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//===----------------------------------------------------------------------===//
//
// This source file is part of the SwiftNIO open source project
//
// Copyright (c) 2022 Apple Inc. and the SwiftNIO project authors
// Licensed under Apache License v2.0
//
// See LICENSE.txt for license information
// See CONTRIBUTORS.txt for the list of SwiftNIO project authors
//
// SPDX-License-Identifier: Apache-2.0
//
//===----------------------------------------------------------------------===//
public enum NIOAsyncSequenceProducerBackPressureStrategies {
/// A high-low watermarked back-pressure strategy for a ``NIOAsyncSequenceProducer``.
///
/// This strategy does the following:
/// - On yield it keeps on demanding more elements from the producer as long as the number of buffered elements hasn't reached the `highWatermark`.
/// - On consume it starts to demand again from the producer once the number of buffered elements reach the `lowWatermark`.
@available(macOS 10.15, iOS 13, tvOS 13, watchOS 6, *)
public struct HighLowWatermark: NIOAsyncSequenceProducerBackPressureStrategy {
private let lowWatermark: Int
private let highWatermark: Int
/// Initializes a new ``NIOAsyncSequenceProducerBackPressureStrategies/HighLowWatermark``.
///
/// - Parameters:
/// - lowWatermark: The low watermark where demand should start.
/// - highWatermark: The high watermark where demand should be stopped.
public init(lowWatermark: Int, highWatermark: Int) {
precondition(lowWatermark <= highWatermark)
self.lowWatermark = lowWatermark
self.highWatermark = highWatermark
}
public mutating func didYield(bufferDepth: Int) -> Bool {
// We are demanding more until we reach the high watermark
bufferDepth < self.highWatermark
}
public mutating func didConsume(bufferDepth: Int) -> Bool {
// We start demanding again once we are below the low watermark
bufferDepth < self.lowWatermark
}
}
}
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