57 lines
1.4 KiB
Swift
57 lines
1.4 KiB
Swift
//
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// OnceContinuation.swift
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// Tun
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//
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// Created by Codex on 2026/5/7.
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//
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import Foundation
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final class OnceContinuation<Value, Failure: Error>: @unchecked Sendable {
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private let lock = NSLock()
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private var continuation: CheckedContinuation<Value, Failure>?
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private var result: Result<Value, Failure>?
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func set(_ continuation: CheckedContinuation<Value, Failure>) {
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lock.lock()
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if let result {
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lock.unlock()
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continuation.resume(with: result)
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return
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}
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let hasPendingContinuation = self.continuation != nil
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if !hasPendingContinuation {
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self.continuation = continuation
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}
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lock.unlock()
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if hasPendingContinuation {
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preconditionFailure("OnceContinuation can only store one pending continuation")
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}
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}
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func resume(returning value: Value) {
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resume(with: .success(value))
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}
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func resume(throwing error: Failure) {
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resume(with: .failure(error))
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}
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func resume(with result: Result<Value, Failure>) {
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lock.lock()
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guard self.result == nil else {
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lock.unlock()
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return
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}
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self.result = result
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let continuation = self.continuation
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self.continuation = nil
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lock.unlock()
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continuation?.resume(with: result)
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}
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}
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