Add THREADS_ENABLED macro in order to compile Godot to run on the main thread

.github/workflows/web_builds.yml

@@ -17,7 +17,24 @@ concurrency:
 jobs:
   web-template:
     runs-on: "ubuntu-22.04"
-    name: Template (target=template_release)
+    name: ${{ matrix.name }}
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - name: Template w/ threads (target=template_release, threads=yes)
+            cache-name: web-template
+            target: template_release
+            sconsflags: threads=yes
+            tests: false
+            artifact: true
+
+          - name: Template w/o threads (target=template_release, threads=no)
+            cache-name: web-nothreads-template
+            target: template_release
+            sconsflags: threads=no
+            tests: false
+            artifact: true
 
     steps:
       - uses: actions/checkout@v4
@@ -34,6 +51,8 @@ jobs:
 
       - name: Setup Godot build cache
         uses: ./.github/actions/godot-cache
+        with:
+          cache-name: ${{ matrix.cache-name }}
         continue-on-error: true
 
       - name: Setup python and scons
@@ -42,10 +61,13 @@ jobs:
       - name: Compilation
         uses: ./.github/actions/godot-build
         with:
-          sconsflags: ${{ env.SCONSFLAGS }}
+          sconsflags: ${{ env.SCONSFLAGS }} ${{ matrix.sconsflags }}
           platform: web
-          target: template_release
-          tests: false
+          target: ${{ matrix.target }}
+          tests: ${{ matrix.tests }}
 
       - name: Upload artifact
         uses: ./.github/actions/upload-artifact
+        if: ${{ matrix.artifact }}
+        with:
+          name: ${{ matrix.cache-name }}

SConstruct

@@ -183,6 +183,7 @@ opts.Add(BoolVariable("separate_debug_symbols", "Extract debugging symbols to a
 opts.Add(EnumVariable("lto", "Link-time optimization (production builds)", "none", ("none", "auto", "thin", "full")))
 opts.Add(BoolVariable("production", "Set defaults to build Godot for use in production", False))
 opts.Add(BoolVariable("generate_apk", "Generate an APK/AAB after building Android library by calling Gradle", False))
+opts.Add(BoolVariable("threads", "Enable threading support", True))
 
 # Components
 opts.Add(BoolVariable("deprecated", "Enable compatibility code for deprecated and removed features", True))
@@ -832,6 +833,10 @@ if selected_platform in platform_list:
         suffix += ".double"
 
     suffix += "." + env["arch"]
+
+    if not env["threads"]:
+        suffix += ".nothreads"
+
     suffix += env.extra_suffix
 
     sys.path.remove(tmppath)
@@ -972,6 +977,9 @@ if selected_platform in platform_list:
         env.Tool("compilation_db")
         env.Alias("compiledb", env.CompilationDatabase())
 
+    if env["threads"]:
+        env.Append(CPPDEFINES=["THREADS_ENABLED"])
+
     Export("env")
 
     # Build subdirs, the build order is dependent on link order.

core/object/worker_thread_pool.cpp

@@ -47,6 +47,7 @@ WorkerThreadPool *WorkerThreadPool::singleton = nullptr;
 thread_local CommandQueueMT *WorkerThreadPool::flushing_cmd_queue = nullptr;
 
 void WorkerThreadPool::_process_task(Task *p_task) {
+#ifdef THREADS_ENABLED
 	int pool_thread_index = thread_ids[Thread::get_caller_id()];
 	ThreadData &curr_thread = threads[pool_thread_index];
 	Task *prev_task = nullptr; // In case this is recursively called.
@@ -69,6 +70,7 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 		curr_thread.current_task = p_task;
 		task_mutex.unlock();
 	}
+#endif
 
 	if (p_task->group) {
 		// Handling a group
@@ -143,6 +145,7 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 		}
 	}
 
+#ifdef THREADS_ENABLED
 	{
 		curr_thread.current_task = prev_task;
 		if (p_task->low_priority) {
@@ -159,6 +162,7 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 	}
 
 	set_current_thread_safe_for_nodes(safe_for_nodes_backup);
+#endif
 }
 
 void WorkerThreadPool::_thread_function(void *p_user) {
@@ -542,6 +546,7 @@ bool WorkerThreadPool::is_group_task_completed(GroupID p_group) const {
 }
 
 void WorkerThreadPool::wait_for_group_task_completion(GroupID p_group) {
+#ifdef THREADS_ENABLED
 	task_mutex.lock();
 	Group **groupp = groups.getptr(p_group);
 	task_mutex.unlock();
@@ -574,6 +579,7 @@ void WorkerThreadPool::wait_for_group_task_completion(GroupID p_group) {
 	task_mutex.lock(); // This mutex is needed when Physics 2D and/or 3D is selected to run on a separate thread.
 	groups.erase(p_group);
 	task_mutex.unlock();
+#endif
 }
 
 int WorkerThreadPool::get_thread_index() {

core/os/condition_variable.h

@@ -33,6 +33,8 @@
 
 #include "core/os/mutex.h"
 
