Merge "Remove obsolete AnrTimer Java code" into main

2 files changed, 94 insertions, 650 deletions

diff --git a/services/core/java/com/android/server/utils/AnrTimer.java b/services/core/java/com/android/server/utils/AnrTimer.java
index 2b6dffb2b271..7b5192c4bd6b 100644
--- a/services/core/java/com/android/server/utils/AnrTimer.java
+++ b/services/core/java/com/android/server/utils/AnrTimer.java
@@ -16,37 +16,22 @@
 
 package com.android.server.utils;
 
-import static android.text.TextUtils.formatSimple;
-
-import android.annotation.IntDef;
 import android.annotation.NonNull;
-import android.annotation.Nullable;
 import android.os.Handler;
-import android.os.Looper;
 import android.os.Message;
-import android.os.Process;
 import android.os.SystemClock;
 import android.os.Trace;
-import android.text.TextUtils;
 import android.text.format.TimeMigrationUtils;
-import android.util.ArrayMap;
 import android.util.IndentingPrintWriter;
 import android.util.Log;
-import android.util.MathUtils;
-import android.util.SparseArray;
 
 import com.android.internal.annotations.GuardedBy;
-import com.android.internal.annotations.Keep;
 import com.android.internal.annotations.VisibleForTesting;
-import com.android.internal.os.ProcessCpuTracker;
 import com.android.internal.util.RingBuffer;
 
 import java.io.PrintWriter;
-import java.lang.ref.WeakReference;
-import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Objects;
-import java.util.concurrent.atomic.AtomicInteger;
 
 /**
  * This class managers AnrTimers.  An AnrTimer is a substitute for a delayed Message.  In legacy
@@ -102,12 +87,6 @@ public class AnrTimer<V> {
     private static final long TRACE_TAG = Trace.TRACE_TAG_ACTIVITY_MANAGER;
 
     /**
-     * Enable tracing from the time a timer expires until it is accepted or discarded.  This is
-     * used to diagnose long latencies in the client.
-     */
-    private static final boolean ENABLE_TRACING = false;
-
-    /**
      * Return true if the feature is enabled.  By default, the value is take from the Flags class
      * but it can be changed for local testing.
      */
@@ -116,22 +95,13 @@ public class AnrTimer<V> {
     }
 
     /**
-     * The status of an ANR timer.  TIMER_INVALID status is returned when an error is detected.
+     * This class allows test code to provide instance-specific overrides.
      */
-    private static final int TIMER_INVALID = 0;
-    private static final int TIMER_RUNNING = 1;
-    private static final int TIMER_EXPIRED = 2;
-
-    @IntDef(prefix = { "TIMER_" }, value = {
-                TIMER_INVALID, TIMER_RUNNING, TIMER_EXPIRED
-            })
-    private @interface TimerStatus {}
-
-    /**
-     * A static list of all known AnrTimer instances, used for dumping and testing.
-     */
-    @GuardedBy("sAnrTimerList")
-    private static final ArrayList<WeakReference<AnrTimer>> sAnrTimerList = new ArrayList<>();
+    static class Injector {
+        boolean anrTimerServiceEnabled() {
+            return AnrTimer.anrTimerServiceEnabled();
+        }
+    }
 
     /**
      * An error is defined by its issue, the operation that detected the error, the tag of the
@@ -161,6 +131,22 @@ public class AnrTimer<V> {
             this.arg = arg;
             this.timestamp = SystemClock.elapsedRealtime();
         }
+
+        /**
+         * Dump a single error to the output stream.
+         */
+        private void dump(IndentingPrintWriter ipw, int seq) {
+            ipw.format("%2d: op:%s tag:%s issue:%s arg:%s\n", seq, operation, tag, issue, arg);
+
+            final long offset = System.currentTimeMillis() - SystemClock.elapsedRealtime();
+            final long etime = offset + timestamp;
+            ipw.println("    date:" + TimeMigrationUtils.formatMillisWithFixedFormat(etime));
+            ipw.increaseIndent();
+            for (int i = 0; i < stack.length; i++) {
+                ipw.println("    " + stack[i].toString());
+            }
+            ipw.decreaseIndent();
+        }
     }
 
