/*
* Copyright (c) Meta Platforms, Inc. and affiliates.
*
* 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.
*/
#pragma once
#include <folly/channels/Channel.h>
#include <folly/container/F14Set.h>
#include <folly/executors/SequencedExecutor.h>
#include <folly/experimental/channels/detail/Utility.h>
namespace folly {
namespace channels {
namespace detail {
template <typename ValueType>
class FanoutSenderProcessor : public IChannelCallback {
private:
struct State {
folly::F14FastSet<ChannelBridge<ValueType>*> senders_;
bool handleDestroyed_{false};
};
using WLockedStatePtr = typename folly::Synchronized<State>::WLockedPtr;
public:
/**
* Subscribes with an already-created sender.
*/
void addSender(detail::ChannelBridgePtr<ValueType> sender) {
auto state = state_.wlock();
sender->senderWait(this);
state->senders_.insert(sender.release());
}
/**
* Sends the given value to all corresponding receivers.
*/
template <typename U = ValueType>
void write(U&& element) {
auto state = state_.wlock();
for (auto* sender : state->senders_) {
sender->senderPush(element);
}
}
/**
* This is called when the user's FanoutSender object has been destroyed.
*/
void destroyHandle(CloseResult closeResult) {
processHandleDestroyed(state_.wlock(), std::move(closeResult));
}
/**
* Returns whether this fanout channel has any output receivers.
*/
size_t numSubscribers() const { return state_.rlock()->senders_.size(); }
std::pair<bool, ChannelBridgePtr<ValueType>>
stealSenderAndDestorySelfIfSingle() {
auto state = state_.wlock();
if (state->senders_.empty()) {
// There are no remaining senders. We will destroy ourselves.
state->handleDestroyed_ = true;
maybeDelete(std::move(state));
return std::make_pair(true, ChannelBridgePtr<ValueType>());
} else if (state->senders_.size() == 1) {
// There is one remaining sender.
auto* sender = *state->senders_.begin();
auto* callback = sender->cancelSenderWait();
if (callback) {
// We successfully cancelled the callback, so we can now destroy
// ourselves and return the sender.
state->senders_.clear();
state->handleDestroyed_ = true;
maybeDelete(std::move(state));
return std::make_pair(true, ChannelBridgePtr<ValueType>(sender));
} else {
// We failed to cancel the callback. This means that another thread is
// invoking the callback by calling consume(), letting us know that the
// corresponding receiver was deleted. The callback will start running
// once we release the lock, so we will let the callback delete the
// sender (and then destroy ourselves).
return std::make_pair(true, ChannelBridgePtr<ValueType>());
}
} else {
// There is more than one sender. Do not destroy ourselves.
return std::make_pair(false, ChannelBridgePtr<ValueType>());
}
}
static ChannelState getSenderState(ChannelBridge<ValueType>* sender) {
return detail::getSenderState(sender);
}
private:
/**
* Called when receiving a cancellation from an output receiver.
*/
void consume(ChannelBridgeBase* bridge) override {
// The consumer of an output receiver has stopped consuming.
auto state = state_.wlock();
auto* sender = static_cast<ChannelBridge<ValueType>*>(bridge);
CHECK_NE(getSenderState(sender), ChannelState::CancellationProcessed);
sender->senderClose();
processSenderCancelled(std::move(state), sender);
}
void canceled(ChannelBridgeBase*) override {
// We cancel the callback before we close the sender explicitly, so this
// should never be hit.
CHECK(false);
}
/**
* Processes the cancellation of a sender (indicating that the consumer of
* the corresponding output receiver has stopped consuming).
*/
void processSenderCancelled(
WLockedStatePtr state, ChannelBridge<ValueType>* sender) {
CHECK_EQ(getSenderState(sender), ChannelState::CancellationTriggered);
state->senders_.erase(sender);
deleteSender(sender);
maybeDelete(std::move(state));
}
/**
* Processes the destruction of the user's FanoutChannel object. We will
* cancel the receiver and trigger cancellation for all senders not already
* cancelled.
*/
void processHandleDestroyed(WLockedStatePtr state, CloseResult closeResult) {
CHECK(!state->handleDestroyed_);
state->handleDestroyed_ = true;
auto senders = state->senders_;
for (auto* sender : senders) {
auto* callback = sender->cancelSenderWait();
if (closeResult.exception.has_value()) {
sender->senderClose(closeResult.exception.value());
} else {
sender->senderClose();
}
if (callback) {
// We successfully cancelled the callback, so we can now delete the
// sender.
CHECK_EQ(callback, this);
state->senders_.erase(sender);
deleteSender(sender);
} else {
// We failed to cancel the callback. This means that another thread is
// invoking the callback by calling consume(), letting us know that the
// corresponding receiver was deleted. The callback will start running
// once we release the lock, so we will let the callback delete the
// sender.
}
}
maybeDelete(std::move(state));
}
/*
* Deletes the given sender.
*/
void deleteSender(ChannelBridge<ValueType>* sender) {
(ChannelBridgePtr<ValueType>(sender));
}
/**
* Deletes this object if we have already processed cancellation for the
* receiver and all senders, and if the user's FanoutChannel object was
* destroyed.
