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/*
* Copyright (C) 2021 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package android.app.time;
import android.annotation.CurrentTimeMillisLong;
import android.annotation.ElapsedRealtimeLong;
import android.annotation.NonNull;
import android.annotation.Nullable;
import android.annotation.SystemApi;
import android.os.Parcel;
import android.os.Parcelable;
import android.os.TimestampedValue;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Objects;
/**
* A time signal from an External source.
*
* <p>External time suggestions are for use in situations where the Android device is part of a
* wider network of devices that are required to use a single time source, and where authority for
* the time is external to the Android device. For example, for the Android Auto use case where the
* Android device is part of a wider in-car network of devices that should display the same time.
*
* <p>Android allows for a single external source for time. If there are several external sources
* then it is left to the caller to prioritize / filter accordingly to ensure consistency.
*
* <p>External is one of several time "origins" that the Android platform supports. Stock Android
* allows for configuration of which origins can be used and the prioritization between them. Until
* an external suggestion is made, the Android device may use its own RTC to initialize the system
* clock during boot, and then accept suggestions from the configured origins.
*
* <p>The creator of an external suggestion is expected to be separate Android process, e.g. a
* process integrating with the external time source via a HAL or local network. The creator must
* capture the elapsed realtime reference clock, e.g. via {@link SystemClock#elapsedRealtime()},
* when the Unix epoch time is first obtained (usually under a wakelock). This enables Android to
* adjust for latency introduced between suggestion creation and eventual use. Adjustments for other
* sources of latency, i.e. those before the external time suggestion is created, must be handled by
* the creator.
*
* <p>{@code elapsedRealtimeMillis} and {@code suggestionMillis} represent the suggested time.
* {@code suggestionMillis} is the number of milliseconds elapsed since 1/1/1970 00:00:00 UTC
* according to the Unix time scale. {@code elapsedRealtimeMillis} is the value of the elapsed
* realtime clock when {@code suggestionMillis} was established. Note that the elapsed realtime
* clock is considered accurate but it is volatile, so time suggestions cannot be persisted across
* device resets.
*
* <p>{@code debugInfo} contains debugging metadata associated with the suggestion. This is used to
* record why the suggestion exists and how it was entered. This information exists only to aid in
* debugging and therefore is used by {@link #toString()}, but it is not for use in detection logic
* and is not considered in {@link #hashCode()} or {@link #equals(Object)}.
*
* @hide
*/
@SystemApi
public final class ExternalTimeSuggestion implements Parcelable {
public static final @NonNull Creator<ExternalTimeSuggestion> CREATOR =
new Creator<ExternalTimeSuggestion>() {
public ExternalTimeSuggestion createFromParcel(Parcel in) {
return ExternalTimeSuggestion.createFromParcel(in);
}
public ExternalTimeSuggestion[] newArray(int size) {
return new ExternalTimeSuggestion[size];
}
};
@NonNull
private final TimestampedValue<Long> mUnixEpochTime;
@Nullable
private ArrayList<String> mDebugInfo;
/**
* Creates a time suggestion cross-referenced to the elapsed realtime clock. See {@link
* ExternalTimeSuggestion} for more details.
*
* @param elapsedRealtimeMillis the elapsed realtime clock reference for the suggestion
* @param suggestionMillis the suggested time in milliseconds since the start of the
* Unix epoch
*/
public ExternalTimeSuggestion(@ElapsedRealtimeLong long elapsedRealtimeMillis,
@CurrentTimeMillisLong long suggestionMillis) {
mUnixEpochTime = new TimestampedValue(elapsedRealtimeMillis, suggestionMillis);
}
private static ExternalTimeSuggestion createFromParcel(Parcel in) {
TimestampedValue<Long> utcTime = in.readParcelable(null /* classLoader */);
ExternalTimeSuggestion suggestion =
new ExternalTimeSuggestion(utcTime.getReferenceTimeMillis(), utcTime.getValue());
@SuppressWarnings("unchecked")
ArrayList<String> debugInfo = (ArrayList<String>) in.readArrayList(null /* classLoader */);
suggestion.mDebugInfo = debugInfo;
return suggestion;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(@NonNull Parcel dest, int flags) {
dest.writeParcelable(mUnixEpochTime, 0);
dest.writeList(mDebugInfo);
}
/**
* {@hide}
*/
@NonNull
public TimestampedValue<Long> getUnixEpochTime() {
return mUnixEpochTime;
}
/**
* Returns information that can be useful for debugging / logging. See {@link #addDebugInfo}.
*/
@NonNull
public List<String> getDebugInfo() {
return mDebugInfo == null
? Collections.emptyList()
: Collections.unmodifiableList(mDebugInfo);
}
/**
* Associates information with the instance that can be useful for debugging / logging. The
* information is present in {@link #toString()} but is not considered for {@link
* #equals(Object)} and {@link #hashCode()}.
*/
public void addDebugInfo(@NonNull String... debugInfos) {
if (mDebugInfo == null) {
mDebugInfo = new ArrayList<>();
}
mDebugInfo.addAll(Arrays.asList(debugInfos));
}
@Override
public boolean equals(Object o) {
if (this == o) {
return true;
}
if (o == null || getClass() != o.getClass()) {
return false;
}
ExternalTimeSuggestion that = (ExternalTimeSuggestion) o;
return Objects.equals(mUnixEpochTime, that.mUnixEpochTime);
}
@Override
public int hashCode() {
return Objects.hash(mUnixEpochTime);
}
@Override
public String toString() {
return "ExternalTimeSuggestion{" + "mUnixEpochTime=" + mUnixEpochTime
+ ", mDebugInfo=" + mDebugInfo
+ '}';
}
}
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