     /**
@@ -171,132 +157,10 @@ public class AnrTimer<V> {
     @GuardedBy("sErrors")
     private static final RingBuffer<Error> sErrors = new RingBuffer<>(Error.class, 20);
 
-    /**
-     * A record of a single anr timer.  The pid and uid are retained for reference but they do not
-     * participate in the equality tests. A {@link Timer} is bound to its parent {@link AnrTimer}
-     * through the owner field.  Access to timer fields is guarded by the mLock of the owner.
-     */
-    private static class Timer {
-        /** The AnrTimer that is managing this Timer. */
-        final AnrTimer owner;
-
-        /** The argument that uniquely identifies the Timer in the context of its current owner. */
-        final Object arg;
-        /** The pid of the process being tracked by this Timer. */
-        final int pid;
-        /** The uid of the process being tracked by this Timer as reported by the kernel. */
-        final int uid;
-        /** The original timeout. */
-        final long timeoutMs;
-
-        /** The status of the Timer.  */
-        @GuardedBy("owner.mLock")
-        @TimerStatus
-        int status;
-
-        /** The absolute time the timer was startd */
-        final long startedMs;
-
-        /** Fields used by the native timer service. */
-
-        /** The timer ID: used to exchange information with the native service. */
-        int timerId;
-
-        /** Fields used by the legacy timer service. */
-
-        /**
-         * The process's cpu delay time when the timer starts . It is meaningful only if
-         * extendable is true.  The cpu delay is cumulative, so the incremental delay that occurs
-         * during a timer is the delay at the end of the timer minus this value.  Units are in
-         * milliseconds.
-         */
-        @GuardedBy("owner.mLock")
-        long initialCpuDelayMs;
-
-        /** True if the timer has been extended. */
-        @GuardedBy("owner.mLock")
-        boolean extended;
-
-        /**
-         * Fetch a new Timer.  This is private.  Clients should get a new timer using the obtain()
-         * method.
-         */
-        private Timer(int pid, int uid, @Nullable Object arg, long timeoutMs,
-                @NonNull AnrTimer service) {
-            this.arg = arg;
-            this.pid = pid;
-            this.uid = uid;
-            this.timerId = 0;
-            this.timeoutMs = timeoutMs;
-            this.startedMs = now();
-            this.owner = service;
-            this.initialCpuDelayMs = 0;
-            this.extended = false;
-            this.status = TIMER_INVALID;
-        }
-
-        /** Get a timer.  This implementation constructs a new timer. */
-        static Timer obtain(int pid, int uid, @Nullable Object arg, long timeout,
-                @NonNull AnrTimer service) {
-            return new Timer(pid, uid, arg, timeout, service);
-        }
-
-        /** Release a timer. This implementation simply drops the timer. */
-        void release() {
-        }
-
-        /** Return the age of the timer. This is used for debugging. */
-        long age() {
-            return now() - startedMs;
-        }
-
-        /**
-         * The hash code is generated from the owner and the argument.  By definition, the
-         * combination must be unique for the lifetime of an in-use Timer.
-         */
-        @Override
-        public int hashCode() {
-            return Objects.hash(owner, arg);
-        }
-
-        /**
-         * The equality check compares the owner and the argument.  By definition, the combination
-         * must be unique for the lifetime of an in-use Timer.
-         */
-        @Override
-        public boolean equals(Object r) {
-            if (r instanceof Timer) {
-                Timer t = (Timer) r;
-                return Objects.equals(owner, t.owner) && Objects.equals(arg, t.arg);
-            }
-            return false;
-        }
-
-        @Override
-        public String toString() {
-            final int myStatus;
-            synchronized (owner.mLock) {
-                myStatus = status;
-            }
-            return "timerId=" + timerId + " pid=" + pid + " uid=" + uid
-                    + " " + statusString(myStatus) + " " + owner.mLabel;
-        }
-    }
-
     /** A lock for the AnrTimer instance. */
     private final Object mLock = new Object();
 
     /**
-     * The map from client argument to the associated timer.
-     */
-    @GuardedBy("mLock")
-    private final ArrayMap<V, Timer> mTimerMap = new ArrayMap<>();
-
-    /** The highwater mark of started, but not closed, timers. */
-    @GuardedBy("mLock")
-    private int mMaxStarted = 0;
-
-    /**
      * The total number of timers started.
      */
     @GuardedBy("mLock")
@@ -309,176 +173,6 @@ public class AnrTimer<V> {
     private int mTotalErrors = 0;
 
