Call Debug.getPss without a lock held

Attempt to reduce the chances of watchdog killing the system
server if process pss gathering takes too long during heavy load.

Bug: 30896716
Change-Id: I4ed1a15c0c512a8c82842cde74e733d99d887ee0

2 files changed, 46 insertions, 26 deletions

diff --git a/core/java/com/android/internal/os/ProcessCpuTracker.java b/core/java/com/android/internal/os/ProcessCpuTracker.java
index b7e571871086..e46dfc4e0cb6 100644
--- a/core/java/com/android/internal/os/ProcessCpuTracker.java
+++ b/core/java/com/android/internal/os/ProcessCpuTracker.java
@@ -39,6 +39,7 @@ import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Comparator;
 import java.util.Date;
+import java.util.List;
 import java.util.StringTokenizer;
 
 public class ProcessCpuTracker {
@@ -177,6 +178,11 @@ public class ProcessCpuTracker {
 
     private byte[] mBuffer = new byte[4096];
 
+    public interface FilterStats {
+        /** Which stats to pick when filtering */
+        boolean needed(Stats stats);
+    }
+
     public static class Stats {
         public final int pid;
         public final int uid;
@@ -695,6 +701,18 @@ public class ProcessCpuTracker {
         return mProcStats.get(index);
     }
 
+    final public List<Stats> getStats(FilterStats filter) {
+        final ArrayList<Stats> statses = new ArrayList<>(mProcStats.size());
+        final int N = mProcStats.size();
+        for (int p = 0; p < N; p++) {
+            Stats stats = mProcStats.get(p);
+            if (filter.needed(stats)) {
+                statses.add(stats);
+            }
+        }
+        return statses;
+    }
+
     final public int countWorkingStats() {
         buildWorkingProcs();
         return mWorkingProcs.size();
diff --git a/services/core/java/com/android/server/am/ActivityManagerService.java b/services/core/java/com/android/server/am/ActivityManagerService.java
index aedf089c8c1a..1dfca2b156da 100644
--- a/services/core/java/com/android/server/am/ActivityManagerService.java
+++ b/services/core/java/com/android/server/am/ActivityManagerService.java
@@ -2378,22 +2378,21 @@ public final class ActivityManagerService extends ActivityManagerNative
                 if (memInfo != null) {
                     updateCpuStatsNow();
                     long nativeTotalPss = 0;
+                    final List<ProcessCpuTracker.Stats> stats;
                     synchronized (mProcessCpuTracker) {
-                        final int N = mProcessCpuTracker.countStats();
-                        for (int j=0; j<N; j++) {
-                            ProcessCpuTracker.Stats st = mProcessCpuTracker.getStats(j);
-                            if (st.vsize <= 0 || st.uid >= Process.FIRST_APPLICATION_UID) {
-                                // This is definitely an application process; skip it.
+                        stats = mProcessCpuTracker.getStats( (st)-> {
+                            return st.vsize > 0 && st.uid < Process.FIRST_APPLICATION_UID;
+                        });
+                    }
+                    final int N = stats.size();
+                    for (int j = 0; j < N; j++) {
+                        synchronized (mPidsSelfLocked) {
+                            if (mPidsSelfLocked.indexOfKey(stats.get(j).pid) >= 0) {
+                                // This is one of our own processes; skip it.
                                 continue;
                             }
-                            synchronized (mPidsSelfLocked) {
-                                if (mPidsSelfLocked.indexOfKey(st.pid) >= 0) {
-                                    // This is one of our own processes; skip it.
-                                    continue;
-                                }
-                            }
-                            nativeTotalPss += Debug.getPss(st.pid, null, null);
                         }
+                        nativeTotalPss += Debug.getPss(stats.get(j).pid, null, null);
                     }
                     memInfo.readMemInfo();
                     synchronized (ActivityManagerService.this) {
@@ -16510,21 +16509,24 @@ public final class ActivityManagerService extends ActivityManagerNative
         }
         updateCpuStatsNow();
         long[] memtrackTmp = new long[1];
+        final List<ProcessCpuTracker.Stats> stats;
+        // Get a list of Stats that have vsize > 0
         synchronized (mProcessCpuTracker) {
-            final int N = mProcessCpuTracker.countStats();
-            for (int i=0; i<N; i++) {
-                ProcessCpuTracker.Stats st = mProcessCpuTracker.getStats(i);
-                if (st.vsize > 0) {
-                    long pss = Debug.getPss(st.pid, null, memtrackTmp);
-                    if (pss > 0) {
-                        if (infoMap.indexOfKey(st.pid) < 0) {
-                            ProcessMemInfo mi = new ProcessMemInfo(st.name, st.pid,
-                                    ProcessList.NATIVE_ADJ, -1, "native", null);
-                            mi.pss = pss;
-                            mi.memtrack = memtrackTmp[0];
-                            memInfos.add(mi);
-                        }
-                    }
+            stats = mProcessCpuTracker.getStats((st) -> {
+                return st.vsize > 0;
+            });
+        }
+        final int statsCount = stats.size();
+        for (int i = 0; i < statsCount; i++) {
+            ProcessCpuTracker.Stats st = stats.get(i);
+            long pss = Debug.getPss(st.pid, null, memtrackTmp);
+            if (pss > 0) {
+                if (infoMap.indexOfKey(st.pid) < 0) {
+                    ProcessMemInfo mi = new ProcessMemInfo(st.name, st.pid,
+                            ProcessList.NATIVE_ADJ, -1, "native", null);
+                    mi.pss = pss;
+                    mi.memtrack = memtrackTmp[0];
+                    memInfos.add(mi);
                 }
             }
         }