Modernize Thread

- Based on C++11's `thread` and `thread_local`
- No more need to allocate-deallocate or check for null
- No pointer anymore, just a member variable
- Platform-specific implementations no longer needed (except for the few cases of non-portable functions)
- Simpler for `NO_THREADS`
- Thread ids are now the same across platforms (main is 1; others follow)

9 files changed, 33 insertions, 48 deletions

diff --git a/editor/audio_stream_preview.cpp b/editor/audio_stream_preview.cpp
index 2e0c3491f7..8be8735f3e 100644
--- a/editor/audio_stream_preview.cpp
+++ b/editor/audio_stream_preview.cpp
@@ -197,7 +197,8 @@ Ref<AudioStreamPreview> AudioStreamPreviewGenerator::generate_preview(const Ref<
 	preview->preview->length = len_s;
 
 	if (preview->playback.is_valid()) {
-		preview->thread = Thread::create(_preview_thread, preview);
+		preview->thread = memnew(Thread);
+		preview->thread->start(_preview_thread, preview);
 	}
 
 	return preview->preview;
@@ -218,7 +219,8 @@ void AudioStreamPreviewGenerator::_notification(int p_what) {
 		for (Map<ObjectID, Preview>::Element *E = previews.front(); E; E = E->next()) {
 			if (!E->get().generating) {
 				if (E->get().thread) {
-					Thread::wait_to_finish(E->get().thread);
+					E->get().thread->wait_to_finish();
+					memdelete(E->get().thread);
 					E->get().thread = nullptr;
 				}
 				if (!ObjectDB::get_instance(E->key())) { //no longer in use, get rid of preview
diff --git a/editor/editor_file_system.cpp b/editor/editor_file_system.cpp
index 76814ea378..4b68de26e7 100644
--- a/editor/editor_file_system.cpp
+++ b/editor/editor_file_system.cpp
@@ -595,7 +595,7 @@ void EditorFileSystem::scan() {
 		return;
 	}
 
-	if (scanning || scanning_changes || thread) {
+	if (scanning || scanning_changes || thread.is_started()) {
 		return;
 	}
 
@@ -619,13 +619,13 @@ void EditorFileSystem::scan() {
 		_queue_update_script_classes();
 		first_scan = false;
 	} else {
-		ERR_FAIL_COND(thread);
+		ERR_FAIL_COND(thread.is_started());
 		set_process(true);
 		Thread::Settings s;
 		scanning = true;
 		scan_total = 0;
 		s.priority = Thread::PRIORITY_LOW;
-		thread = Thread::create(_thread_func, this, s);
+		thread.start(_thread_func, this, s);
 		//tree->hide();
 		//progress->show();
 	}
@@ -1046,7 +1046,7 @@ void EditorFileSystem::_thread_func_sources(void *_userdata) {
 
 void EditorFileSystem::scan_changes() {
 	if (first_scan || // Prevent a premature changes scan from inhibiting the first full scan
-			scanning || scanning_changes || thread) {
+			scanning || scanning_changes || thread.is_started()) {
 		scan_changes_pending = true;
 		set_process(true);
 		return;
@@ -1076,12 +1076,12 @@ void EditorFileSystem::scan_changes() {
 		scanning_changes_done = true;
 		emit_signal("sources_changed", sources_changed.size() > 0);
 	} else {
-		ERR_FAIL_COND(thread_sources);
+		ERR_FAIL_COND(thread_sources.is_started());
 		set_process(true);
 		scan_total = 0;
 		Thread::Settings s;
 		s.priority = Thread::PRIORITY_LOW;
-		thread_sources = Thread::create(_thread_func_sources, this, s);
+		thread_sources.start(_thread_func_sources, this, s);
 	}
 }
 
@@ -1092,17 +1092,14 @@ void EditorFileSystem::_notification(int p_what) {
 
 		} break;
 		case NOTIFICATION_EXIT_TREE: {
-			Thread *active_thread = thread ? thread : thread_sources;
-			if (use_threads && active_thread) {
+			Thread &active_thread = thread.is_started() ? thread : thread_sources;
+			if (use_threads && active_thread.is_started()) {
 				//abort thread if in progress
 				abort_scan = true;
 				while (scanning) {
 					OS::get_singleton()->delay_usec(1000);
 				}
-				Thread::wait_to_finish(active_thread);
-				memdelete(active_thread);
-				thread = nullptr;
-				thread_sources = nullptr;
+				active_thread.wait_to_finish();
 				WARN_PRINT("Scan thread aborted...");
 				set_process(false);
 			}
@@ -1125,9 +1122,7 @@ void EditorFileSystem::_notification(int p_what) {
 
 						set_process(false);
 
-						Thread::wait_to_finish(thread_sources);
-						memdelete(thread_sources);
-						thread_sources = nullptr;
+						thread_sources.wait_to_finish();
 						if (_update_scan_actions()) {
 							emit_signal("filesystem_changed");
 						}
@@ -1135,7 +1130,7 @@ void EditorFileSystem::_notification(int p_what) {
 						_queue_update_script_classes();
 						first_scan = false;
 					}
-				} else if (!scanning && thread) {
+				} else if (!scanning && thread.is_started()) {
 					set_process(false);
 
 					if (filesystem) {
@@ -1143,9 +1138,7 @@ void EditorFileSystem::_notification(int p_what) {
 					}
 					filesystem = new_filesystem;
 					new_filesystem = nullptr;
-					Thread::wait_to_finish(thread);
-					memdelete(thread);
-					thread = nullptr;
+					thread.wait_to_finish();
 					_update_scan_actions();
 					emit_signal("filesystem_changed");
 					emit_signal("sources_changed", sources_changed.size() > 0);
@@ -2080,11 +2073,9 @@ EditorFileSystem::EditorFileSystem() {
 	filesystem = memnew(EditorFileSystemDirectory); //like, empty
 	filesystem->parent = nullptr;
 