     /**
-     * The total number of timers that have expired.
-     */
-    @GuardedBy("mLock")
-    private int mTotalExpired = 0;
-
-    /**
-     * A TimerService that generates a timeout event <n> milliseconds in the future.  See the
-     * class documentation for an explanation of the operations.
-     */
-    private abstract class TimerService {
-        /** Start a timer.  The timeout must be initialized. */
-        abstract boolean start(@NonNull Timer timer);
-
-        abstract void cancel(@NonNull Timer timer);
-
-        abstract void accept(@NonNull Timer timer);
-
-        abstract void discard(@NonNull Timer timer);
-    }
-
-    /**
-     * A class to assist testing.  All methods are null by default but can be overridden as
-     * necessary for a test.
-     */
-    @VisibleForTesting
-    static class Injector {
-        private final Handler mReferenceHandler;
-
-        Injector(@NonNull Handler handler) {
-            mReferenceHandler = handler;
-        }
-
-        /**
-         * Return a handler for the given Callback, based on the reference handler. The handler
-         * might be mocked, in which case it does not have a valid Looper.  In this case, use the
-         * main Looper.
-         */
-        @NonNull
-        Handler newHandler(@NonNull Handler.Callback callback) {
-            Looper looper = mReferenceHandler.getLooper();
-            if (looper == null) looper = Looper.getMainLooper();
-            return new Handler(looper, callback);
-        }
-
-        /**
-         * Return a CpuTracker. The default behavior is to create a new CpuTracker but this changes
-         * for unit tests.
-         **/
-        @NonNull
-        CpuTracker newTracker() {
-            return new CpuTracker();
-        }
-
-        /** Return true if the feature is enabled. */
-        boolean isFeatureEnabled() {
-            return anrTimerServiceEnabled();
-        }
-    }
-
-    /**
-     * A helper class to measure CPU delays.  Given a process ID, this class will return the
-     * cumulative CPU delay for the PID, since process inception.  This class is defined to assist
-     * testing.
-     */
-    @VisibleForTesting
-    static class CpuTracker {
-        /**
-         * The parameter to ProcessCpuTracker indicates that statistics should be collected on a
-         * single process and not on the collection of threads associated with that process.
-         */
-        private final ProcessCpuTracker mCpu = new ProcessCpuTracker(false);
-
-        /** A simple wrapper to fetch the delay.  This method can be overridden for testing. */
-        long delay(int pid) {
-            return mCpu.getCpuDelayTimeForPid(pid);
-        }
-    }
-
-    /**
-     * The "user-space" implementation of the timer service.  This service uses its own message
-     * handler to create timeouts.
-     */
-    private class HandlerTimerService extends TimerService {
-        /** The lock for this handler */
-        private final Object mLock = new Object();
-
-        /** The message handler for scheduling future events. */
-        private final Handler mHandler;
-
-        /** The interface to fetch process statistics that might extend an ANR timeout. */
-        private final CpuTracker mCpu;
-
-        /** Create a HandlerTimerService that directly uses the supplied handler and tracker. */
-        @VisibleForTesting
-        HandlerTimerService(@NonNull Injector injector) {
-            mHandler = injector.newHandler(this::expires);
-            mCpu = injector.newTracker();
-        }
-
-        /** Post a message with the specified timeout.  The timer is not modified. */
-        private void post(@NonNull Timer t, long timeoutMillis) {
-            final Message msg = mHandler.obtainMessage();
-            msg.obj = t;
-            mHandler.sendMessageDelayed(msg, timeoutMillis);
-        }
-
-        /**
-         * The local expiration handler first attempts to compute a timer extension.  If the timer
-         * should be extended, it is rescheduled in the future (granting more time to the
-         * associated process).  If the timer should not be extended then the timeout is delivered
-         * to the client.
-         *
-         * A process is extended to account for the time the process was swapped out and was not
-         * runnable through no fault of its own.  A timer can only be extended once and only if
-         * the AnrTimer permits extensions.  Finally, a timer will never be extended by more than
-         * the original timeout, so the total timeout will never be more than twice the originally
-         * configured timeout.
-         */
-        private boolean expires(Message msg) {
-            Timer t = (Timer) msg.obj;
-            synchronized (mLock) {
-                long extension = 0;
-                if (mExtend && !t.extended) {
-                    extension = mCpu.delay(t.pid) - t.initialCpuDelayMs;
-                    if (extension < 0) extension = 0;
-                    if (extension > t.timeoutMs) extension = t.timeoutMs;
-                    t.extended = true;
-                }
-                if (extension > 0) {
-                    post(t, extension);
-                } else {
-                    onExpiredLocked(t);
-                }
-            }
-            return true;
-        }
-
-        @GuardedBy("mLock")
-        @Override
-        boolean start(@NonNull Timer t) {
-            if (mExtend) {
-                t.initialCpuDelayMs = mCpu.delay(t.pid);
-            }
-            post(t, t.timeoutMs);
-            return true;
-        }
-
-        @Override
-        void cancel(@NonNull Timer t) {
-            mHandler.removeMessages(0, t);
-        }
-
-        @Override
-        void accept(@NonNull Timer t) {
-            // Nothing to do.
-        }
-
-        @Override
-        void discard(@NonNull Timer t) {
-            // Nothing to do.
-        }
-
-        /** The string identifies this subclass of AnrTimerService as being based on handlers. */
-        @Override
-        public String toString() {
-            return "handler";
-        }
-    }
-
-    /**
      * The handler for messages sent from this instance.
      */
     private final Handler mHandler;
@@ -499,18 +193,6 @@ public class AnrTimer<V> {
     private final boolean mExtend;
 
