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//===----------------------------------------------------------------------===//
//
// This source file is part of the Swift open source project
//
// Copyright (c) 2025 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
/// An object which allows unstructured tracking of an asynchronous operation, whose completion can be signaled from synchronous code.
///
/// - note: While this has a similar API surface as `DispatchSemaphore`, the semantics are different in that `signal()` and `wait()` are idempotent.
public final class WaitCondition: Sendable {
private let promise = Promise<Void, Never>()
public init() {
}
/// Signals completion of the condition.
///
/// - note: This function is idempotent.
public func signal() {
_ = promise.fulfill()
}
/// Asynchronously waits for the condition to complete. Continues waiting even if the current task is cancelled.
///
/// - note: This function is idempotent. If the condition is already completed, the function returns immediately.
public func wait() async {
await promise.value
}
}
/// An object which allows unstructured tracking of an asynchronous operation, whose completion can be signaled from synchronous code.
///
/// - note: While this has a similar API surface as `DispatchSemaphore`, the semantics are different in that `signal()` and `wait()` are idempotent.
public final class CancellableWaitCondition: Sendable {
private let promise = Promise<Void, any Error>()
public init() {
}
/// Cancels the wait condition. If the condition has already succeeded, does nothing.
///
/// - note: This function is idempotent.
public func cancel() {
_ = promise.fail(throwing: CancellationError())
}
/// Signals completion of the condition.
///
/// - note: This function is idempotent.
public func signal() {
_ = promise.fulfill()
}
/// Asynchronously waits for the condition to complete.
///
/// - throws: ``CancellationError`` if the current task was cancelled.
/// - note: This function is idempotent. If the condition is already completed, the function returns immediately.
public func wait() async throws {
try await withTaskCancellationHandler {
try await promise.value
} onCancel: {
cancel()
}
}
}
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