feat: Initial implementation of many GCD API's using Swift Concurrency

.github/workflows/pull_request.yml

@@ -0,0 +1,42 @@
+name: Pull request
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize]
+
+jobs:
+  soundness:
+    name: Soundness
+    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
+    with:
+      license_header_check_project_name: "Swift.org"
+      api_breakage_check_enabled: false
+
+  tests:
+    name: tests
+    uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
+    with:
+      enable_macos_checks: false
+      linux_exclude_swift_versions: "[{\"swift_version\": \"5.9\"}, {\"swift_version\": \"5.10\"}, {\"swift_version\": \"5.10.1\"}, {\"swift_version\": \"6.0\"}]"
+      enable_windows_checks: false
+
+  wasm-sdk:
+    name: WebAssembly SDK
+    runs-on: ubuntu-latest
+    container:
+      image: "swift:6.1.0-noble"
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+      - name: Swift version
+        run: swift --version
+      - name: WasmBuild
+        # TODO: Update this to use swift-nio once https://github.com/apple/swift-nio/pull/3159/ is merged
+        run: |
+          apt-get update -y -q
+          apt-get install -y -q curl
+          apt-get install -y -q jq
+          version="$(swift --version | head -n1)"
+          tag="$(curl -sL "https://raw.githubusercontent.com/swiftwasm/swift-sdk-index/refs/heads/main/v1/tag-by-version.json" | jq -e -r --arg v "$version" '.[$v] | .[-1]')"
+          curl -sL "https://raw.githubusercontent.com/swiftwasm/swift-sdk-index/refs/heads/main/v1/builds/$tag.json" | jq -r '.["swift-sdks"]["wasm32-unknown-wasi"] | "swift sdk install \"\(.url)\" --checksum \"\(.checksum)\""' | sh -x
+          swift build --swift-sdk wasm32-unknown-wasi

.gitignore

@@ -1,62 +1,8 @@
-# Xcode
-#
-# gitignore contributors: remember to update Global/Xcode.gitignore, Objective-C.gitignore & Swift.gitignore
-
-## User settings
+.DS_Store
+/.build
+/Packages
 xcuserdata/
-
-## Obj-C/Swift specific
-*.hmap
-
-## App packaging
-*.ipa
-*.dSYM.zip
-*.dSYM
-
-## Playgrounds
-timeline.xctimeline
-playground.xcworkspace
-
-# Swift Package Manager
-#
-# Add this line if you want to avoid checking in source code from Swift Package Manager dependencies.
-# Packages/
-# Package.pins
-# Package.resolved
-# *.xcodeproj
-#
-# Xcode automatically generates this directory with a .xcworkspacedata file and xcuserdata
-# hence it is not needed unless you have added a package configuration file to your project
-# .swiftpm
-
-.build/
-
-# CocoaPods
-#
-# We recommend against adding the Pods directory to your .gitignore. However
-# you should judge for yourself, the pros and cons are mentioned at:
-# https://guides.cocoapods.org/using/using-cocoapods.html#should-i-check-the-pods-directory-into-source-control
-#
-# Pods/
-#
-# Add this line if you want to avoid checking in source code from the Xcode workspace
-# *.xcworkspace
-
-# Carthage
-#
-# Add this line if you want to avoid checking in source code from Carthage dependencies.
-# Carthage/Checkouts
-
-Carthage/Build/
-
-# fastlane
-#
-# It is recommended to not store the screenshots in the git repo.
-# Instead, use fastlane to re-generate the screenshots whenever they are needed.
-# For more information about the recommended setup visit:
-# https://docs.fastlane.tools/best-practices/source-control/#source-control
-
-fastlane/report.xml
-fastlane/Preview.html
-fastlane/screenshots/**/*.png
-fastlane/test_output
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

