GlobalSnapshotManager.kt
/*
* Copyright 2022 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 androidx.glance.session
import androidx.annotation.RestrictTo
import androidx.compose.runtime.snapshots.Snapshot
import java.util.concurrent.atomic.AtomicBoolean
import kotlinx.coroutines.CoroutineScope
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.channels.Channel
import kotlinx.coroutines.channels.consumeEach
import kotlinx.coroutines.launch
/**
* Mechanism for glance sessions to start a monitor of global snapshot state writes in order to
* schedule periodic dispatch of apply notifications.
* Sessions should call [ensureStarted] during setup to initialize periodic global snapshot
* notifications (which are necessary in order for recompositions to be scheduled in response to
* state changes). These will be sent on Dispatchers.Default.
* This is based on [androidx.compose.ui.platform.GlobalSnapshotManager].
* @suppress
*/
@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
object GlobalSnapshotManager {
private val started = AtomicBoolean(false)
fun ensureStarted() {
if (started.compareAndSet(false, true)) {
val channel = Channel<Unit>(Channel.CONFLATED)
CoroutineScope(Dispatchers.Default).launch {
channel.consumeEach {
Snapshot.sendApplyNotifications()
}
}
Snapshot.registerGlobalWriteObserver {
channel.trySend(Unit)
}
}
}
}
/**
* Monitors global snapshot state writes and sends apply notifications.
*/
internal suspend fun globalSnapshotMonitor() {
val channel = Channel<Unit>(Channel.CONFLATED)
val observerHandle = Snapshot.registerGlobalWriteObserver {
channel.trySend(Unit)
}
try {
channel.consumeEach {
Snapshot.sendApplyNotifications()
}
} finally {
observerHandle.dispose()
}
}