1 /*
2  * Copyright (C) 2023 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package com.android.app.tracing
18 
19 import android.os.Trace
20 import android.util.Log
21 
22 /**
23  * Utility class used to log state changes easily in a track with a custom name.
24  *
25  * Example of usage:
26  * ```kotlin
27  * class MyClass {
28  *    val screenStateLogger = TraceStateLogger("Screen state")
29  *
30  *    fun onTurnedOn() { screenStateLogger.log("on") }
31  *    fun onTurnedOff() { screenStateLogger.log("off") }
32  * }
33  * ```
34  *
35  * This creates a new slice in a perfetto trace only if the state is different than the previous
36  * one.
37  */
38 public class TraceStateLogger
39 @JvmOverloads
40 constructor(
41     private val trackName: String,
42     private val logOnlyIfDifferent: Boolean = true,
43     private val instantEvent: Boolean = true,
44     private val logcat: Boolean = false,
45 ) {
46 
47     private var previousValue: String? = null
48 
49     /** If needed, logs the value to a track with name [trackName]. */
lognull50     public fun log(newValue: String) {
51         if (instantEvent) {
52             Trace.instantForTrack(Trace.TRACE_TAG_APP, trackName, newValue)
53         }
54         if (logOnlyIfDifferent && previousValue == newValue) return
55         if (previousValue != null) {
56             Trace.asyncTraceForTrackEnd(Trace.TRACE_TAG_APP, trackName, 0)
57         }
58         Trace.asyncTraceForTrackBegin(Trace.TRACE_TAG_APP, trackName, newValue, 0)
59         if (logcat) {
60             Log.d(trackName, "newValue: $newValue")
61         }
62         previousValue = newValue
63     }
64 }
65