitter.util.MapUtil
 import java.nio.ByteBuffer
 import java.util.function.ObjDoubleConsumer
 import java.util.function.ObjLongConsumer
@@ -68,18 +69,19 @@ final class TProtocols private[TProtocols] {
     readValue: TProtocol => V
   ): collection.Map[K, V] = {
     val tmap = protocol.readMapBegin()
-    if (tmap.size == 0) {
+    val size = tmap.size
+    if (size == 0) {
       protocol.readMapEnd()
       Map.empty[K, V]
     } else {
-      val map = new mutable.HashMap[K, V]()
+      val map = MapUtil.newHashMap[K, V](size)
       var i = 0
       do {
         val key = readKey(protocol)
         val value = readValue(protocol)
         map(key) = value
         i += 1
-      } while (i < tmap.size)
+      } while (i < size)
       protocol.readMapEnd()
       map
     }