Add option for experimental use of thread in Web

Might not run well in certain browsers, requires rebuilding all dependencies for Web with `pthread` enabled.
Disabled by default (for now).

Source/Engine/Platform/Web/WebPlatform.h

@@ -54,23 +54,39 @@ public:
     }
     FORCE_INLINE static int32 AtomicRead(int32 const volatile* dst)
     {
+#ifdef __EMSCRIPTEN_PTHREADS__
         int32 result;
         __atomic_load(dst, &result, __ATOMIC_SEQ_CST);
         return result;
+#else
+        return *dst;
+#endif
     }
     FORCE_INLINE static int64 AtomicRead(int64 const volatile* dst)
     {
+#ifdef __EMSCRIPTEN_PTHREADS__
         int64 result;
         __atomic_load(dst, &result, __ATOMIC_SEQ_CST);
         return result;
+#else
+        return *dst;
+#endif
     }
     FORCE_INLINE static void AtomicStore(int32 volatile* dst, int32 value)
     {
+#ifdef __EMSCRIPTEN_PTHREADS__
         __atomic_store(dst, &value, __ATOMIC_SEQ_CST);
+#else
+        *dst = value;
+#endif
     }
     FORCE_INLINE static void AtomicStore(int64 volatile* dst, int64 value)
     {
+#ifdef __EMSCRIPTEN_PTHREADS__
         __atomic_store(dst, &value, __ATOMIC_SEQ_CST);
+#else
+        *dst = value;
+#endif
     }
     FORCE_INLINE static uint64 GetCurrentThreadID()
     {

Source/Platforms/Web/Binaries/Data/NvCloth/NvCloth/compiler/cmake/web/CMakeLists.txt

@@ -37,3 +37,5 @@ FIND_PACKAGE(PxShared REQUIRED)
 
 # Include all of the projects
 INCLUDE(NvCloth.cmake)
+
+SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${NVCLOTH_CXX_FLAGS}")

Source/Tools/Flax.Build/Deps/Dependencies/NvCloth.cs

@@ -154,6 +154,8 @@ namespace Flax.Deps.Dependencies
             case TargetPlatform.Web:
                 cmakeArgs += " -DTARGET_BUILD_PLATFORM=web";
                 cmakeArgs += $" -DCMAKE_TOOLCHAIN_FILE=\"{EmscriptenSdk.Instance.CMakeToolchainPath}\"";
+                if (Configuration.WebThreads)
+                    cmakeArgs += " -DNVCLOTH_CXX_FLAGS=\"-pthread\"";
                 cmakeName = "web";
                 binariesPrefix = "lib";
 

Source/Tools/Flax.Build/Deps/Dependencies/PhysX.cs

@@ -86,6 +86,9 @@ namespace Flax.Deps.Dependencies
                 ConfigureCmakeSwitch(cmakeParams, "CMAKE_OSX_DEPLOYMENT_TARGET", Configuration.iOSMinVer);
                 ConfigureCmakeSwitch(cmakeParams, "CMAKE_XCODE_ATTRIBUTE_IPHONEOS_DEPLOYMENT_TARGET", Configuration.iOSMinVer);
                 break;
+            case TargetPlatform.Web:
+                ConfigureCmakeSwitch(cmakeParams, "PHYSX_CXX_FLAGS", Configuration.WebThreads ? "\"-pthread\"" : "");
+                break;
             }
 
             // Save preset

Source/Tools/Flax.Build/Deps/Dependencies/basis_universal.cs

@@ -112,6 +112,8 @@ namespace Flax.Deps.Dependencies
                         foreach (var define in defines)
                             cmakeArgs += $"-D{define.Key}={define.Value} ";
                     }
+                    if (platform == TargetPlatform.Web && Configuration.WebThreads)
+                        cmakeArgs += "-pthread ";
                     cmakeArgs += "\"";
 
                     var depsFolder = GetThirdPartyFolder(options, platform, architecture);

Source/Tools/Flax.Build/Platforms/Web/WebToolchain.cs

@@ -16,6 +16,12 @@ namespace Flax.Build
         /// </summary>
         [CommandLine("webInitialMemory", "<size_mb>", "Specifies the initial memory size (in MB) to use by Web app.")]
         public static int WebInitialMemory = 32;
+
+        /// <summary>
+        /// Enables pthreads support for multithreading using SharedArrayBuffer in browsers. Changing it requires rebuilding deps for Web.
+        /// </summary>
+        [CommandLine("webThreads", "0/1", "Enables pthreads support for multithreading using SharedArrayBuffer in browsers. Changing it requires rebuilding deps for Web.")]
+        public static bool WebThreads = false;
     }
 }
 
@@ -94,6 +100,8 @@ namespace Flax.Build.Platforms
             options.CompileEnv.PreprocessorDefinitions.Add("PLATFORM_WEB");
             options.CompileEnv.PreprocessorDefinitions.Add("PLATFORM_UNIX");
             options.CompileEnv.PreprocessorDefinitions.Add("__EMSCRIPTEN__");
+            if (Configuration.WebThreads)
+                options.CompileEnv.PreprocessorDefinitions.Add("__EMSCRIPTEN_PTHREADS__");
             options.CompileEnv.EnableExceptions = false;
             options.CompileEnv.CpuArchitecture = CpuArchitecture.SSE4_2;
         }
@@ -163,6 +171,9 @@ namespace Flax.Build.Platforms
                 args.Add("-fsanitize=undefined");
             if (sanitizers == Sanitizer.None)
                 args.Add("-fsanitize=null -fsanitize-minimal-runtime"); // Minimal Runtime
+
+            if (Configuration.WebThreads)
+                args.Add("-pthread");
         }
 
         /// <inheritdoc />