[browser][mt] drop managed keepalive from thread pool (#99524)

src/mono/System.Private.CoreLib/src/System/Threading/PortableThreadPool.Browser.Threads.Mono.cs

@@ -7,7 +7,7 @@ internal sealed partial class PortableThreadPool
 {
     private static partial class WorkerThread
     {
-        private static bool IsIOPending => WebWorkerEventLoop.HasJavaScriptInteropDependents;
+        private static bool IsIOPending => false;
     }
 
     private struct CpuUtilizationReader

src/mono/System.Private.CoreLib/src/System/Threading/PortableThreadPool.WorkerThread.Browser.Threads.Mono.cs

@@ -37,7 +37,7 @@ private static partial class WorkerThread
 
             private static readonly ThreadStart s_workerThreadStart = WorkerThreadStart;
 
-            private sealed record SemaphoreWaitState(PortableThreadPool ThreadPoolInstance, LowLevelLock ThreadAdjustmentLock, WebWorkerEventLoop.KeepaliveToken KeepaliveToken)
+            private sealed record SemaphoreWaitState(PortableThreadPool ThreadPoolInstance, LowLevelLock ThreadAdjustmentLock)
             {
                 public bool SpinWait = true;
 
@@ -59,8 +59,7 @@ private static void WorkerThreadStart()
                 }
 
                 LowLevelLock threadAdjustmentLock = threadPoolInstance._threadAdjustmentLock;
-                var keepaliveToken = WebWorkerEventLoop.KeepalivePush();
-                SemaphoreWaitState state = new(threadPoolInstance, threadAdjustmentLock, keepaliveToken) { SpinWait = true };
+                SemaphoreWaitState state = new(threadPoolInstance, threadAdjustmentLock) { SpinWait = true };
                 // set up the callbacks for semaphore waits, tell
                 // emscripten to keep the thread alive, and return to
                 // the JS event loop.
@@ -74,8 +73,6 @@ private static void WorkerThreadStart()
             private static void WaitForWorkLoop(LowLevelLifoAsyncWaitSemaphore semaphore, SemaphoreWaitState state)
             {
                 semaphore.PrepareAsyncWait(ThreadPoolThreadTimeoutMs, s_WorkLoopSemaphoreSuccess, s_WorkLoopSemaphoreTimedOut, state);
-                // thread should still be kept alive
-                Debug.Assert(state.KeepaliveToken.Valid);
             }
 
             private static void WorkLoopSemaphoreSuccess(LowLevelLifoAsyncWaitSemaphore semaphore, object? stateObject)
@@ -91,11 +88,6 @@ private static void WorkLoopSemaphoreTimedOut(LowLevelLifoAsyncWaitSemaphore sem
                 SemaphoreWaitState state = (SemaphoreWaitState)stateObject!;
                 if (ShouldExitWorker(state.ThreadPoolInstance, state.ThreadAdjustmentLock)) {
                     // we're done, kill the thread.
-
-                    // we're wrapped in an emscripten eventloop handler which will consult the
-                    // keepalive count, destroy the thread and run the TLS dtor which will
-                    // unregister the thread from Mono
-                    state.KeepaliveToken.Pop();
                     return;
                 } else {
                     // more work showed up while we were shutting down, go around one more time

src/mono/System.Private.CoreLib/src/System/Threading/WebWorkerEventLoop.Browser.Threads.Mono.cs

@@ -12,49 +12,6 @@ namespace System.Threading;
 /// </summary>
 internal static class WebWorkerEventLoop
 {
-    // FIXME: these keepalive calls could be qcalls with a SuppressGCTransitionAttribute
-    [MethodImpl(MethodImplOptions.InternalCall)]
-    private static extern void KeepalivePushInternal();
-    [MethodImpl(MethodImplOptions.InternalCall)]
-    private static extern void KeepalivePopInternal();
-
-    /// <summary>
-    /// A keepalive token prevents a thread from shutting down even if it returns to the JS event
-    /// loop.  A thread may want a keepalive token if it needs to allow JS code to run to settle JS
-    /// promises or execute JS timeout callbacks.
-    /// </summary>
-    internal sealed class KeepaliveToken
-    {
-        public bool Valid {get; private set; }
-
-        private KeepaliveToken() { Valid = true; }
-
-        /// <summary>
-        ///  Decrement the Emscripten keepalive count.  A thread with a zero keepalive count will
-        ///  terminate when it returns from its start function or from an async invocation from the
-        ///  JS event loop.
-        /// </summary>
-        internal void Pop() {
-            if (!Valid)
-                throw new InvalidOperationException();
-            Valid = false;
-            KeepalivePopInternal();
-        }
-
-        internal static KeepaliveToken Create()
-        {
-            KeepalivePushInternal();
-            return new KeepaliveToken();
-        }
-    }
-
-    /// <summary>
-    ///  Increment the Emscripten keepalive count.  A thread with a positive keepalive can return from its
-    ///  thread start function or a JS event loop invocation and continue running in the JS event
-    ///  loop.
-    /// </summary>
-    internal static KeepaliveToken KeepalivePush() => KeepaliveToken.Create();
-
     /// <summary>
     ///   Start a thread that may be kept alive on its webworker after the start function returns,
     ///   if the emscripten keepalive count is positive.  Once the thread returns to the JS event
@@ -73,26 +30,4 @@ internal static void StartExitable(Thread thread, bool captureContext)
         thread.HasExternalEventLoop = true;
         thread.UnsafeStart();
     }
-
-    /// returns true if the current thread has unsettled JS Interop promises
-    private static bool HasUnsettledInteropPromises => HasUnsettledInteropPromisesNative();
-
-    // FIXME: this could be a qcall with a SuppressGCTransitionAttribute
-    [MethodImpl(MethodImplOptions.InternalCall)]
-    private static extern bool HasUnsettledInteropPromisesNative();
-
-    /// <summary>returns true if the current WebWorker has JavaScript objects that depend on the
-    /// current managed thread.</summary>
-    ///
-    /// <remarks>If this returns false, the runtime is allowed to allow the current managed thread
-    /// to exit and for the WebWorker to be recycled by Emscripten for another managed
-    /// thread.</remarks>
-    internal static bool HasJavaScriptInteropDependents
-    {
-        //
-        // FIXME:
-        // https://github.com/dotnet/runtime/issues/85052 - unsettled promises are not the only relevant
-        // reasons for keeping a worker thread alive. We will need to add other conditions here.
-        get => HasUnsettledInteropPromises;
-    }
 }

