/*
* Copyright 2000-2016 JetBrains s.r.o.
*
* 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 org.jetbrains.concurrency;
import com.intellij.openapi.util.Getter;
import com.intellij.util.concurrency.AtomicFieldUpdater;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
public abstract class PromiseManager<HOST, VALUE> {
private final AtomicFieldUpdater<HOST, Promise<VALUE>> fieldUpdater;
@SuppressWarnings("UnusedDeclaration")
public PromiseManager(@NotNull AtomicFieldUpdater<HOST, Promise<VALUE>> fieldUpdater) {
this.fieldUpdater = fieldUpdater;
}
public PromiseManager(@NotNull Class<HOST> ownerClass) {
//noinspection unchecked
fieldUpdater = ((AtomicFieldUpdater)AtomicFieldUpdater.forFieldOfType(ownerClass, Promise.class));
}
public boolean isUpToDate(@NotNull HOST host, @NotNull VALUE value) {
return true;
}
@NotNull
public abstract Promise<VALUE> load(@NotNull HOST host);
public final void reset(HOST host) {
fieldUpdater.set(host, null);
}
public final void set(HOST host, @Nullable VALUE value) {
if (value == null) {
reset(host);
}
else {
((AsyncPromise<VALUE>)getOrCreateAsyncResult(host, false, false)).setResult(value);
}
}
public final boolean has(HOST host) {
Promise<VALUE> result = fieldUpdater.get(host);
return result != null && result.getState() == Promise.State.FULFILLED;
}
@Nullable
public final Promise.State getState(HOST host) {
Promise<VALUE> result = fieldUpdater.get(host);
return result == null ? null : result.getState();
}
@NotNull
public final Promise<VALUE> get(HOST host) {
return get(host, true);
}
@NotNull
public final Promise<VALUE> get(HOST host, boolean checkFreshness) {
return getOrCreateAsyncResult(host, checkFreshness, true);
}
@NotNull
private Promise<VALUE> getOrCreateAsyncResult(HOST host, boolean checkFreshness, boolean load) {
Promise<VALUE> promise = fieldUpdater.get(host);
if (promise == null) {
if (!fieldUpdater.compareAndSet(host, null, promise = new AsyncPromise<>())) {
return fieldUpdater.get(host);
}
}
else {
Promise.State state = promise.getState();
if (state == Promise.State.PENDING) {
// if current promise is not processed, so, we don't need to check cache state
return promise;
}
else if (state == Promise.State.FULFILLED) {
//noinspection unchecked
if (!checkFreshness || isUpToDate(host, ((Getter<VALUE>)promise).get())) {
return promise;
}
if (!fieldUpdater.compareAndSet(host, promise, promise = new AsyncPromise<>())) {
Promise<VALUE> valueFromAnotherThread = fieldUpdater.get(host);
while (valueFromAnotherThread == null) {
if (fieldUpdater.compareAndSet(host, null, promise)) {
return getPromise(host, load, promise);
}
else {
valueFromAnotherThread = fieldUpdater.get(host);
}
}
return valueFromAnotherThread;
}
}
}
return getPromise(host, load, promise);
}
@NotNull
private Promise<VALUE> getPromise(HOST host, boolean load, Promise<VALUE> promise) {
if (!load || promise.getState() != Promise.State.PENDING) {
return promise;
}
Promise<VALUE> effectivePromise = load(host);
if (effectivePromise != promise) {
fieldUpdater.compareAndSet(host, promise, effectivePromise);
effectivePromise.notify((AsyncPromise<VALUE>)promise);
}
return effectivePromise;
}
}