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Commit 1ab9b864 authored by Neil Fuller's avatar Neil Fuller
Browse files

Switch ReferenceWithHistory to use ArrayDeque 

Switch ReferenceWithHistory to use ArrayDeque to avoid some object
creation.

Bug: 152405012
Test: atest ./services/tests/servicestests/src/com/android/server/timedetector
Change-Id: If09af2adb20eed615d6861fbe86f038812ea1438
parent 23b9d90b

services/core/java/com/android/server/timezonedetector/ReferenceWithHistory.java

+47 −12
Original line number Diff line number Diff line
@@ -22,7 +22,7 @@ import android.annotation.Nullable; 


import com.android.internal.util.IndentingPrintWriter;



import java.util.LinkedList;

import java.util.ArrayDeque;



/**

 * A class that behaves like the following definition, except it stores the history of values set
@@ -50,11 +50,18 @@ import java.util.LinkedList; 
 */

public final class ReferenceWithHistory<V> {



    /** The size the history linked list is allowed to grow to. */

    private static final Object NULL_MARKER = "{null marker}";



    /** The maximum number of references to store. */

    private final int mMaxHistorySize;



    /**

     * The history storage. Note that ArrayDeque doesn't support {@code null} so this stores Object

     * and not V. Use {@link #packNullIfRequired(Object)} and {@link #unpackNullIfRequired(Object)}

     * to convert to / from the storage object.

     */

    @Nullable

    private LinkedList<V> mValues;

    private ArrayDeque<Object> mValues;



    /**

     * Creates an instance that records, at most, the specified number of values.
@@ -69,22 +76,31 @@ public final class ReferenceWithHistory<V> { 
    /** Returns the current value, or {@code null} if it has never been set. */

    @Nullable

    public V get() {

        return (mValues == null || mValues.isEmpty()) ? null : mValues.getFirst();

        if (mValues == null || mValues.isEmpty()) {

            return null;

        }

        Object value = mValues.getFirst();

        return unpackNullIfRequired(value);

    }



    /** Sets the current value. Returns the previous value, or {@code null}. */

    /**

     * Sets the current value. Returns the previous value, which can be {@code null} if the

     * reference has never been set, or if the reference has been set to {@code null}.

     */

    @Nullable

    public V set(@Nullable V newValue) {

        if (mValues == null) {

            mValues = new LinkedList<>();

            mValues = new ArrayDeque<>(mMaxHistorySize);

        }



        V previous = get();



        mValues.addFirst(newValue);

        if (mValues.size() > mMaxHistorySize) {

        if (mValues.size() >= mMaxHistorySize) {

            mValues.removeLast();

        }



        V previous = get();



        Object nullSafeValue = packNullIfRequired(newValue);

        mValues.addFirst(nullSafeValue);

        return previous;

    }
@@ -96,8 +112,8 @@ public final class ReferenceWithHistory<V> { 
            ipw.println("{Empty}");

        } else {

            int i = 0;

            for (V value : mValues) {

                ipw.println(i + ": " + value);

            for (Object value : mValues) {

                ipw.println(i + ": " + unpackNullIfRequired(value));

                i++;

            }

        }
@@ -115,4 +131,23 @@ public final class ReferenceWithHistory<V> { 
    public String toString() {

        return String.valueOf(get());

    }



    /**

     * Turns a non-nullable Object into a nullable value. See also

     * {@link #packNullIfRequired(Object)}.

     */

    @SuppressWarnings("unchecked")

    @Nullable

    private V unpackNullIfRequired(@NonNull Object value) {

        return value == NULL_MARKER ? null : (V) value;

    }



    /**

     * Turns a nullable value into a non-nullable Object. See also

     * {@link #unpackNullIfRequired(Object)}.

     */

    @NonNull

    private Object packNullIfRequired(@Nullable V value) {

        return value == null ? NULL_MARKER : value;

    }

}