[OF-1524] Cross-thread Callbacks

Library/src/EmscriptenBindings/CallbackQueue.h

@@ -0,0 +1,53 @@
+/*
+    Callback queue designed to push callbacks onto the main thread using the emscripten api.
+    This works because emscriptens threads are just web workers, which allows us to push messages to different workers.
+
+    This is implemented to work around the limitation of callbacks needing to fire on the same thread they were created on.
+*/
+
+#ifdef CSP_WASM
+
+#include <emscripten.h>
+#include <emscripten/proxying.h>
+#include <emscripten/threading.h>
+#include <pthread.h>
+#include <tuple>
+
+namespace csp
+{
+static em_proxying_queue* ProxyQueue = em_proxying_queue_create();
+static pthread_t MainThread = emscripten_main_runtime_thread_id();
+
+// Structure to hold the callback and arguments.
+// With the current implementation, the first argument will always be the callback context.
+template <typename... T> struct CallbackData
+{
+    void (*Callback)(T...);
+    std::tuple<T...> Args;
+};
+
+// This function is called internally from emscripten_proxy_sync on the main thread.
+template <typename... T> static void Emscripten_CallbackWrapper(void* InData)
+{
+    auto* Data = static_cast<CallbackData<T...>*>(InData);
+    std::apply(Data->Callback, Data->Args);
+}
+
+// Function that will push the callback to the main thread if we are not on it.
+template <typename... T> static void Emscripten_CallbackOnThread(void (*Callback)(T...), T... Args)
+{
+    bool OnMainThread = pthread_equal(pthread_self(), emscripten_main_runtime_thread_id());
+    if (OnMainThread)
+    {
+        // We're on the main thread already, just call normally
+        Callback(Args...);
+    }
+    else
+    {
+        // Pack our data and send to the emscripten queue.
+        CallbackData<T...> Data { Callback, std::make_tuple(Args...) };
+        emscripten_proxy_sync(ProxyQueue, MainThread, Emscripten_CallbackWrapper<T...>, static_cast<void*>(&Data));
+    }
+}
+}
+#endif

Library/src/Multiplayer/MultiplayerConnection.cpp

@@ -203,6 +203,7 @@ namespace
         Connection->SetDisconnected(
             [&NetworkInterruptionCallback, &LogSystem](const std::exception_ptr& Except)
             {
+                // We currently detect a connection interrupt if the disconnected callback contains an exception.
                 if (Except)
                 {
                     try
@@ -212,10 +213,9 @@ namespace
                     catch (const std::exception& e)
                     {
                         INVOKE_IF_NOT_NULL(NetworkInterruptionCallback, e.what());
+                        LogSystem.LogMsg(csp::common::LogLevel::Log, "Connection Interrupted.");
                     }
                 }
-
-                LogSystem.LogMsg(csp::common::LogLevel::Log, "Connection Interrupted.");
             });
     }
 }

Tools/WrapperGenerator/Templates/C/GeneratedWrapper.mustache

@@ -12,6 +12,20 @@
 
 #pragma endregion Generated Includes
 
+#include "EmscriptenBindings/CallbackQueue.h"
+
+// Generic callback function which will either call the callback directly, or, 
+// if we're on wasm, push to the main thread if we're not on the main thread.
+template <typename ...T>
+static void CallCallback(void (*Callback)(T...), T... Args)
+{
+#ifdef CSP_WASM
+    csp::Emscripten_CallbackOnThread(Callback, Args...);
+#else
+    Callback(Args...);
+#endif
+}
+
 extern "C"
 {
     typedef struct {

Tools/WrapperGenerator/Templates/C/Partials/Class/Method/Method.mustache

@@ -239,12 +239,10 @@
             {{/ type.is_string }}
           {{/ parameters }}
 
-          {{ name }}(
-            {{ name }}_StateObject,
-
-            {{# parameters }}
+          CallCallback({{ name }}, {{ name }}_StateObject,
+              {{# parameters }}
               {{# type.is_string }}
-                _{{ name }}
+                (const char*)_{{ name }}
               {{/ type.is_string }}
 
               {{^ type.is_string }}

WasmTesting/csp-wasm.test.ts

@@ -50,9 +50,7 @@ test('Cross Thread Callbacks From Log Callback, OB-3782', async () => {
   console.log(errors);
 
   assert.ok(
-    errors.some(e => e.message.includes('table index is out of bounds')),
-    'Expected cross-thread `table index is out of bounds` error. Message not found, did you fix the bug (OB-3782)? Nice job! ',
-  );
+    !errors.some(e => e.message.includes('table index is out of bounds')));
 
 });