*/
void maybeDelete(WLockedStatePtr state) {
if (state->senders_.empty() && state->handleDestroyed_) {
state.unlock();
delete this;
}
}
folly::Synchronized<State> state_;
};
} // namespace detail
template <typename ValueType>
FanoutSender<ValueType>::FanoutSender()
: senders_(static_cast<detail::ChannelBridge<ValueType>*>(nullptr)) {}
template <typename ValueType>
FanoutSender<ValueType>::FanoutSender(FanoutSender&& other) noexcept
: senders_(std::move(other.senders_)) {}
template <typename ValueType>
FanoutSender<ValueType>& FanoutSender<ValueType>::operator=(
FanoutSender&& other) noexcept {
if (&other == this) {
return *this;
}
std::move(*this).close();
senders_ = std::move(senders_);
return *this;
}
template <typename ValueType>
FanoutSender<ValueType>::~FanoutSender() {
std::move(*this).close();
}
template <typename ValueType>
Receiver<ValueType> FanoutSender<ValueType>::subscribe(
std::vector<ValueType> initialValues) {
auto [newReceiver, newSender] = Channel<ValueType>::create();
for (auto&& initialValue : initialValues) {
newSender.write(std::move(initialValue));
}
subscribe(std::move(newSender));
return std::move(newReceiver);
}
template <typename ValueType>
void FanoutSender<ValueType>::subscribe(Sender<ValueType> newSender) {
clearSendersWithClosedReceivers();
if (!anySubscribersImpl()) {
// There are currently no output receivers. Store the new output receiver.
senders_.set(detail::senderGetBridge(newSender).release());
} else if (!hasProcessor()) {
// There is currently exactly one output receiver. Convert to a processor.
auto* processor = new detail::FanoutSenderProcessor<ValueType>();
processor->addSender(
detail::ChannelBridgePtr<ValueType>(getSingleSender()));
processor->addSender(std::move(detail::senderGetBridge(newSender)));
senders_.set(processor);
} else {
// There are currently more than one output receivers. Add the new receiver
// to the existing processor.
auto* processor = getProcessor();
processor->addSender(std::move(detail::senderGetBridge(newSender)));
}
}
template <typename ValueType>
bool FanoutSender<ValueType>::anySubscribers() const {
clearSendersWithClosedReceivers();
return anySubscribersImpl();
}
template <typename ValueType>
std::uint64_t FanoutSender<ValueType>::numSubscribers() const {
clearSendersWithClosedReceivers();
if (!anySubscribersImpl()) {
return 0;
} else if (!hasProcessor()) {
return 1;
} else {
return getProcessor()->numSubscribers();
}
}
template <typename ValueType>
template <typename U>
void FanoutSender<ValueType>::write(U&& element) {
clearSendersWithClosedReceivers();
if (!anySubscribersImpl()) {
// There are currently no output receivers to write to.
return;
} else if (!hasProcessor()) {
// There is exactly one output receiver. Write the value to that receiver.
getSingleSender()->senderPush(std::forward<U>(element));
} else {
getProcessor()->write(std::forward<U>(element));
}
}
template <typename ValueType>
void FanoutSender<ValueType>::close(exception_wrapper ex) && {
clearSendersWithClosedReceivers();
if (!anySubscribersImpl()) {
// There are no output receivers to close.
return;
} else if (!hasProcessor()) {
// There is exactly one output receiver to close.
if (ex) {
getSingleSender()->senderClose(ex);
} else {
getSingleSender()->senderClose();
}
// Delete the output receiver.
(detail::ChannelBridgePtr<ValueType>(getSingleSender()));
senders_.set(static_cast<detail::ChannelBridge<ValueType>*>(nullptr));
} else {
// There is more than one output receiver to close.
getProcessor()->destroyHandle(
ex ? detail::CloseResult(std::move(ex)) : detail::CloseResult());
senders_.set(static_cast<detail::ChannelBridge<ValueType>*>(nullptr));
}
}
template <typename ValueType>
bool FanoutSender<ValueType>::anySubscribersImpl() const {
return hasProcessor() || getSingleSender() != nullptr;
}
template <typename ValueType>
bool FanoutSender<ValueType>::hasProcessor() const {
return senders_.index() == 1;
}
template <typename ValueType>
detail::ChannelBridge<ValueType>* FanoutSender<ValueType>::getSingleSender()
const {
return senders_.get(folly::tag_t<detail::ChannelBridge<ValueType>>{});
}
template <typename ValueType>
detail::FanoutSenderProcessor<ValueType>*
FanoutSender<ValueType>::getProcessor() const {
return senders_.get(folly::tag_t<detail::FanoutSenderProcessor<ValueType>>{});
}
template <typename ValueType>
void FanoutSender<ValueType>::clearSendersWithClosedReceivers() const {
if (hasProcessor()) {
auto [processorDestroyed, remainingSender] =
getProcessor()->stealSenderAndDestorySelfIfSingle();
if (processorDestroyed) {
if (remainingSender) {
senders_.set(remainingSender.release());
} else {
senders_.set(static_cast<detail::ChannelBridge<ValueType>*>(nullptr));
}
}
} else {
auto* bridge = getSingleSender();
if (bridge) {
// There is currently exactly one output receiver. Check to see if it has
// been cancelled.
auto values = bridge->senderGetValues();
if (!values.empty()) {
bridge->senderClose();
senders_.set(static_cast<detail::ChannelBridge<ValueType>*>(nullptr));
// Delete the output receiver.
(detail::ChannelBridgePtr<ValueType>(bridge));
}
}
}
}
} // namespace channels
} // namespace folly
Codebase Browser
folly