[wasm][mt] Guard more places for blocking wait on JS interop threads

src/libraries/System.Private.CoreLib/src/System/Threading/LowLevelMonitor.Unix.cs

@@ -31,6 +31,9 @@ private void DisposeCore()
 
         private void AcquireCore()
         {
+#if FEATURE_WASM_MANAGED_THREADS
+            Thread.AssureBlockingPossible();
+#endif
             Interop.Sys.LowLevelMonitor_Acquire(_nativeMonitor);
         }
 
@@ -41,6 +44,9 @@ private void ReleaseCore()
 
         private void WaitCore()
         {
+#if FEATURE_WASM_MANAGED_THREADS
+            Thread.AssureBlockingPossible();
+#endif
             Interop.Sys.LowLevelMonitor_Wait(_nativeMonitor);
         }
 
@@ -54,6 +60,10 @@ private bool WaitCore(int timeoutMilliseconds)
                 return true;
             }
 
+#if FEATURE_WASM_MANAGED_THREADS
+            Thread.AssureBlockingPossible();
+#endif
+
             return Interop.Sys.LowLevelMonitor_TimedWait(_nativeMonitor, timeoutMilliseconds);
         }
 

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/WebWorkerTest.cs

@@ -439,7 +439,8 @@ await executor.Execute(async () =>
         [Theory, MemberData(nameof(GetTargetThreadsAndBlockingCalls))]
         public async Task WaitAssertsOnJSInteropThreads(Executor executor, NamedCall method)
         {
-            using var cts = CreateTestCaseTimeoutSource();
+            CancellationTokenSource? cts = null;
+            Thread.ForceBlockingWait((_) => cts = CreateTestCaseTimeoutSource(), null);
             await executor.Execute(Task () =>
             {
                 Exception? exception = null;

src/libraries/System.Runtime.InteropServices.JavaScript/tests/System.Runtime.InteropServices.JavaScript.UnitTests/System/Runtime/InteropServices/JavaScript/WebWorkerTestBase.cs

@@ -165,6 +165,22 @@ public class NamedCall
                         sem.Wait(cts.Token);
                     } catch (OperationCanceledException) { /* ignore */ }
                 }},
+                new NamedCall { Name = "CancellationTokenSource.ctor", Call = delegate (CancellationToken ct) {
+                    using var cts = new CancellationTokenSource(8);
+                }},
+                new NamedCall { Name = "Mutex.WaitOne", Call = delegate (CancellationToken ct) {
+                    using var mr = new ManualResetEventSlim(false);
+                    var mutex = new Mutex();
+                    var thread = new Thread(() => {
+                        mutex.WaitOne();
+                        mr.Set();
+                        Thread.Sleep(50);
+                        mutex.ReleaseMutex();
+                    });
+                    thread.Start();
+                    Thread.ForceBlockingWait((_) => mr.Wait(), null);
+                    mutex.WaitOne();
+                }},
         };
 
         public static IEnumerable<object[]> GetTargetThreadsAndBlockingCalls()