101 lines
2.8 KiB
C++
101 lines
2.8 KiB
C++
// Copyright (c) Facebook, Inc. and its affiliates.
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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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#pragma once
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#include <atomic>
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#include <cstdint>
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#include <limits>
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#include <stdexcept>
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namespace yarpl {
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namespace credits {
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constexpr int64_t kCanceled{std::numeric_limits<int64_t>::min()};
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constexpr int64_t kNoFlowControl{std::numeric_limits<int64_t>::max()};
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/**
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* Utility functions to help with handling request(int64_t n) since it can be
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* called concurrently and must handle rollover.
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*
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* Since Flowable Subscription must have an int64_t per Subscription, we also
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* leverage it for storing cancellation by setting to INT64_MIN so we don't have
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* to also deal with a separate boolean field per Subscription.
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*
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* These functions are thread-safe and intended to deal with concurrent
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* modification by all working off of std::atomic and using
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* compare_exchange_strong.
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*/
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/**
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* Add the new value 'n' to the 'current' atomic<int64_t>.
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*
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* Caps the result at INT64_MAX.
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*
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* Adding a negative number does nothing.
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*
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* If 'current' is set to "cancelled" using the magic number INT64_MIN it will
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* not be changed.
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*
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* Returns new value of credits.
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*/
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int64_t add(std::atomic<int64_t>*, int64_t);
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/**
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* Version of add that works for non-atomic integers.
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*/
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int64_t add(int64_t, int64_t);
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/**
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* Set 'current' to INT64_MIN as a magic number to represent "cancelled".
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*
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* Return true if this changed to cancelled, or false if it was already
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* cancelled.
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*/
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bool cancel(std::atomic<int64_t>*);
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/**
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* Consume (remove) credits from the 'current' atomic<int64_t>.
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*
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* This MUST only be used to remove credits after emitting a value via onNext.
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*
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* Returns new value of credits.
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*/
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int64_t consume(std::atomic<int64_t>*, int64_t);
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/**
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* Try Consume (remove) credits from the 'current' atomic<int64_t>.
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*
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* Returns true if consuming the credit was successful.
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*/
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bool tryConsume(std::atomic<int64_t>*, int64_t);
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/**
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* Version of consume that works for non-atomic integers.
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*/
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int64_t consume(int64_t&, int64_t);
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/**
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* Whether the current value represents a "cancelled" subscription.
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*/
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bool isCancelled(std::atomic<int64_t>*);
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/**
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* If the requested value is MAX so we can ignore flow control.
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*/
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bool isInfinite(std::atomic<int64_t>*);
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} // namespace credits
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} // namespace yarpl
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