[wasm] Add an internal GC lock API

src/mono/mono/metadata/sgen-stw.c

@@ -27,6 +27,10 @@
 #include "metadata/gc-internals.h"
 #include "utils/mono-threads.h"
 #include "utils/mono-threads-debug.h"
+#ifdef HOST_BROWSER
+#include <emscripten.h>
+#include <mono/utils/mono-threads-wasm.h>
+#endif
 
 #if _MSC_VER
 #pragma warning(disable:4312) // FIXME pointer cast to different size
@@ -485,4 +489,42 @@ mono_restart_world (MonoThreadInfoFlags flags)
 	release_gc_locks ();
 	UNLOCK_GC;
 }
+
+#ifdef HOST_BROWSER
+
+EMSCRIPTEN_KEEPALIVE void mono_wasm_gc_lock(void);
+EMSCRIPTEN_KEEPALIVE void mono_wasm_gc_unlock(void);
+
+/* Allow the main thread to take the GC lock from JS */
+EMSCRIPTEN_KEEPALIVE
+void
+mono_wasm_gc_lock(void)
+{
+	MONO_ENTER_GC_UNSAFE;
+#ifndef DISABLE_THREADS
+	/* only the browser thread is allowed to take the GC lock */
+	g_assert (mono_threads_wasm_is_browser_thread ());
+	LOCK_GC;
+	acquire_gc_locks();
+#else
+	g_assert_not_reached ();
+#endif
+	MONO_EXIT_GC_UNSAFE;
+}
+
+EMSCRIPTEN_KEEPALIVE
+void
+mono_wasm_gc_unlock(void)
+{
+	MONO_ENTER_GC_UNSAFE;
+#ifndef DISABLE_THREADS
+	release_gc_locks();
+	UNLOCK_GC;
+#else
+	g_assert_not_reached ();
+#endif
+	MONO_EXIT_GC_UNSAFE;
+}
+#endif /* HOST_BROWSER */
+
 #endif

src/mono/wasm/runtime/cwraps.ts

@@ -98,6 +98,8 @@ const fn_signatures: SigLine[] = [
     [true, "mono_wasm_f64_to_u52", "number", ["number", "number"]],
     [true, "mono_wasm_method_get_name", "number", ["number"]],
     [true, "mono_wasm_method_get_full_name", "number", ["number"]],
+    [true, "mono_wasm_gc_lock", "void", []],
+    [true, "mono_wasm_gc_unlock", "void", []],
 
     // jiterpreter
     [true, "mono_jiterp_get_trace_bailout_count", "number", ["number"]],
@@ -239,6 +241,8 @@ export interface t_Cwraps {
     mono_wasm_runtime_run_module_cctor(assembly: MonoAssembly): void;
     mono_wasm_method_get_name(method: MonoMethod): CharPtr;
     mono_wasm_method_get_full_name(method: MonoMethod): CharPtr;
+    mono_wasm_gc_lock(): void;
+    mono_wasm_gc_unlock(): void;
 
     mono_jiterp_get_trace_bailout_count(reason: number): number;
     mono_jiterp_value_copy(destination: VoidPtr, source: VoidPtr, klass: MonoClass): void;

src/mono/wasm/runtime/exports-internal.ts

@@ -14,6 +14,7 @@ import { ws_wasm_create, ws_wasm_open, ws_wasm_send, ws_wasm_receive, ws_wasm_cl
 import { mono_wasm_get_loaded_files } from "./assets";
 import { jiterpreter_dump_stats } from "./jiterpreter";
 import { getOptions, applyOptions } from "./jiterpreter-support";
+import { mono_wasm_gc_lock, mono_wasm_gc_unlock } from "./gc-lock";
 
 export function export_internal(): any {
     return {
@@ -80,7 +81,11 @@ export function export_internal(): any {
         // jiterpreter
         jiterpreter_dump_stats,
         jiterpreter_apply_options: applyOptions,
-        jiterpreter_get_options: getOptions
+        jiterpreter_get_options: getOptions,
+
+        // Blazor GC Lock support
+        mono_wasm_gc_lock,
+        mono_wasm_gc_unlock,
     };
 }
 

src/mono/wasm/runtime/gc-lock.ts

@@ -0,0 +1,31 @@
+import MonoWasmThreads from "consts:monoWasmThreads";
+import { ENVIRONMENT_IS_PTHREAD } from "./imports";
+import cwraps from "./cwraps";
+
+let locked = false;
+
+export function mono_wasm_gc_lock(): void {
+    if (locked) {
+        throw new Error("GC is already locked");
+    }
+    if (MonoWasmThreads) {
+        if (ENVIRONMENT_IS_PTHREAD) {
+            throw new Error("GC lock only supported in main thread");
+        }
+        cwraps.mono_wasm_gc_lock();
+    }
+    locked = true;
+}
+
+export function mono_wasm_gc_unlock(): void {
+    if (!locked) {
+        throw new Error("GC is not locked");
+    }
+    if (MonoWasmThreads) {
+        if (ENVIRONMENT_IS_PTHREAD) {
+            throw new Error("GC lock only supported in main thread");
+        }
+        cwraps.mono_wasm_gc_unlock();
+    }
+    locked = false;
+}