InvalidateCallbackTracker.kt
/*
* Copyright 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 androidx.paging
import androidx.annotation.VisibleForTesting
import java.util.concurrent.locks.ReentrantLock
import kotlin.concurrent.withLock
/**
* Helper class for thread-safe invalidation callback tracking + triggering on registration.
*/
internal class InvalidateCallbackTracker<T>(
private val callbackInvoker: (T) -> Unit,
/**
* User-provided override of DataSource.isInvalid
*/
private val invalidGetter: (() -> Boolean)? = null,
) {
private val lock = ReentrantLock()
private val callbacks = mutableListOf<T>()
internal var invalid = false
private set
@VisibleForTesting
internal fun callbackCount() = callbacks.size
internal fun registerInvalidatedCallback(callback: T) {
// This isn't sufficient, but is the best we can do in cases where DataSource.isInvalid
// is overridden, since we have no way of knowing when the result gets flipped if user
// never calls .invalidate().
if (invalidGetter?.invoke() == true) {
invalidate()
}
if (invalid) {
callbackInvoker(callback)
return
}
var callImmediately = false
lock.withLock {
if (invalid) {
callImmediately = true
} else {
callbacks.add(callback)
}
}
if (callImmediately) {
callbackInvoker(callback)
}
}
internal fun unregisterInvalidatedCallback(callback: T) {
lock.withLock {
callbacks.remove(callback)
}
}
internal fun invalidate(): Boolean {
if (invalid) return false
var callbacksToInvoke: List<T>?
lock.withLock {
if (invalid) return false
invalid = true
callbacksToInvoke = callbacks.toList()
callbacks.clear()
}
callbacksToInvoke?.forEach(callbackInvoker)
return true
}
}