mirror of https://github.com/M66B/FairEmail.git
131 lines
4.8 KiB
Kotlin
131 lines
4.8 KiB
Kotlin
/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package androidx.lifecycle
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import androidx.annotation.RestrictTo
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import androidx.annotation.VisibleForTesting
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import androidx.annotation.WorkerThread
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import androidx.arch.core.executor.ArchTaskExecutor
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import java.util.concurrent.Executor
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import java.util.concurrent.atomic.AtomicBoolean
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/**
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* A LiveData class that can be invalidated & computed when there are active observers.
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*
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* It can be invalidated via [invalidate], which will result in a call to
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* [compute] if there are active observers (or when they start observing)
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*
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* This is an internal class for now, might be public if we see the necessity.
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*
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* @param <T> The type of the live data
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* @hide internal
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*/
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@RestrictTo(RestrictTo.Scope.LIBRARY_GROUP_PREFIX)
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abstract class ComputableLiveData<T> @JvmOverloads
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/**
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* Creates a computable live data that computes values on the specified executor
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* or the arch IO thread executor by default.
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*
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* @param executor Executor that is used to compute new LiveData values.
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*/
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constructor(
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internal val executor: Executor = ArchTaskExecutor.getIOThreadExecutor()
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) {
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private val _liveData: LiveData<T?> =
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object : LiveData<T?>() {
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override fun onActive() {
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executor.execute(refreshRunnable)
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}
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}
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/**
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* The LiveData managed by this class.
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*/
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open val liveData: LiveData<T?> = _liveData
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internal val invalid = AtomicBoolean(true)
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internal val computing = AtomicBoolean(false)
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@JvmField
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@VisibleForTesting
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internal val refreshRunnable = Runnable {
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var computed: Boolean
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do {
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computed = false
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// compute can happen only in 1 thread but no reason to lock others.
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if (computing.compareAndSet(false, true)) {
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// as long as it is invalid, keep computing.
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try {
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var value: T? = null
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var once = true;
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var last = android.os.SystemClock.elapsedRealtime()
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while (invalid.compareAndSet(true, false)) {
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var now = android.os.SystemClock.elapsedRealtime()
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if (value != null && (once || last + 2500 < now)) {
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eu.faircode.email.Log.i(liveData.toString() + " post once=" + once + " age=" + (now - last) + " ms")
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once = false;
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last = now;
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liveData.postValue(value);
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}
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computed = true
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value = compute()
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}
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if (computed) {
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liveData.postValue(value)
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}
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} catch (ex: Throwable) {
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// java.lang.IllegalStateException: Couldn't read row xxx column yyy
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eu.faircode.email.Log.e(ex);
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invalid.set(true);
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} finally {
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// release compute lock
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computing.set(false)
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}
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}
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// check invalid after releasing compute lock to avoid the following scenario.
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// Thread A runs compute()
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// Thread A checks invalid, it is false
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// Main thread sets invalid to true
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// Thread B runs, fails to acquire compute lock and skips
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// Thread A releases compute lock
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// We've left invalid in set state. The check below recovers.
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} while (computed && invalid.get())
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}
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// invalidation check always happens on the main thread
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@JvmField
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@VisibleForTesting
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internal val invalidationRunnable = Runnable {
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val isActive = liveData.hasActiveObservers()
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if (invalid.compareAndSet(false, true)) {
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if (isActive) {
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executor.execute(refreshRunnable)
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}
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}
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}
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/**
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* Invalidates the LiveData.
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*
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* When there are active observers, this will trigger a call to [.compute].
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*/
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open fun invalidate() {
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ArchTaskExecutor.getInstance().executeOnMainThread(invalidationRunnable)
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}
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// TODO https://issuetracker.google.com/issues/112197238
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@WorkerThread
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protected abstract fun compute(): T
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} |