.licenseignore

@@ -0,0 +1 @@
+Package.swift

.swift-format

@@ -0,0 +1,73 @@
+{
+  "fileScopedDeclarationPrivacy" : {
+    "accessLevel" : "private"
+  },
+  "indentConditionalCompilationBlocks" : false,
+  "indentSwitchCaseLabels" : false,
+  "indentation" : {
+    "spaces" : 4
+  },
+  "lineBreakAroundMultilineExpressionChainComponents" : false,
+  "lineBreakBeforeControlFlowKeywords" : false,
+  "lineBreakBeforeEachArgument" : false,
+  "lineBreakBeforeEachGenericRequirement" : false,
+  "lineBreakBetweenDeclarationAttributes" : false,
+  "lineLength" : 140,
+  "maximumBlankLines" : 1,
+  "multiElementCollectionTrailingCommas" : true,
+  "noAssignmentInExpressions" : {
+    "allowedFunctions" : [
+      "XCTAssertNoThrow"
+    ]
+  },
+  "prioritizeKeepingFunctionOutputTogether" : false,
+  "reflowMultilineStringLiterals" : "never",
+  "respectsExistingLineBreaks" : true,
+  "rules" : {
+    "AllPublicDeclarationsHaveDocumentation" : false,
+    "AlwaysUseLiteralForEmptyCollectionInit" : false,
+    "AlwaysUseLowerCamelCase" : true,
+    "AmbiguousTrailingClosureOverload" : true,
+    "BeginDocumentationCommentWithOneLineSummary" : false,
+    "DoNotUseSemicolons" : true,
+    "DontRepeatTypeInStaticProperties" : true,
+    "FileScopedDeclarationPrivacy" : true,
+    "FullyIndirectEnum" : true,
+    "GroupNumericLiterals" : true,
+    "IdentifiersMustBeASCII" : true,
+    "NeverForceUnwrap" : false,
+    "NeverUseForceTry" : false,
+    "NeverUseImplicitlyUnwrappedOptionals" : false,
+    "NoAccessLevelOnExtensionDeclaration" : true,
+    "NoAssignmentInExpressions" : true,
+    "NoBlockComments" : true,
+    "NoCasesWithOnlyFallthrough" : true,
+    "NoEmptyTrailingClosureParentheses" : true,
+    "NoLabelsInCasePatterns" : true,
+    "NoLeadingUnderscores" : false,
+    "NoParensAroundConditions" : true,
+    "NoPlaygroundLiterals" : true,
+    "NoVoidReturnOnFunctionSignature" : true,
+    "OmitExplicitReturns" : false,
+    "OneCasePerLine" : true,
+    "OneVariableDeclarationPerLine" : true,
+    "OnlyOneTrailingClosureArgument" : true,
+    "OrderedImports" : true,
+    "ReplaceForEachWithForLoop" : true,
+    "ReturnVoidInsteadOfEmptyTuple" : true,
+    "TypeNamesShouldBeCapitalized" : true,
+    "UseEarlyExits" : false,
+    "UseExplicitNilCheckInConditions" : true,
+    "UseLetInEveryBoundCaseVariable" : true,
+    "UseShorthandTypeNames" : true,
+    "UseSingleLinePropertyGetter" : true,
+    "UseSynthesizedInitializer" : true,
+    "UseTripleSlashForDocumentationComments" : true,
+    "UseWhereClausesInForLoops" : false,
+    "ValidateDocumentationComments" : false
+  },
+  "spacesAroundRangeFormationOperators" : true,
+  "spacesBeforeEndOfLineComments" : 1,
+  "tabWidth" : 8,
+  "version" : 1
+}

Package.swift

@@ -0,0 +1,20 @@
+// swift-tools-version: 6.1
+
+import PackageDescription
+
+let package = Package(
+    name: "dispatch-async",
+    products: [
+        .library(
+            name: "DispatchAsync",
+            targets: ["DispatchAsync"])
+    ],
+    targets: [
+        .target(
+            name: "DispatchAsync"),
+        .testTarget(
+            name: "DispatchAsyncTests",
+            dependencies: ["DispatchAsync"]
+        ),
+    ]
+)

