67 lines
1.9 KiB
Swift
67 lines
1.9 KiB
Swift
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//
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// Collection.swift
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//
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//
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// Created by MainasuK on 2021-12-7.
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//
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import Foundation
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// https://gist.github.com/DougGregor/92a2e4f6e11f6d733fb5065e9d1c880f
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extension Collection {
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public func parallelMap<T>(
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parallelism requestedParallelism: Int? = nil,
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_ transform: @escaping (Element) async throws -> T
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) async rethrows -> [T] {
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let defaultParallelism = 2
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let parallelism = requestedParallelism ?? defaultParallelism
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let n = count
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if n == 0 {
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return []
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}
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return try await withThrowingTaskGroup(of: (Int, T).self, returning: [T].self) { group in
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var result = [T?](repeatElement(nil, count: n))
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var i = self.startIndex
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var submitted = 0
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func submitNext() async throws {
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if i == self.endIndex { return }
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group.addTask { [submitted, i] in
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let value = try await transform(self[i])
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return (submitted, value)
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}
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submitted += 1
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formIndex(after: &i)
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}
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// submit first initial tasks
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for _ in 0 ..< parallelism {
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try await submitNext()
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}
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// as each task completes, submit a new task until we run out of work
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while let (index, taskResult) = try await group.next() {
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result[index] = taskResult
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try Task.checkCancellation()
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try await submitNext()
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}
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assert(result.count == n)
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return Array(result.compactMap { $0 })
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}
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}
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func parallelEach(
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parallelism requestedParallelism: Int? = nil,
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_ work: @escaping (Element) async throws -> Void
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) async rethrows {
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_ = try await parallelMap {
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try await work($0)
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}
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}
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}
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