     /**
-     * The timer service to use for this AnrTimer.
-     */
-    private final TimerService mTimerService;
-
-    /**
-     * Whether or not canceling a non-existent timer is an error.  Clients often cancel freely
-     * preemptively, without knowing if the timer was ever started.  Keeping this variable true
-     * means that such behavior is not an error.
-     */
-    private final boolean mLenientCancel = true;
-
-    /**
      * The top-level switch for the feature enabled or disabled.
      */
     private final FeatureSwitch mFeature;
@@ -528,40 +210,34 @@ public class AnrTimer<V> {
      * AnrTimer may extend the individual timer rather than immediately delivering the timeout to
      * the client.  The extension policy is not part of the instance.
      *
-     * This method accepts an {@link #Injector} to tune behavior for testing.  This method should
-     * not be called directly by regular clients.
-     *
      * @param handler The handler to which the expiration message will be delivered.
      * @param what The "what" parameter for the expiration message.
      * @param label A name for this instance.
      * @param extend A flag to indicate if expired timers can be granted extensions.
-     * @param injector An {@link #Injector} to tune behavior for testing.
+     * @param injector An injector to provide overrides for testing.
      */
     @VisibleForTesting
     AnrTimer(@NonNull Handler handler, int what, @NonNull String label, boolean extend,
-            @NonNull Injector injector) {
+             @NonNull Injector injector) {
         mHandler = handler;
         mWhat = what;
         mLabel = label;
         mExtend = extend;
-        boolean enabled = injector.isFeatureEnabled();
-        if (!enabled) {
-            mFeature = new FeatureDisabled();
-            mTimerService = null;
-        } else {
-            mFeature = new FeatureEnabled();
-            mTimerService = new HandlerTimerService(injector);
-
-            synchronized (sAnrTimerList) {
-                sAnrTimerList.add(new WeakReference(this));
-            }
-        }
-        Log.i(TAG, formatSimple("created %s label: \"%s\"", mTimerService, label));
+        mFeature = new FeatureDisabled();
     }
 
     /**
-     * Create an AnrTimer instance with the default {@link #Injector}.  See {@link AnrTimer(Handler,
-     * int, String, boolean, Injector} for a functional description.
+     * Create one AnrTimer instance.  The instance is given a handler and a "what".  Individual
+     * timers are started with {@link #start}.  If a timer expires, then a {@link Message} is sent
+     * immediately to the handler with {@link Message.what} set to what and {@link Message.obj} set
+     * to the timer key.
+     *
+     * AnrTimer instances have a label, which must be unique.  The label is used for reporting and
+     * debug.
+     *
+     * If an individual timer expires internally, and the "extend" parameter is true, then the
+     * AnrTimer may extend the individual timer rather than immediately delivering the timeout to
+     * the client.  The extension policy is not part of the instance.
      *
      * @param handler The handler to which the expiration message will be delivered.
      * @param what The "what" parameter for the expiration message.
@@ -569,7 +245,7 @@ public class AnrTimer<V> {
      * @param extend A flag to indicate if expired timers can be granted extensions.
      */
     public AnrTimer(@NonNull Handler handler, int what, @NonNull String label, boolean extend) {
-        this(handler, what, label, extend, new Injector(handler));
+        this(handler, what, label, extend, new Injector());
     }
 