README.md

@@ -1 +1,40 @@
-# dispatch-async
+# dispatch-async
+
+## ⚠️ WARNING - This is an 🧪experimental🧪 repository and should not be adopted at large.
+
+DispatchAsync is a temporary experimental repository aimed at implementing missing Dispatch support in the SwiftWasm toolchain.
+Currently, [SwiftWasm doesn't include Dispatch](https://book.swiftwasm.org/getting-started/porting.html#swift-foundation-and-dispatch). 
+But, SwiftWasm does support Swift Concurrency. DispatchAsync implements a number of common Dispatch API's using Swift Concurrency
+under the hood.
+
+Dispatch Async does not provide blocking API's such as `DispatchQueue.sync`, primarily due to the intentional lack of blocking
+API's in Swift Concurrency.
+
+# Toolchain Adoption Plans
+
+DispatchAsync is not meant for consumption abroad directly as a new Swift Module. Rather, the intention is to provide eventual integration
+as a drop-in replacement for Dispatch when compiling to Wasm.
+
+There are a few paths to adoption into the Swift toolchain
+
+- DispatchAsync can be emplaced inside the [libDispatch repository](https://github.com/swiftlang/swift-corelibs-libdispatch), and compiled
+into the toolchain only for wasm targets.
+- DispatchAsync can be consumed in place of libDispatch when building the Swift toolchain.
+
+Ideally, with either approach, this repository would transfer ownership to the swiftlang organization.
+
+# DispatchSemaphore Limitations
+
+The current implementation of `DispatchSemaphore` has some limitations. Blocking threads goes against the design goals of Swift Concurrency.
+The `wait` function on `DispatchSemaphore` goes against this goal. Furthermore, most wasm targets run on a single thread from the web
+browser, so any time the `wait` function ends up blocking the calling thread, it would almost certainly freeze the single-threaded wasm
+executable.
+
+To navigate these issues, there are some limitations:
+
+- For wasm compilation targets, `DispatchSemaphore` assumes single-threaded execution, and lacks various safeguards that would otherwise
+be needed for multi-threaded execution. This makes the implementation much easier.
+- For wasm targets, calls to `signal` and `wait` must be balanced. An assertion triggers if `wait` is called more times than `signal`.
+- DispatchSemaphore is deprecated for wasm targets, and AsyncSemaphore is encouraged as the replacement.
+- For non-wasm targets, DispatchSemaphore is simply a typealias for `AsyncSemaphore`, and provides only a non-blocking async `wait` 
+function. This reduces potential issues that can arise from wait being a thread-blocking function. 

Sources/DispatchAsync/AsyncSemaphore.swift

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+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2025 Apple Inc. and the Swift.org project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+// See CONTRIBUTORS.txt for the list of Swift.org project authors
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+/// Provides a semaphore implantation in `async` context, with a safe wait method. Provides easy safer replacement
+/// for DispatchSemaphore usage.
+@available(macOS 10.15, *)
+actor AsyncSemaphore {
+    private var value: Int
+    private var waiters: [CheckedContinuation<Void, Never>] = []
+
+    init(value: Int = 1) {
+        self.value = value
+    }
+
+    func wait() async {
+        value -= 1
+        if value >= 0 { return }
+        await withCheckedContinuation {
+            waiters.append($0)
+        }
+    }
+
+    func signal() {
+        self.value += 1
+
+        guard !waiters.isEmpty else { return }
+        let first = waiters.removeFirst()
+        first.resume()
+    }
+}
+
+@available(macOS 10.15, *)
+extension AsyncSemaphore {
+    func withLock<T: Sendable>(_ closure: () async throws -> T) async rethrows -> T {
+        await wait()
+        defer { signal() }
+        return try await closure()
+    }
+
+    func withLockVoid(_ closure: () async throws -> Void) async rethrows {
+        await wait()
+        defer { signal() }
+        try await closure()
+    }
+}