1 /*
2  * Copyright 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 androidx.compose.runtime.snapshots
18 
19 import androidx.compose.runtime.Composition
20 import androidx.compose.runtime.internal.AtomicInt
21 import kotlin.jvm.JvmInline
22 
23 /**
24  * A [StateObject] that allows to record reader type when observed to optimize recording of
25  * modifications. Currently only reads in [Composition] and [SnapshotStateObserver] is supported.
26  * The methods are intentionally restricted to the internal types, as the API is expected to change.
27  */
28 internal abstract class StateObjectImpl internal constructor() : StateObject {
29     private val readerKind = AtomicInt(0)
30 
recordReadInnull31     internal fun recordReadIn(reader: ReaderKind) {
32         do {
33             val old = ReaderKind(readerKind.get())
34             if (old.isReadIn(reader)) return
35 
36             val new = old.withReadIn(reader)
37         } while (!readerKind.compareAndSet(old.mask, new.mask))
38     }
39 
isReadInnull40     internal fun isReadIn(reader: ReaderKind): Boolean =
41         ReaderKind(readerKind.get()).isReadIn(reader)
42 }
43 
44 @JvmInline
45 internal value class ReaderKind(val mask: Int = 0) {
46     @Suppress("NOTHING_TO_INLINE")
47     inline fun withReadIn(reader: ReaderKind): ReaderKind = ReaderKind(mask or reader.mask)
48 
49     @Suppress("NOTHING_TO_INLINE")
50     inline fun isReadIn(reader: ReaderKind): Boolean = mask and reader.mask != 0
51 
52     internal companion object {
53         inline val Composition
54             get() = ReaderKind(mask = 1 shl 0)
55 
56         inline val SnapshotStateObserver
57             get() = ReaderKind(mask = 1 shl 1)
58 
59         inline val SnapshotFlow
60             get() = ReaderKind(mask = 1 shl 2)
61     }
62 }
63