     /**
@@ -596,105 +272,17 @@ public class AnrTimer<V> {
     }
 
     /**
-     * Start a trace on the timer.  The trace is laid down in the AnrTimerTrack.
-     */
-    private void traceBegin(Timer t, String what) {
-        if (ENABLE_TRACING) {
-            final String label = formatSimple("%s(%d,%d,%s)", what, t.pid, t.uid, mLabel);
-            final int cookie = t.hashCode();
-            Trace.asyncTraceForTrackBegin(TRACE_TAG, TRACK, label, cookie);
-        }
-    }
-
-    /**
-     * End a trace on the timer.
-     */
-    private void traceEnd(Timer t) {
-        if (ENABLE_TRACING) {
-            final int cookie = t.hashCode();
-            Trace.asyncTraceForTrackEnd(TRACE_TAG, TRACK, cookie);
-        }
-    }
-
-    /**
-     * Return the string representation for a timer status.
-     */
-    private static String statusString(int s) {
-        switch (s) {
-            case TIMER_INVALID: return "invalid";
-            case TIMER_RUNNING: return "running";
-            case TIMER_EXPIRED: return "expired";
-        }
-        return formatSimple("unknown: %d", s);
-    }
-
-    /**
-     * Delete the timer associated with arg from the maps and return it.  Return null if the timer
-     * was not found.
-     */
-    @GuardedBy("mLock")
-    private Timer removeLocked(V arg) {
-        Timer timer = mTimerMap.remove(arg);
-        return timer;
-    }
-
-    /**
-     * Return the number of timers currently running.
-     */
-    @VisibleForTesting
-    static int sizeOfTimerList() {
-        synchronized (sAnrTimerList) {
-            int totalTimers = 0;
-            for (int i = 0; i < sAnrTimerList.size(); i++) {
-                AnrTimer client = sAnrTimerList.get(i).get();
-                if (client != null) totalTimers += client.mTimerMap.size();
-            }
-            return totalTimers;
-        }
-    }
-
-    /**
-     * Clear out all existing timers.  This will lead to unexpected behavior if used carelessly.
-     * It is available only for testing.  It returns the number of times that were actually
-     * erased.
-     */
-    @VisibleForTesting
-    static int resetTimerListForHermeticTest() {
-        synchronized (sAnrTimerList) {
-            int mapLen = 0;
-            for (int i = 0; i < sAnrTimerList.size(); i++) {
-                AnrTimer client = sAnrTimerList.get(i).get();
-                if (client != null) {
-                    mapLen += client.mTimerMap.size();
-                    client.mTimerMap.clear();
-                }
-            }
-            if (mapLen > 0) {
-                Log.w(TAG, formatSimple("erasing timer list: clearing %d timers", mapLen));
-            }
-            return mapLen;
-        }
-    }
-
-    /**
-     * Generate a log message for a timer.
-     */
-    private void report(@NonNull Timer timer, @NonNull String msg) {
-        Log.i(TAG, msg + " " + timer + " " + Objects.toString(timer.arg));
-    }
-
-    /**
      * The FeatureSwitch class provides a quick switch between feature-enabled behavior and
      * feature-disabled behavior.
      */
     private abstract class FeatureSwitch {
-        abstract boolean start(@NonNull V arg, int pid, int uid, long timeoutMs);
+        abstract void start(@NonNull V arg, int pid, int uid, long timeoutMs);
 
-        abstract boolean cancel(@NonNull V arg);
+        abstract void cancel(@NonNull V arg);
 
-        abstract boolean accept(@NonNull V arg);
+        abstract void accept(@NonNull V arg);
 