+#ifdef THREADS_ENABLED
+
 #ifdef MINGW_ENABLED
 #define MINGW_STDTHREAD_REDUNDANCY_WARNING
 #include "thirdparty/mingw-std-threads/mingw.condition_variable.h"
@@ -66,4 +68,16 @@ class ConditionVariable {
 	}
 };
 
+#else // No threads.
+
+class ConditionVariable {
+public:
+	template <class BinaryMutexT>
+	void wait(const MutexLock<BinaryMutexT> &p_lock) const {}
+	void notify_one() const {}
+	void notify_all() const {}
+};
+
+#endif // THREADS_ENABLED
+
 #endif // CONDITION_VARIABLE_H

core/os/mutex.cpp

@@ -40,7 +40,11 @@ void _global_unlock() {
 	_global_mutex.unlock();
 }
 
+#ifdef THREADS_ENABLED
+
 template class MutexImpl<THREADING_NAMESPACE::recursive_mutex>;
 template class MutexImpl<THREADING_NAMESPACE::mutex>;
 template class MutexLock<MutexImpl<THREADING_NAMESPACE::recursive_mutex>>;
 template class MutexLock<MutexImpl<THREADING_NAMESPACE::mutex>>;
+
+#endif

core/os/mutex.h

@@ -43,6 +43,8 @@
 #define THREADING_NAMESPACE std
 #endif
 
+#ifdef THREADS_ENABLED
+
 template <class MutexT>
 class MutexLock;
 
@@ -125,8 +127,8 @@ class MutexLock {
 	THREADING_NAMESPACE::unique_lock<typename MutexT::StdMutexType> lock;
 
 public:
-	_ALWAYS_INLINE_ explicit MutexLock(const MutexT &p_mutex) :
-			lock(p_mutex.mutex){};
+	explicit MutexLock(const MutexT &p_mutex) :
+			lock(p_mutex.mutex) {}
 };
 
 // This specialization is needed so manual locking and MutexLock can be used
@@ -155,4 +157,38 @@ extern template class MutexImpl<THREADING_NAMESPACE::mutex>;
 extern template class MutexLock<MutexImpl<THREADING_NAMESPACE::recursive_mutex>>;
 extern template class MutexLock<MutexImpl<THREADING_NAMESPACE::mutex>>;
 
+#else // No threads.
+
+class MutexImpl {
+	mutable THREADING_NAMESPACE::mutex mutex;
+
+public:
+	void lock() const {}
+	void unlock() const {}
+	bool try_lock() const { return true; }
+};
+
+template <int Tag>
+class SafeBinaryMutex : public MutexImpl {
+	static thread_local uint32_t count;
+};
+
+template <class MutexT>
+class MutexLock {
+public:
+	MutexLock(const MutexT &p_mutex) {}
+};
+
+template <int Tag>
+class MutexLock<SafeBinaryMutex<Tag>> {
+public:
+	MutexLock(const SafeBinaryMutex<Tag> &p_mutex) {}
+	~MutexLock() {}
+};
+
+using Mutex = MutexImpl;
+using BinaryMutex = MutexImpl;
+
+#endif // THREADS_ENABLED
+
 #endif // MUTEX_H

core/os/os.cpp

@@ -504,6 +504,12 @@ bool OS::has_feature(const String &p_feature) {
 	}
 #endif
 
+#ifdef THREADS_ENABLED
+	if (p_feature == "threads") {
+		return true;
+	}
+#endif
+
 	if (_check_internal_feature_support(p_feature)) {
 		return true;
 	}

core/os/semaphore.h

@@ -31,6 +31,10 @@
 #ifndef SEMAPHORE_H
 #define SEMAPHORE_H
 
+#include <cstdint>
+
+#ifdef THREADS_ENABLED
+
 #include "core/error/error_list.h"
 #include "core/typedefs.h"
 #ifdef DEBUG_ENABLED
@@ -132,4 +136,17 @@ class Semaphore {
 #endif
 };
 
