reactor.core.publisher.DrainUtils Maven / Gradle / Ivy
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/*
* Copyright (c) 2016-2021 VMware Inc. or its affiliates, All Rights Reserved.
*
* 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
*
* https://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 reactor.core.publisher;
import java.util.Queue;
import java.util.concurrent.atomic.AtomicLongFieldUpdater;
import java.util.function.BooleanSupplier;
import org.reactivestreams.Subscriber;
import reactor.core.CoreSubscriber;
import reactor.util.annotation.Nullable;
abstract class DrainUtils {
/**
* Indicates the source completed and the value field is ready to be emitted.
*
* The AtomicLong (this) holds the requested amount in bits 0..62 so there is room
* for one signal bit. This also means the standard request accounting helper method doesn't work.
*/
static final long COMPLETED_MASK = 0x8000_0000_0000_0000L;
static final long REQUESTED_MASK = 0x7FFF_FFFF_FFFF_FFFFL;
/**
* Perform a potential post-completion request accounting.
*
* @param the output value type
* @param the field type holding the requested amount
* @param n the requested amount
* @param actual the consumer of values
* @param queue the queue holding the available values
* @param field the field updater for the requested amount
* @param instance the parent instance for the requested field
* @param isCancelled callback to detect cancellation
* @return true if the state indicates a completion state.
*/
static boolean postCompleteRequest(long n,
Subscriber actual,
Queue queue,
AtomicLongFieldUpdater field,
F instance,
BooleanSupplier isCancelled) {
for (; ; ) {
long r = field.get(instance);
// extract the current request amount
long r0 = r & REQUESTED_MASK;
// preserve COMPLETED_MASK and calculate new requested amount
long u = (r & COMPLETED_MASK) | Operators.addCap(r0, n);
if (field.compareAndSet(instance, r, u)) {
// (complete, 0) -> (complete, n) transition then replay
if (r == COMPLETED_MASK) {
postCompleteDrain(n | COMPLETED_MASK, actual, queue, field, instance, isCancelled);
return true;
}
// (active, r) -> (active, r + n) transition then continue with requesting from upstream
return false;
}
}
}
/**
* Drains the queue either in a pre- or post-complete state.
*
* @param n the requested amount
* @param actual the consumer of values
* @param queue the queue holding available values
* @param field the field updater holding the requested amount
* @param instance the parent instance of the requested field
* @param isCancelled callback to detect cancellation
* @return true if the queue was completely drained or the drain process was cancelled
*/
static boolean postCompleteDrain(long n,
Subscriber actual,
Queue queue,
AtomicLongFieldUpdater field,
F instance,
BooleanSupplier isCancelled) {
// TODO enable fast-path
// if (n == -1 || n == Long.MAX_VALUE) {
// for (;;) {
// if (isDisposed.getAsBoolean()) {
// break;
// }
//
// T v = queue.poll();
//
// if (v == null) {
// actual.onComplete();
// break;
// }
//
// actual.onNext(v);
// }
//
// return true;
// }
long e = n & COMPLETED_MASK;
for (; ; ) {
while (e != n) {
if (isCancelled.getAsBoolean()) {
return true;
}
T t = queue.poll();
if (t == null) {
actual.onComplete();
return true;
}
actual.onNext(t);
e++;
}
if (isCancelled.getAsBoolean()) {
return true;
}
if (queue.isEmpty()) {
actual.onComplete();
return true;
}
n = field.get(instance);
if (n == e) {
n = field.addAndGet(instance, -(e & REQUESTED_MASK));
if ((n & REQUESTED_MASK) == 0L) {
return false;
}
e = n & COMPLETED_MASK;
}
}
}
/**
* Tries draining the queue if the source just completed.
*
* @param the output value type
* @param the field type holding the requested amount
* @param actual the consumer of values
* @param queue the queue holding available values
* @param field the field updater holding the requested amount
* @param instance the parent instance of the requested field
* @param isCancelled callback to detect cancellation
*/
public static void postComplete(CoreSubscriber actual,
Queue queue,
AtomicLongFieldUpdater field,
F instance,
BooleanSupplier isCancelled) {
if (queue.isEmpty()) {
actual.onComplete();
return;
}
if (postCompleteDrain(field.get(instance), actual, queue, field, instance, isCancelled)) {
return;
}
for (; ; ) {
long r = field.get(instance);
if ((r & COMPLETED_MASK) != 0L) {
return;
}
long u = r | COMPLETED_MASK;
// (active, r) -> (complete, r) transition
if (field.compareAndSet(instance, r, u)) {
// if the requested amount was non-zero, drain the queue
if (r != 0L) {
postCompleteDrain(u, actual, queue, field, instance, isCancelled);
}
return;
}
}
}
/**
* Perform a potential post-completion request accounting.