-        abstract boolean discard(@NonNull V arg);
+        abstract void discard(@NonNull V arg);
 
         abstract boolean enabled();
     }
@@ -706,29 +294,25 @@ public class AnrTimer<V> {
     private class FeatureDisabled extends FeatureSwitch {
         /** Start a timer by sending a message to the client's handler. */
         @Override
-        boolean start(@NonNull V arg, int pid, int uid, long timeoutMs) {
+        void start(@NonNull V arg, int pid, int uid, long timeoutMs) {
             final Message msg = mHandler.obtainMessage(mWhat, arg);
             mHandler.sendMessageDelayed(msg, timeoutMs);
-            return true;
         }
 
         /** Cancel a timer by removing the message from the client's handler. */
         @Override
-        boolean cancel(@NonNull V arg) {
+        void cancel(@NonNull V arg) {
             mHandler.removeMessages(mWhat, arg);
-            return true;
         }
 
         /** accept() is a no-op when the feature is disabled. */
         @Override
-        boolean accept(@NonNull V arg) {
-            return true;
+        void accept(@NonNull V arg) {
         }
 
         /** discard() is a no-op when the feature is disabled. */
         @Override
-        boolean discard(@NonNull V arg) {
-            return true;
+        void discard(@NonNull V arg) {
         }
 
         /** The feature is not enabled. */
@@ -739,113 +323,6 @@ public class AnrTimer<V> {
     }
 
     /**
-     * The FeatureEnabled class enables the AnrTimer logic.  It is used when the AnrTimer service
-     * is enabled via Flags.anrTimerServiceEnabled.
-     */
-    private class FeatureEnabled extends FeatureSwitch {
-
-        /**
-         * Start a timer.
-         */
-        @Override
-        boolean start(@NonNull V arg, int pid, int uid, long timeoutMs) {
-            final Timer timer = Timer.obtain(pid, uid, arg, timeoutMs, AnrTimer.this);
-            synchronized (mLock) {
-                Timer old = mTimerMap.get(arg);
-                // There is an existing timer.  If the timer was running, then cancel the running
-                // timer and restart it.  If the timer was expired record a protocol error and
-                // discard the expired timer.
-                if (old != null) {
-                    if (old.status == TIMER_EXPIRED) {
-                      restartedLocked(old.status, arg);
-                        discard(arg);
-                    } else {
-                        cancel(arg);
-                    }
-                }
-                if (mTimerService.start(timer)) {
-                    timer.status = TIMER_RUNNING;
-                    mTimerMap.put(arg, timer);
-                    mTotalStarted++;
-                    mMaxStarted = Math.max(mMaxStarted, mTimerMap.size());
-                    if (DEBUG) report(timer, "start");
-                    return true;
-                } else {
-                    Log.e(TAG, "AnrTimer.start failed");
-                    return false;
-                }
-            }
-        }
-
-        /**
-         * Cancel a timer.  Return false if the timer was not found.
-         */
-        @Override
-        boolean cancel(@NonNull V arg) {
-            synchronized (mLock) {
-                Timer timer = removeLocked(arg);
-                if (timer == null) {
-                    if (!mLenientCancel) notFoundLocked("cancel", arg);
-                    return false;
-                }
-                mTimerService.cancel(timer);
-                // There may be an expiration message in flight.  Cancel it.
-                mHandler.removeMessages(mWhat, arg);
-                if (DEBUG) report(timer, "cancel");
-                timer.release();
-                return true;
-            }
-        }
-
-        /**
-         * Accept a timer in the framework-level handler.  The timeout has been accepted and the
-         * timeout handler is executing.  Return false if the timer was not found.
-         */
-        @Override
-        boolean accept(@NonNull V arg) {
-            synchronized (mLock) {
-                Timer timer = removeLocked(arg);
-                if (timer == null) {
-                    notFoundLocked("accept", arg);
-                    return false;
-                }
-                mTimerService.accept(timer);
-                traceEnd(timer);
-                if (DEBUG) report(timer, "accept");
-                timer.release();
-                return true;
-            }
-        }
-
-        /**
-         * Discard a timer in the framework-level handler.  For whatever reason, the timer is no
-         * longer interesting.  No statistics are collected.  Return false if the time was not
-         * found.
-         */
-        @Override
-        boolean discard(@NonNull V arg) {
-            synchronized (mLock) {
-                Timer timer = removeLocked(arg);
-                if (timer == null) {
-                    notFoundLocked("discard", arg);
-                    return false;
-                }
-                mTimerService.discard(timer);
-                traceEnd(timer);
-                if (DEBUG) report(timer, "discard");
-                timer.release();
-                return true;
-            }
-        }
-
-        /** The feature is enabled. */
-        @Override
-        boolean enabled() {
-            return true;
-        }
-    }
-
-    /**
      * Start a timer associated with arg.  The same object must be used to cancel, accept, or
      * discard a timer later.  If a timer already exists with the same arg, then the existing timer
      * is canceled and a new timer is created.
@@ -854,32 +331,27 @@ public class AnrTimer<V> {
      * @param pid The Linux process ID of the target being timed.
      * @param uid The Linux user ID of the target being timed.
      * @param timeoutMs The timer timeout, in milliseconds.
-     * @return true if the timer was successfully created.
      */
-    public boolean start(@NonNull V arg, int pid, int uid, long timeoutMs) {
-        return mFeature.start(arg, pid, uid, timeoutMs);
+    public void start(@NonNull V arg, int pid, int uid, long timeoutMs) {
+        mFeature.start(arg, pid, uid, timeoutMs);
     }
 
