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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift Async Algorithms open source project
//
// Copyright (c) 2021 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
//
//===----------------------------------------------------------------------===//
extension AsyncSequence {
/// Create a rate-limited `AsyncSequence` by emitting values at most every specified interval.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public func _throttle<C: Clock, Reduced>(for interval: C.Instant.Duration, clock: C, reducing: @Sendable @escaping (Reduced?, Element) async -> Reduced) -> _AsyncThrottleSequence<Self, C, Reduced> {
_AsyncThrottleSequence(self, interval: interval, clock: clock, reducing: reducing)
}
/// Create a rate-limited `AsyncSequence` by emitting values at most every specified interval.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public func _throttle<Reduced>(for interval: Duration, reducing: @Sendable @escaping (Reduced?, Element) async -> Reduced) -> _AsyncThrottleSequence<Self, ContinuousClock, Reduced> {
_throttle(for: interval, clock: .continuous, reducing: reducing)
}
/// Create a rate-limited `AsyncSequence` by emitting values at most every specified interval.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public func _throttle<C: Clock>(for interval: C.Instant.Duration, clock: C, latest: Bool = true) -> _AsyncThrottleSequence<Self, C, Element> {
_throttle(for: interval, clock: clock) { previous, element in
if latest {
return element
} else {
return previous ?? element
}
}
}
/// Create a rate-limited `AsyncSequence` by emitting values at most every specified interval.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public func _throttle(for interval: Duration, latest: Bool = true) -> _AsyncThrottleSequence<Self, ContinuousClock, Element> {
_throttle(for: interval, clock: .continuous, latest: latest)
}
}
/// A rate-limited `AsyncSequence` by emitting values at most every specified interval.
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
public struct _AsyncThrottleSequence<Base: AsyncSequence, C: Clock, Reduced> {
let base: Base
let interval: C.Instant.Duration
let clock: C
let reducing: @Sendable (Reduced?, Base.Element) async -> Reduced
init(_ base: Base, interval: C.Instant.Duration, clock: C, reducing: @Sendable @escaping (Reduced?, Base.Element) async -> Reduced) {
self.base = base
self.interval = interval
self.clock = clock
self.reducing = reducing
}
}
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
extension _AsyncThrottleSequence: AsyncSequence {
public typealias Element = Reduced
/// The iterator for an `AsyncThrottleSequence` instance.
public struct Iterator: AsyncIteratorProtocol {
var base: Base.AsyncIterator
var last: C.Instant?
let interval: C.Instant.Duration
let clock: C
let reducing: @Sendable (Reduced?, Base.Element) async -> Reduced
init(_ base: Base.AsyncIterator, interval: C.Instant.Duration, clock: C, reducing: @Sendable @escaping (Reduced?, Base.Element) async -> Reduced) {
self.base = base
self.interval = interval
self.clock = clock
self.reducing = reducing
}
public mutating func next() async rethrows -> Reduced? {
var reduced: Reduced?
let start = last ?? clock.now
repeat {
guard let element = try await base.next() else {
if reduced != nil, let last {
// ensure the rate of elements never exceeds the given interval
let amount = interval - last.duration(to: clock.now)
if amount > .zero {
try? await clock.sleep(until: clock.now.advanced(by: amount), tolerance: nil)
}
}
// the last value is unable to have any subsequent
// values so always return the last reduction
return reduced
}
let reduction = await reducing(reduced, element)
let now = clock.now
if start.duration(to: now) >= interval || last == nil {
last = now
return reduction
} else {
reduced = reduction
}
} while true
}
}
public func makeAsyncIterator() -> Iterator {
Iterator(base.makeAsyncIterator(), interval: interval, clock: clock, reducing: reducing)
}
}
@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
extension _AsyncThrottleSequence: Sendable where Base: Sendable, Element: Sendable { }
@available(*, unavailable)
extension _AsyncThrottleSequence.Iterator: Sendable { }
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