From 7c0faeeb6883c45dba7c3614d5739a127cb2c5a7 Mon Sep 17 00:00:00 2001
From: Shai Barack <shayba@google.com>
Date: Sat, 7 Jun 2025 19:46:06 -0700
Subject: [PATCH] Replace String.split() with precompiled regex

String.split() will allocate and compile the given regex on every call.
The networkstack process spends 2.8% of cycles doing this.

https://pprof.corp.google.com/?id=%2Fcns%2Fpf-d%2Fhome%2Fandroid-telemetry-pitot-pprof-prod-data-owner%2Fstack_sampling_pprof%2F2025-06-07%2Fstack-sampling-pprof-6187fab4-56da-4842-b9c3-9d8db45801d1.pb.gz&metric=samples&filter=hide:%255Enterp_helper%2524,focus:regex%257Csplit&pivot=com.android.networkstack.com.android.net.module.util.ProcfsParsingUtils

I randomly noticed this while looking at CPU profiles.

Flag: EXEMPT refactor
Test: ApfFilterTest and any others that may be exercising the code
Change-Id: I811c0e8982a87d10fedcda93379b08e8ab38a11b
---
 .../android/net/module/util/ProcfsParsingUtils.java   | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/staticlibs/device/com/android/net/module/util/ProcfsParsingUtils.java b/staticlibs/device/com/android/net/module/util/ProcfsParsingUtils.java
index 44fc94121b..573bbb1aed 100644
--- a/staticlibs/device/com/android/net/module/util/ProcfsParsingUtils.java
+++ b/staticlibs/device/com/android/net/module/util/ProcfsParsingUtils.java
@@ -35,6 +35,7 @@ import java.nio.file.Files;
 import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.regex.Pattern;
 
 public final class ProcfsParsingUtils {
     public static final String TAG = ProcfsParsingUtils.class.getSimpleName();
@@ -49,6 +50,8 @@ public final class ProcfsParsingUtils {
     private static final String IPV6_MCAST_PATH = "/proc/net/igmp6";
     private static final String IPV4_DEFAULT_TTL_PATH = "/proc/sys/net/ipv4/ip_default_ttl";
 
+    private static final Pattern WHITESPACE_PATTERN = Pattern.compile("\\s+");
+
     private ProcfsParsingUtils() {
     }
 
@@ -129,7 +132,7 @@ public final class ProcfsParsingUtils {
         final List<Inet6Address> addresses = new ArrayList<>();
         try {
             for (String line : lines) {
-                final String[] fields = line.split("\\s+");
+                final String[] fields = WHITESPACE_PATTERN.split(line);
                 if (!fields[1].equals(ifname)) {
                     continue;
                 }
@@ -156,7 +159,7 @@ public final class ProcfsParsingUtils {
             @NonNull List<String> lines, @NonNull String ifname) {
         final List<MacAddress> addresses = new ArrayList<>();
         for (String line: lines) {
-            final String[] fields = line.split("\\s+");
+            final String[] fields = WHITESPACE_PATTERN.split(line);
             if (!fields[1].equals(ifname)) {
                 continue;
             }
@@ -182,7 +185,7 @@ public final class ProcfsParsingUtils {
         final List<Inet6Address> addresses = new ArrayList<>();
         try {
             for (String line: lines) {
-                final String[] fields = line.split("\\s+");
+                final String[] fields = WHITESPACE_PATTERN.split(line);
                 if (!fields[1].equals(ifname)) {
                     continue;
                 }
@@ -217,7 +220,7 @@ public final class ProcfsParsingUtils {
             String name = "";
             // parse output similar to `ip maddr` command (iproute2/ip/ipmaddr.c#read_igmp())
             for (String line : lines) {
-                final String[] parts = line.trim().split("\\s+");
+                final String[] parts = WHITESPACE_PATTERN.split(line.trim());
                 if (!line.startsWith("\t")) {
                     name = parts[1];
                     if (name.endsWith(":")) {