*
* @param the output value type
* @param the field type holding the requested amount
* @param n the request amount
* @param actual the consumer of values
* @param queue the queue of available values
* @param field the field updater for the requested amount
* @param instance the parent instance of the requested field
* @param isCancelled callback to detect cancellation
* @param error if not null, the error to signal after the queue has been drained
* @return true if the state indicates a completion state.
*/
public static boolean postCompleteRequestDelayError(long n,
Subscriber actual,
Queue queue,
AtomicLongFieldUpdater field,
F instance,
BooleanSupplier isCancelled, Throwable error) {
for (; ; ) {
long r = field.get(instance);
// extract the current request amount
long r0 = r & REQUESTED_MASK;
// preserve COMPLETED_MASK and calculate new requested amount
long u = (r & COMPLETED_MASK) | Operators.addCap(r0, n);
if (field.compareAndSet(instance, r, u)) {
// (complete, 0) -> (complete, n) transition then replay
if (r == COMPLETED_MASK) {
postCompleteDrainDelayError(n | COMPLETED_MASK, actual, queue, field, instance, isCancelled, error);
return true;
}
// (active, r) -> (active, r + n) transition then continue with requesting from upstream
return false;
}
}
}
/**
* Drains the queue either in a pre- or post-complete state, delaying an
* optional error to the end of the drain operation.
*
* @param n the requested amount
* @param actual the consumer of values
* @param queue the queue holding available values
* @param field the field updater holding the requested amount
* @param instance the parent instance of the requested field
* @param isCancelled callback to detect cancellation
* @param error the delayed error
* @return true if the queue was completely drained or the drain process was cancelled
*/
static boolean postCompleteDrainDelayError(long n,
Subscriber actual,
Queue queue,
AtomicLongFieldUpdater field,
F instance,
BooleanSupplier isCancelled,
@Nullable Throwable error) {
long e = n & COMPLETED_MASK;
for (; ; ) {
while (e != n) {
if (isCancelled.getAsBoolean()) {
return true;
}
T t = queue.poll();
if (t == null) {
if (error == null) {
actual.onComplete();
} else {
actual.onError(error);
}
return true;
}
actual.onNext(t);
e++;
}
if (isCancelled.getAsBoolean()) {
return true;
}
if (queue.isEmpty()) {
if (error == null) {
actual.onComplete();
} else {
actual.onError(error);
}
return true;
}
n = field.get(instance);
if (n == e) {
n = field.addAndGet(instance, -(e & REQUESTED_MASK));
if ((n & REQUESTED_MASK) == 0L) {
return false;
}
e = n & COMPLETED_MASK;
}
}
}
/**
* Tries draining the queue if the source just completed.
*
* @param the output value type
* @param the field type holding the requested amount
* @param actual the consumer of values
* @param queue the queue of available values
* @param field the field updater for the requested amount
* @param instance the parent instance of the requested field
* @param isCancelled callback to detect cancellation
* @param error if not null, the error to signal after the queue has been drained
*/
public static void postCompleteDelayError(CoreSubscriber actual,
Queue queue,
AtomicLongFieldUpdater field,
F instance,
BooleanSupplier isCancelled,
@Nullable Throwable error) {
if (queue.isEmpty()) {
if (error == null) {
actual.onComplete();
} else {
actual.onError(error);
}
return;
}
if (postCompleteDrainDelayError(field.get(instance), actual, queue, field, instance, isCancelled, error)) {
return;
}
for (; ; ) {
long r = field.get(instance);
if ((r & COMPLETED_MASK) != 0L) {
return;
}
long u = r | COMPLETED_MASK;
// (active, r) -> (complete, r) transition
if (field.compareAndSet(instance, r, u)) {
// if the requested amount was non-zero, drain the queue
if (r != 0L) {
postCompleteDrainDelayError(u, actual, queue, field, instance, isCancelled, error);
}
return;
}
}
}
DrainUtils(){}
}