src/mono/browser/runtime/cancelable-promise.ts

@@ -9,7 +9,6 @@ import { ControllablePromise, GCHandle, MarshalerToCs } from "./types/internal";
 import { ManagedObject } from "./marshal";
 import { compareExchangeI32, forceThreadMemoryViewRefresh } from "./memory";
 import { mono_log_debug } from "./logging";
-import { settleUnsettledPromise } from "./pthreads";
 import { complete_task } from "./managed-exports";
 import { marshal_cs_object_to_cs } from "./marshal-to-cs";
 
@@ -163,7 +162,6 @@ export class PromiseHolder extends ManagedObject {
             this.isPosted = true;
             if (WasmEnableThreads) {
                 forceThreadMemoryViewRefresh();
-                settleUnsettledPromise();
             }
 
             // we can unregister the GC handle just on JS side

src/mono/browser/runtime/exports-binding.ts

@@ -27,7 +27,7 @@ import { mono_wasm_browser_entropy } from "./crypto";
 import { mono_wasm_cancel_promise } from "./cancelable-promise";
 
 import {
-    mono_wasm_eventloop_has_unsettled_interop_promises, mono_wasm_start_deputy_thread_async,
+    mono_wasm_start_deputy_thread_async,
     mono_wasm_pthread_on_pthread_attached, mono_wasm_pthread_on_pthread_unregistered,
     mono_wasm_pthread_on_pthread_registered, mono_wasm_pthread_set_name, mono_wasm_install_js_worker_interop, mono_wasm_uninstall_js_worker_interop
 } from "./pthreads";
@@ -44,8 +44,6 @@ export const mono_wasm_threads_imports = !WasmEnableThreads ? [] : [
     mono_wasm_pthread_set_name,
     mono_wasm_start_deputy_thread_async,
 
-    // threads.c
-    mono_wasm_eventloop_has_unsettled_interop_promises,
     // mono-threads.c
     mono_wasm_dump_threads,
     // diagnostics_server.c

src/mono/browser/runtime/marshal-to-cs.ts

@@ -22,7 +22,6 @@ import { _zero_region, localHeapViewF64, localHeapViewI32, localHeapViewU8 } fro
 import { stringToMonoStringRoot, stringToUTF16 } from "./strings";
 import { JSMarshalerArgument, JSMarshalerArguments, JSMarshalerType, MarshalerToCs, MarshalerToJs, BoundMarshalerToCs, MarshalerType } from "./types/internal";
 import { TypedArray } from "./types/emscripten";
-import { addUnsettledPromise } from "./pthreads";
 import { gc_locked } from "./gc-lock";
 
 export const jsinteropDoc = "For more information see https://aka.ms/dotnet-wasm-jsinterop";
@@ -339,9 +338,6 @@ function _marshal_task_to_cs(arg: JSMarshalerArgument, value: Promise<any>, _?:
         (holder as any)[proxy_debug_symbol] = `PromiseHolder with GCHandle ${gc_handle}`;
     }
 
