com.abubusoft.kripton.androidx.livedata.KriptonXPagedLiveDataHandlerImpl Maven / Gradle / Ivy
Show all versions of kripton-android-core Show documentation
/*
* Copyright (C) 2017 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 com.abubusoft.kripton.androidx.livedata;
import java.util.concurrent.atomic.AtomicBoolean;
import com.abubusoft.kripton.android.LiveDataHandler;
import com.abubusoft.kripton.android.PageRequest;
import com.abubusoft.kripton.android.PagedResult;
import com.abubusoft.kripton.android.executor.KriptonTaskExecutor;
import android.support.annotation.MainThread;
import android.support.annotation.NonNull;
import android.support.annotation.VisibleForTesting;
import android.support.annotation.WorkerThread;
/**
* A PLiveData class that can be invalidated and computed on demand.
*
* This is an internal class for now, might be public if we see the necessity.
*
* @param
* The type of the live data
*/
public abstract class KriptonXPagedLiveDataHandlerImpl implements LiveDataHandler {
/** The m live data. */
private final PagedLiveData mLiveData;
/** The m invalid. */
private AtomicBoolean mInvalid = new AtomicBoolean(true);
/** The m computing. */
private AtomicBoolean mComputing = new AtomicBoolean(false);
/**
* Creates a computable live data which is computed when there are active
* observers.
*
* It can also be invalidated via {@link #invalidate()} which will result in
* a call to {@link #compute()} if there are active observers (or when they
* start observing)
*/
public KriptonXPagedLiveDataHandlerImpl(PagedResult pagedResult) {
mLiveData = new PagedLiveData(pagedResult, this) {
@Override
protected void onActive() {
KriptonTaskExecutor.getInstance().executeOnDiskIO(mRefreshRunnable);
}
};
}
/**
* Returns the LiveData managed by this class.
*
* @return A LiveData that is controlled by ComputableLiveData.
*/
@NonNull
public PagedLiveData getLiveData() {
return mLiveData;
}
/** The m refresh runnable. */
@VisibleForTesting
final Runnable mRefreshRunnable = new Runnable() {
@WorkerThread
@Override
public void run() {
boolean computed;
do {
computed = false;
// compute can happen only in 1 thread but no reason to lock
// others.
if (mComputing.compareAndSet(false, true)) {
// as long as it is invalid, keep computing.
try {
T value = null;
while (mInvalid.compareAndSet(true, false)) {
computed = true;
value = compute();
}
if (computed) {
mLiveData.updateValue(value);
// mLiveData.postValue(value);
}
} finally {
// release compute lock
mComputing.set(false);
}
}
// check invalid after releasing compute lock to avoid the
// following scenario.
// Thread A runs compute()
// Thread A checks invalid, it is false
// Main thread sets invalid to true
// Thread B runs, fails to acquire compute lock and skips
// Thread A releases compute lock
// We've left invalid in set state. The check below recovers.
} while (computed && mInvalid.get());
}
};
/** The m invalidation runnable. */
// invalidation check always happens on the main thread
@VisibleForTesting
final Runnable mInvalidationRunnable = new Runnable() {
@MainThread
@Override
public void run() {
boolean isActive = mLiveData.hasActiveObservers();
if (mInvalid.compareAndSet(false, true)) {
if (isActive) {
KriptonTaskExecutor.getInstance().executeOnDiskIO(mRefreshRunnable);
}
}
}
};
/**
* Invalidates the LiveData.
*
* When there are active observers, this will trigger a call to
* {@link #compute()}.
*/
@Override
public void invalidate() {
KriptonTaskExecutor.getInstance().executeOnMainThread(mInvalidationRunnable);
}
/**
* Compute.
*
* @return the t
*/
@WorkerThread
protected abstract T compute();
}