From 108485159cb030df4e5f35ea3de940865cf82496 Mon Sep 17 00:00:00 2001
From: Tim Murray <timmurray@google.com>
Date: Mon, 27 Feb 2023 16:59:15 -0800
Subject: [PATCH] AppProfiler: don't hold lock for CPU times

AppProfiler doesn't need to lock when calling getCpuTimeForPid or
getCpuDelayTimeForPid.

Additionally, ProcessCpuTracker is locking just for the sake of
avoiding a long[4] allocation, which might have been necessary in 2009
for dalvik but isn't a concern now.

Test: presubmit
Bug: 270905745
Change-Id: I585b6113734850ef200fa3faccc1f6decab9389d
---
 .../internal/os/ProcessCpuTracker.java        | 34 +++++++------------
 .../com/android/server/am/AppProfiler.java    |  8 ++---
 2 files changed, 15 insertions(+), 27 deletions(-)

diff --git a/core/java/com/android/internal/os/ProcessCpuTracker.java b/core/java/com/android/internal/os/ProcessCpuTracker.java
index 65655b7b5a662..70514c30d90d4 100644
--- a/core/java/com/android/internal/os/ProcessCpuTracker.java
+++ b/core/java/com/android/internal/os/ProcessCpuTracker.java
@@ -80,10 +80,6 @@ public class ProcessCpuTracker {
     /** Stores user time and system time in jiffies. */
     private final long[] mProcessStatsData = new long[4];
 
-    /** Stores user time and system time in jiffies.  Used for
-     * public API to retrieve CPU use for a process.  Must lock while in use. */
-    private final long[] mSinglePidStatsData = new long[4];
-
     private static final int[] PROCESS_FULL_STATS_FORMAT = new int[] {
         PROC_SPACE_TERM,
         PROC_SPACE_TERM|PROC_PARENS|PROC_OUT_STRING,    // 2: name
@@ -629,17 +625,15 @@ public class ProcessCpuTracker {
      * executing in both user and system code. Safe to call without lock held.
      */
     public long getCpuTimeForPid(int pid) {
-        synchronized (mSinglePidStatsData) {
-            final String statFile = "/proc/" + pid + "/stat";
-            final long[] statsData = mSinglePidStatsData;
-            if (Process.readProcFile(statFile, PROCESS_STATS_FORMAT,
-                    null, statsData, null)) {
-                long time = statsData[PROCESS_STAT_UTIME]
+        final String statFile = "/proc/" + pid + "/stat";
+        final long[] statsData = new long[4];
+        if (Process.readProcFile(statFile, PROCESS_STATS_FORMAT,
+                null, statsData, null)) {
+            long time = statsData[PROCESS_STAT_UTIME]
                         + statsData[PROCESS_STAT_STIME];
-                return time * mJiffyMillis;
-            }
-            return 0;
+            return time * mJiffyMillis;
         }
+        return 0;
     }
 
     /**
@@ -647,15 +641,13 @@ public class ProcessCpuTracker {
      * in the runqueue. Safe to call without lock held.
      */
     public long getCpuDelayTimeForPid(int pid) {
-        synchronized (mSinglePidStatsData) {
-            final String statFile = "/proc/" + pid + "/schedstat";
-            final long[] statsData = mSinglePidStatsData;
-            if (Process.readProcFile(statFile, PROCESS_SCHEDSTATS_FORMAT,
-                    null, statsData, null)) {
-                return statsData[PROCESS_SCHEDSTAT_CPU_DELAY_TIME] / 1_000_000;
-            }
-            return 0;
+        final String statFile = "/proc/" + pid + "/schedstat";
+        final long[] statsData = new long[4];
+        if (Process.readProcFile(statFile, PROCESS_SCHEDSTATS_FORMAT,
+                null, statsData, null)) {
+            return statsData[PROCESS_SCHEDSTAT_CPU_DELAY_TIME] / 1_000_000;
         }
+        return 0;
     }
 
     /**
diff --git a/services/core/java/com/android/server/am/AppProfiler.java b/services/core/java/com/android/server/am/AppProfiler.java
index 050ac194616fa..ac2c725ce80d3 100644
--- a/services/core/java/com/android/server/am/AppProfiler.java
+++ b/services/core/java/com/android/server/am/AppProfiler.java
@@ -1892,15 +1892,11 @@ public class AppProfiler {
     }
 
     long getCpuTimeForPid(int pid) {
-        synchronized (mProcessCpuTracker) {
-            return mProcessCpuTracker.getCpuTimeForPid(pid);
-        }
+        return mProcessCpuTracker.getCpuTimeForPid(pid);
     }
 
     long getCpuDelayTimeForPid(int pid) {
-        synchronized (mProcessCpuTracker) {
-            return mProcessCpuTracker.getCpuDelayTimeForPid(pid);
-        }
+        return mProcessCpuTracker.getCpuDelayTimeForPid(pid);
     }
 
     List<ProcessCpuTracker.Stats> getCpuStats(Predicate<ProcessCpuTracker.Stats> predicate) {