-    if (WasmEnableThreads)
-        addUnsettledPromise();
-
     value.then(data => holder.resolve(data), reason => holder.reject(reason));
 }
 

src/mono/browser/runtime/pthreads/index.ts

@@ -10,7 +10,6 @@ export {
     populateEmscriptenPool, mono_wasm_init_threads, init_finalizer_thread,
     waitForThread, replaceEmscriptenPThreadUI
 } from "./ui-thread";
-export { addUnsettledPromise, settleUnsettledPromise, mono_wasm_eventloop_has_unsettled_interop_promises } from "./worker-eventloop";
 export {
     mono_wasm_pthread_on_pthread_attached, mono_wasm_pthread_on_pthread_unregistered,
     mono_wasm_pthread_on_pthread_registered, mono_wasm_pthread_set_name, currentWorkerThreadEvents,

src/mono/mono/metadata/icall-decl.h

@@ -194,9 +194,6 @@ ICALL_EXPORT void     ves_icall_System_Threading_LowLevelLifoSemaphore_ReleaseIn
 ICALL_EXPORT gpointer ves_icall_System_Threading_LowLevelLifoAsyncWaitSemaphore_InitInternal (void);
 ICALL_EXPORT void   ves_icall_System_Threading_LowLevelLifoAsyncWaitSemaphore_PrepareAsyncWaitInternal (gpointer sem_ptr, gint32 timeout_ms, gpointer success_cb, gpointer timeout_cb, intptr_t user_data);
 
-ICALL_EXPORT MonoBoolean ves_icall_System_Threading_WebWorkerEventLoop_HasUnsettledInteropPromisesNative(void);
-ICALL_EXPORT void ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePushInternal (void);
-ICALL_EXPORT void ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePopInternal (void);
 #endif
 
 #ifdef TARGET_AMD64

src/mono/mono/metadata/icall-def.h

@@ -615,14 +615,6 @@ HANDLES(THREAD_10, "SetState", ves_icall_System_Threading_Thread_SetState, void,
 HANDLES(THREAD_13, "StartInternal", ves_icall_System_Threading_Thread_StartInternal, void, 2, (MonoThreadObject, gint32))
 NOHANDLES(ICALL(THREAD_14, "YieldInternal", ves_icall_System_Threading_Thread_YieldInternal))
 
-/* include these icalls if we're in the threaded wasm runtime, or if we're building a wasm-targeting cross compiler and we need to support --print-icall-table */
-#if (defined(HOST_BROWSER) && !defined(DISABLE_THREADS)) || (defined(TARGET_WASM) && defined(ENABLE_ICALL_SYMBOL_MAP))
-ICALL_TYPE(WEBWORKERLOOP, "System.Threading.WebWorkerEventLoop", WEBWORKERLOOP_1)
-NOHANDLES(ICALL(WEBWORKERLOOP_1, "HasUnsettledInteropPromisesNative", ves_icall_System_Threading_WebWorkerEventLoop_HasUnsettledInteropPromisesNative))
-NOHANDLES(ICALL(WEBWORKERLOOP_2, "KeepalivePopInternal", ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePopInternal))
-NOHANDLES(ICALL(WEBWORKERLOOP_3, "KeepalivePushInternal", ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePushInternal))
-#endif
-
 ICALL_TYPE(TYPE, "System.Type", TYPE_1)
 HANDLES(TYPE_1, "internal_from_handle", ves_icall_System_Type_internal_from_handle, MonoReflectionType, 1, (MonoType_ref))
 

src/mono/mono/metadata/threads.c

@@ -4996,26 +4996,6 @@ ves_icall_System_Threading_LowLevelLifoAsyncWaitSemaphore_PrepareAsyncWaitIntern
 	mono_lifo_semaphore_asyncwait_prepare_wait (sem, timeout_ms, (LifoSemaphoreAsyncWaitCallbackFn)success_cb, (LifoSemaphoreAsyncWaitCallbackFn)timedout_cb, user_data);
 }
 
-void
-ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePushInternal (void)
-{
-	emscripten_runtime_keepalive_push();
-}
-
-void
-ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePopInternal (void)
-{
-	emscripten_runtime_keepalive_pop();
-}
-
-extern int mono_wasm_eventloop_has_unsettled_interop_promises(void);
-
-MonoBoolean
-ves_icall_System_Threading_WebWorkerEventLoop_HasUnsettledInteropPromisesNative(void)
-{
-	return !!mono_wasm_eventloop_has_unsettled_interop_promises();
-}
-
 #endif /* HOST_BROWSER && !DISABLE_THREADS */
 
 /* for the AOT cross compiler with --print-icall-table these don't need to be callable, they just
@@ -5033,22 +5013,5 @@ ves_icall_System_Threading_LowLevelLifoAsyncWaitSemaphore_PrepareAsyncWaitIntern
 	g_assert_not_reached ();
 }
 
-void
-ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePushInternal (void)
-{
-	g_assert_not_reached();
-}
-
-void
-ves_icall_System_Threading_WebWorkerEventLoop_KeepalivePopInternal (void)
-{
-	g_assert_not_reached();
-}
-
-MonoBoolean
-ves_icall_System_Threading_WebWorkerEventLoop_HasUnsettledInteropPromisesNative(void)
-{
-	g_assert_not_reached();
-}
 #endif /* defined(TARGET_WASM) && defined(ENABLE_ICALL_SYMBOL_MAP) */