Stop blocking the main thread when starting Web Worker threads

Seems like blocking the main thread also blocks the Web Worker threads
from starting on some browsers.

Author: kateinoigakukun

Sources/JavaScriptEventLoop/WebWorkerTaskExecutor.swift

@@ -263,7 +263,7 @@ public final class WebWorkerTaskExecutor: TaskExecutor {
             self.workers = workers
         }
 
-        func start() {
+        func start(timeout: Duration, checkInterval: Duration) async throws {
             class Context: @unchecked Sendable {
                 let executor: WebWorkerTaskExecutor.Executor
                 let worker: Worker
@@ -293,10 +293,16 @@ public final class WebWorkerTaskExecutor: TaskExecutor {
             }
             // Wait until all worker threads are started and wire up messaging channels
             // between the main thread and workers to notify job enqueuing events each other.
+            let clock = ContinuousClock()
+            let workerInitStarted = clock.now
             for worker in workers {
                 var tid: pid_t
                 repeat {
+                    if workerInitStarted.duration(to: .now) > timeout {
+                        fatalError("Worker thread initialization timeout exceeded (\(timeout))")
+                    }
                     tid = worker.tid.load(ordering: .sequentiallyConsistent)
+                    try await clock.sleep(for: checkInterval)
                 } while tid == 0
                 swjs_listen_main_job_from_worker_thread(tid)
             }
@@ -330,10 +336,13 @@ public final class WebWorkerTaskExecutor: TaskExecutor {
 
     /// Create a new Web Worker task executor.
     ///
-    /// - Parameter numberOfThreads: The number of Web Worker threads to spawn.
-    public init(numberOfThreads: Int) {
+    /// - Parameters:
+    ///   - numberOfThreads: The number of Web Worker threads to spawn.
+    ///   - timeout: The timeout to wait for all worker threads to be started.
+    ///   - checkInterval: The interval to check if all worker threads are started.
+    public init(numberOfThreads: Int, timeout: Duration = .seconds(3), checkInterval: Duration = .microseconds(5)) async throws {
         self.executor = Executor(numberOfThreads: numberOfThreads)
-        self.executor.start()
+        try await self.executor.start(timeout: timeout, checkInterval: checkInterval)
     }
 
     /// Terminate child Web Worker threads.

Tests/JavaScriptEventLoopTests/WebWorkerTaskExecutorTests.swift

@@ -12,8 +12,8 @@ final class WebWorkerTaskExecutorTests: XCTestCase {
         WebWorkerTaskExecutor.installGlobalExecutor()
     }
 
-    func testTaskRunOnMainThread() async {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 1)
+    func testTaskRunOnMainThread() async throws {
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 1)
 
         XCTAssertTrue(isMainThread())
 
@@ -29,15 +29,15 @@ final class WebWorkerTaskExecutorTests: XCTestCase {
         executor.terminate()
     }
 
-    func testWithPreferenceBlock() async {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 1)
+    func testWithPreferenceBlock() async throws {
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 1)
         await withTaskExecutorPreference(executor) {
             XCTAssertFalse(isMainThread())
         }
     }
 
     func testAwaitInsideTask() async throws {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 1)
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 1)
 
         let task = Task(executorPreference: executor) {
             await Task.yield()
@@ -51,7 +51,7 @@ final class WebWorkerTaskExecutorTests: XCTestCase {
     }
 
     func testSleepInsideTask() async throws {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 1)
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 1)
 
         let task = Task(executorPreference: executor) {
             XCTAssertFalse(isMainThread())
@@ -69,8 +69,8 @@ final class WebWorkerTaskExecutorTests: XCTestCase {
         executor.terminate()
     }
 
-    func testMainActorRun() async {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 1)
+    func testMainActorRun() async throws {
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 1)
 
         let task = Task(executorPreference: executor) {
             await MainActor.run {
@@ -87,8 +87,8 @@ final class WebWorkerTaskExecutorTests: XCTestCase {
         executor.terminate()
     }
 
-    func testTaskGroupRunOnSameThread() async {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 3)
+    func testTaskGroupRunOnSameThread() async throws {
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 3)
 
         let mainTid = swjs_get_worker_thread_id()
         await withTaskExecutorPreference(executor) {
@@ -112,8 +112,8 @@ final class WebWorkerTaskExecutorTests: XCTestCase {
         executor.terminate()
     }
 
-    func testTaskGroupRunOnDifferentThreads() async {
-        let executor = WebWorkerTaskExecutor(numberOfThreads: 2)
+    func testTaskGroupRunOnDifferentThreads() async throws {
+        let executor = try await WebWorkerTaskExecutor(numberOfThreads: 2)
 
         struct Item: Hashable {
             let type: String