     /**
      * Cancel the running timer associated with arg.  The timer is forgotten.  If the timer has
      * expired, the call is treated as a discard.  No errors are reported if the timer does not
      * exist or if the timer has expired.
-     *
-     * @return true if the timer was found and was running.
      */
-    public boolean cancel(@NonNull V arg) {
-        return mFeature.cancel(arg);
+    public void cancel(@NonNull V arg) {
+        mFeature.cancel(arg);
     }
 
     /**
      * Accept the expired timer associated with arg.  This indicates that the caller considers the
      * timer expiration to be a true ANR.  (See {@link #discard} for an alternate response.)  It is
      * an error to accept a running timer, however the running timer will be canceled.
-     *
-     * @return true if the timer was found and was expired.
      */
-    public boolean accept(@NonNull V arg) {
-        return mFeature.accept(arg);
+    public void accept(@NonNull V arg) {
+        mFeature.accept(arg);
     }
 
     /**
@@ -889,24 +361,9 @@ public class AnrTimer<V> {
      * such a process could be stopped at a breakpoint and its failure to respond would not be an
      * error.  It is an error to discard a running timer, however the running timer will be
      * canceled.
-     *
-     * @return true if the timer was found and was expired.
      */
-    public boolean discard(@NonNull V arg) {
-        return mFeature.discard(arg);
-    }
-
-    /**
-     * The notifier that a timer has fired.  The timer is not modified.
-     */
-    @GuardedBy("mLock")
-    private void onExpiredLocked(@NonNull Timer timer) {
-        if (DEBUG) report(timer, "expire");
-        traceBegin(timer, "expired");
-        mHandler.sendMessage(Message.obtain(mHandler, mWhat, timer.arg));
-        synchronized (mLock) {
-            mTotalExpired++;
-        }
+    public void discard(@NonNull V arg) {
+        mFeature.discard(arg);
     }
 
     /**
@@ -916,9 +373,7 @@ public class AnrTimer<V> {
         synchronized (mLock) {
             pw.format("timer: %s\n", mLabel);
             pw.increaseIndent();
-            pw.format("started=%d maxStarted=%d running=%d expired=%d error=%d\n",
-                    mTotalStarted, mMaxStarted, mTimerMap.size(),
-                    mTotalExpired, mTotalErrors);
+            pw.format("started=%d errors=%d\n", mTotalStarted, mTotalErrors);
             pw.decreaseIndent();
         }
     }
@@ -931,10 +386,20 @@ public class AnrTimer<V> {
     }
 
     /**
-     * The current time in milliseconds.
+     * Dump all errors to the output stream.
      */
-    private static long now() {
-        return SystemClock.uptimeMillis();
+    private static void dumpErrors(IndentingPrintWriter ipw) {
+        Error errors[];
+        synchronized (sErrors) {
+            if (sErrors.size() == 0) return;
+            errors = sErrors.toArray();
+        }
+        ipw.println("Errors");
+        ipw.increaseIndent();
+        for (int i = 0; i < errors.length; i++) {
+            if (errors[i] != null) errors[i].dump(ipw, i);
+        }
+        ipw.decreaseIndent();
     }
 
