From 915e6c11af87401c8af385d28ebd09208325ee4f Mon Sep 17 00:00:00 2001
From: Zim <zezeozue@google.com>
Date: Tue, 20 Sep 2022 17:05:22 +0100
Subject: [PATCH] Populate binder trace txn names lazily

Previously, for each binder interface, we populated a cache of all
txn codes to names on the first binder txn to that interface. This
skewed the binder txn latency significantly for the first txn to an
interface.

Now, we lazily populate the cache on each new binder txn.

Test: atest open-prebuilt-calculator --rebuild-module-info
--tf-template metric_post_processor=
google/template/postprocessors/metric-file-aggregate.xml
(neglible startup time diff locally)
Bug: 246650647

Change-Id: Ib569ebe34e7ef6bb4fa6e53defedcb33ed824308
---
 core/java/android/os/Binder.java | 41 ++++++++++++++++++--------------
 1 file changed, 23 insertions(+), 18 deletions(-)

diff --git a/core/java/android/os/Binder.java b/core/java/android/os/Binder.java
index 4f26ad2b4f52e..a539e6aaca80c 100644
--- a/core/java/android/os/Binder.java
+++ b/core/java/android/os/Binder.java
@@ -46,6 +46,7 @@ import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.lang.reflect.Modifier;
+import java.util.concurrent.atomic.AtomicReferenceArray;
 
 /**
  * Base class for a remotable object, the core part of a lightweight
@@ -313,7 +314,7 @@ public class Binder implements IBinder {
     private IInterface mOwner;
     @Nullable
     private String mDescriptor;
-    private volatile String[] mTransactionTraceNames = null;
+    private volatile AtomicReferenceArray<String> mTransactionTraceNames = null;
     private volatile String mSimpleDescriptor = null;
     private static final int TRANSACTION_TRACE_NAME_ID_LIMIT = 1024;
 
@@ -917,28 +918,32 @@ public class Binder implements IBinder {
     @VisibleForTesting
     public final @NonNull String getTransactionTraceName(int transactionCode) {
         if (mTransactionTraceNames == null) {
-            final String descriptor = getSimpleDescriptor();
             final int highestId = Math.min(getMaxTransactionId(), TRANSACTION_TRACE_NAME_ID_LIMIT);
-            final String[] transactionNames = new String[highestId + 1];
-            final StringBuffer buf = new StringBuffer();
-            for (int i = 0; i <= highestId; i++) {
-                String transactionName = getTransactionName(i + FIRST_CALL_TRANSACTION);
-                if (transactionName != null) {
-                    buf.append(descriptor).append(':').append(transactionName);
-                } else {
-                    buf.append(descriptor).append('#').append(i + FIRST_CALL_TRANSACTION);
-                }
-                transactionNames[i] = buf.toString();
-                buf.setLength(0);
-            }
-            mSimpleDescriptor = descriptor;
-            mTransactionTraceNames = transactionNames;
+            mSimpleDescriptor = getSimpleDescriptor();
+            mTransactionTraceNames = new AtomicReferenceArray(highestId + 1);
         }
+
         final int index = transactionCode - FIRST_CALL_TRANSACTION;
-        if (index < 0 || index >= mTransactionTraceNames.length) {
+        if (index < 0 || index >= mTransactionTraceNames.length()) {
             return mSimpleDescriptor + "#" + transactionCode;
         }
-        return mTransactionTraceNames[index];
+
+        String transactionTraceName = mTransactionTraceNames.getAcquire(index);
+        if (transactionTraceName == null) {
+            final String transactionName = getTransactionName(transactionCode);
+            final StringBuffer buf = new StringBuffer();
+
+            if (transactionName != null) {
+                buf.append(mSimpleDescriptor).append(":").append(transactionName);
+            } else {
+                buf.append(mSimpleDescriptor).append("#").append(transactionCode);
+            }
+
+            transactionTraceName = buf.toString();
+            mTransactionTraceNames.setRelease(index, transactionTraceName);
+        }
+
+        return transactionTraceName;
     }
 
     private @NonNull String getSimpleDescriptor() {