+#else // No threads.
+
+class Semaphore {
+public:
+	void post(uint32_t p_count = 1) const {}
+	void wait() const {}
+	bool try_wait() const {
+		return true;
+	}
+};
+
+#endif // THREADS_ENABLED
+
 #endif // SEMAPHORE_H

core/os/thread.cpp

@@ -33,19 +33,22 @@
 
 #include "thread.h"
 
+#ifdef THREADS_ENABLED
 #include "core/object/script_language.h"
 #include "core/templates/safe_refcount.h"
 
-Thread::PlatformFunctions Thread::platform_functions;
-
 SafeNumeric<uint64_t> Thread::id_counter(1); // The first value after .increment() is 2, hence by default the main thread ID should be 1.
 
 thread_local Thread::ID Thread::caller_id = Thread::UNASSIGNED_ID;
+#endif
+
+Thread::PlatformFunctions Thread::platform_functions;
 
 void Thread::_set_platform_functions(const PlatformFunctions &p_functions) {
 	platform_functions = p_functions;
 }
 
+#ifdef THREADS_ENABLED
 void Thread::callback(ID p_caller_id, const Settings &p_settings, Callback p_callback, void *p_userdata) {
 	Thread::caller_id = p_caller_id;
 	if (platform_functions.set_priority) {
@@ -107,4 +110,6 @@ Thread::~Thread() {
 	}
 }
 
+#endif // THREADS_ENABLED
+
 #endif // PLATFORM_THREAD_OVERRIDE

core/os/thread.h

@@ -53,6 +53,8 @@
 
 class String;
 
+#ifdef THREADS_ENABLED
+
 class Thread {
 public:
 	typedef void (*Callback)(void *p_userdata);
@@ -86,15 +88,15 @@ class Thread {
 private:
 	friend class Main;
 
+	static PlatformFunctions platform_functions;
+
 	ID id = UNASSIGNED_ID;
 	static SafeNumeric<uint64_t> id_counter;
 	static thread_local ID caller_id;
 	THREADING_NAMESPACE::thread thread;
 
 	static void callback(ID p_caller_id, const Settings &p_settings, Thread::Callback p_callback, void *p_userdata);
 
-	static PlatformFunctions platform_functions;
-
 	static void make_main_thread() { caller_id = MAIN_ID; }
 	static void release_main_thread() { caller_id = UNASSIGNED_ID; }
 
@@ -125,6 +127,64 @@ class Thread {
 	~Thread();
 };
 
+#else // No threads.
+
+class Thread {
+public:
+	typedef void (*Callback)(void *p_userdata);
+
+	typedef uint64_t ID;
+
+	enum : ID {
+		UNASSIGNED_ID = 0,
+		MAIN_ID = 1
+	};
+
+	enum Priority {
+		PRIORITY_LOW,
+		PRIORITY_NORMAL,
+		PRIORITY_HIGH
+	};
+
+	struct Settings {
+		Priority priority;
+		Settings() { priority = PRIORITY_NORMAL; }
+	};
+
+	struct PlatformFunctions {
+		Error (*set_name)(const String &) = nullptr;
+		void (*set_priority)(Thread::Priority) = nullptr;
+		void (*init)() = nullptr;
+		void (*wrapper)(Thread::Callback, void *) = nullptr;
+		void (*term)() = nullptr;
+	};
+
+private:
+	friend class Main;
+
+	static PlatformFunctions platform_functions;
+
+	static void make_main_thread() {}
+	static void release_main_thread() {}
+
+public:
+	static void _set_platform_functions(const PlatformFunctions &p_functions);
+
+	_FORCE_INLINE_ ID get_id() const { return 0; }
+	_FORCE_INLINE_ static ID get_caller_id() { return MAIN_ID; }
+	_FORCE_INLINE_ static ID get_main_id() { return MAIN_ID; }
+
+	_FORCE_INLINE_ static bool is_main_thread() { return true; }
+
+	static Error set_name(const String &p_name) { return ERR_UNAVAILABLE; }
+
+	void start(Thread::Callback p_callback, void *p_user, const Settings &p_settings = Settings()) {}
+	bool is_started() const { return false; }
+	void wait_to_finish() {}
+};
+
+#endif // THREADS_ENABLED
+
 #endif // THREAD_H
 
 #endif // PLATFORM_THREAD_OVERRIDE