     /**
@@ -966,60 +431,12 @@ public class AnrTimer<V> {
     }
 
     /**
-     * Log an error about a timer that is started when there is an existing timer.
-     */
-    @GuardedBy("mLock")
-    private void restartedLocked(@TimerStatus int status, Object arg) {
-        recordErrorLocked("start", status == TIMER_EXPIRED ? "autoDiscard" : "autoCancel", arg);
-    }
-
-    /**
-     * Dump a single error to the output stream.
-     */
-    private static void dump(IndentingPrintWriter ipw, int seq, Error err) {
-        ipw.format("%2d: op:%s tag:%s issue:%s arg:%s\n", seq, err.operation, err.tag,
-                err.issue, err.arg);
-
-        final long offset = System.currentTimeMillis() - SystemClock.elapsedRealtime();
-        final long etime = offset + err.timestamp;
-        ipw.println("    date:" + TimeMigrationUtils.formatMillisWithFixedFormat(etime));
-        ipw.increaseIndent();
-        for (int i = 0; i < err.stack.length; i++) {
-            ipw.println("    " + err.stack[i].toString());
-        }
-        ipw.decreaseIndent();
-    }
-
-    /**
-     * Dump all errors to the output stream.
-     */
-    private static void dumpErrors(IndentingPrintWriter ipw) {
-        Error errors[];
-        synchronized (sErrors) {
-            if (sErrors.size() == 0) return;
-            errors = sErrors.toArray();
-        }
-        ipw.println("Errors");
-        ipw.increaseIndent();
-        for (int i = 0; i < errors.length; i++) {
-            if (errors[i] != null) dump(ipw, i, errors[i]);
-        }
-        ipw.decreaseIndent();
-    }
-
-    /**
      * Dumpsys output.
      */
     public static void dump(@NonNull PrintWriter pw, boolean verbose) {
         final IndentingPrintWriter ipw = new IndentingPrintWriter(pw);
         ipw.println("AnrTimer statistics");
         ipw.increaseIndent();
-        synchronized (sAnrTimerList) {
-            for (int i = 0; i < sAnrTimerList.size(); i++) {
-                AnrTimer client = sAnrTimerList.get(i).get();
-                if (client != null) client.dump(ipw);
-            }
-        }
         if (verbose) dumpErrors(ipw);
         ipw.format("AnrTimerEnd\n");
         ipw.decreaseIndent();
diff --git a/services/tests/servicestests/src/com/android/server/utils/AnrTimerTest.java b/services/tests/servicestests/src/com/android/server/utils/AnrTimerTest.java
index 330dbb83e949..861d14a2cf66 100644
--- a/services/tests/servicestests/src/com/android/server/utils/AnrTimerTest.java
+++ b/services/tests/servicestests/src/com/android/server/utils/AnrTimerTest.java
@@ -30,13 +30,19 @@ import androidx.test.filters.SmallTest;
 import com.android.internal.annotations.GuardedBy;
 
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
+import org.junit.runners.Parameterized.Parameters;
 
 import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
 
 @SmallTest
 @Presubmit
+@RunWith(Parameterized.class)
 public class AnrTimerTest {
 
     // The commonly used message timeout key.
@@ -106,6 +112,16 @@ public class AnrTimerTest {
     }
 
     /**
+     * Force AnrTimer to use the test parameter for the feature flag.
+     */
+    class TestInjector extends AnrTimer.Injector {
+        @Override
+        boolean anrTimerServiceEnabled() {
+            return mEnabled;
+        }
+    }
+
+    /**
      * An instrumented AnrTimer.
      */
     private static class TestAnrTimer extends AnrTimer<TestArg> {
@@ -137,6 +153,17 @@ public class AnrTimerTest {
         assertEquals(actual.what, MSG_TIMEOUT);
     }
 
+    @Parameters(name = "featureEnabled={0}")
+    public static Collection<Object[]> data() {
+        return Arrays.asList(new Object[][] { {false}, {true} });
+    }
+
+    /** True if the feature is enabled. */
+    private boolean mEnabled;
+
+    public AnrTimerTest(boolean featureEnabled) {
+        mEnabled = featureEnabled;
+    }
 
     /**
      * Verify that a simple expiration succeeds.  The timer is started for 10ms.  The test