-	thread = nullptr;
 	scanning = false;
 	importing = false;
 	use_threads = true;
-	thread_sources = nullptr;
 	new_filesystem = nullptr;
 
 	abort_scan = false;
diff --git a/editor/editor_file_system.h b/editor/editor_file_system.h
index c0e11a0402..fa0b89e667 100644
--- a/editor/editor_file_system.h
+++ b/editor/editor_file_system.h
@@ -127,7 +127,7 @@ class EditorFileSystem : public Node {
 	};
 
 	bool use_threads;
-	Thread *thread;
+	Thread thread;
 	static void _thread_func(void *_userdata);
 
 	EditorFileSystemDirectory *new_filesystem;
@@ -189,7 +189,7 @@ class EditorFileSystem : public Node {
 
 	void _scan_new_dir(EditorFileSystemDirectory *p_dir, DirAccess *da, const ScanProgress &p_progress);
 
-	Thread *thread_sources;
+	Thread thread_sources;
 	bool scanning_changes;
 	bool scanning_changes_done;
 
diff --git a/editor/editor_node.cpp b/editor/editor_node.cpp
index 0ef21d3a11..62f4b21d5c 100644
--- a/editor/editor_node.cpp
+++ b/editor/editor_node.cpp
@@ -5485,9 +5485,7 @@ int EditorNode::execute_and_show_output(const String &p_title, const String &p_p
 
 	int prev_len = 0;
 
-	eta.execute_output_thread = Thread::create(_execute_thread, &eta);
-
-	ERR_FAIL_COND_V(!eta.execute_output_thread, 0);
+	eta.execute_output_thread.start(_execute_thread, &eta);
 
 	while (!eta.done) {
 		{
@@ -5502,8 +5500,7 @@ int EditorNode::execute_and_show_output(const String &p_title, const String &p_p
 		OS::get_singleton()->delay_usec(1000);
 	}
 
-	Thread::wait_to_finish(eta.execute_output_thread);
-	memdelete(eta.execute_output_thread);
+	eta.execute_output_thread.wait_to_finish();
 	execute_outputs->add_text("\nExit Code: " + itos(eta.exitcode));
 
 	if (p_close_on_errors && eta.exitcode != 0) {
diff --git a/editor/editor_node.h b/editor/editor_node.h
index 1da162dc9c..356ac0caac 100644
--- a/editor/editor_node.h
+++ b/editor/editor_node.h
@@ -108,7 +108,7 @@ public:
 		String path;
 		List<String> args;
 		String output;
-		Thread *execute_output_thread = nullptr;
+		Thread execute_output_thread;
 		Mutex execute_output_mutex;
 		int exitcode = 0;
 		volatile bool done = false;
diff --git a/editor/editor_resource_preview.cpp b/editor/editor_resource_preview.cpp
index 29a929d179..8056846f52 100644
--- a/editor/editor_resource_preview.cpp
+++ b/editor/editor_resource_preview.cpp
@@ -424,26 +424,23 @@ void EditorResourcePreview::check_for_invalidation(const String &p_path) {
 }
 
 void EditorResourcePreview::start() {
-	ERR_FAIL_COND_MSG(thread, "Thread already started.");
-	thread = Thread::create(_thread_func, this);
+	ERR_FAIL_COND_MSG(thread.is_started(), "Thread already started.");
+	thread.start(_thread_func, this);
 }
 
 void EditorResourcePreview::stop() {
-	if (thread) {
+	if (thread.is_started()) {
 		exit = true;
 		preview_sem.post();
 		while (!exited) {
 			OS::get_singleton()->delay_usec(10000);
 			RenderingServer::get_singleton()->sync(); //sync pending stuff, as thread may be blocked on visual server
 		}
-		Thread::wait_to_finish(thread);
-		memdelete(thread);
-		thread = nullptr;
+		thread.wait_to_finish();
 	}
 }
 
 EditorResourcePreview::EditorResourcePreview() {
-	thread = nullptr;
 	singleton = this;
 	order = 0;
 	exit = false;
diff --git a/editor/editor_resource_preview.h b/editor/editor_resource_preview.h
index c119ccd99f..99c48967d8 100644
--- a/editor/editor_resource_preview.h
+++ b/editor/editor_resource_preview.h
@@ -70,7 +70,7 @@ class EditorResourcePreview : public Node {
 
 	Mutex preview_mutex;
 	Semaphore preview_sem;
-	Thread *thread;
+	Thread thread;
 	volatile bool exit;
 	volatile bool exited;
 
diff --git a/editor/fileserver/editor_file_server.cpp b/editor/fileserver/editor_file_server.cpp
index 02bbeb57c7..07edae833d 100644
--- a/editor/fileserver/editor_file_server.cpp
+++ b/editor/fileserver/editor_file_server.cpp
@@ -43,7 +43,7 @@ void EditorFileServer::_close_client(ClientData *cd) {
 	cd->connection->disconnect_from_host();
 	{
 		MutexLock lock(cd->efs->wait_mutex);
-		cd->efs->to_wait.insert(cd->thread);
+		cd->efs->to_wait.insert(&cd->thread);
 	}
 	while (cd->files.size()) {
 		memdelete(cd->files.front()->get());
@@ -278,7 +278,7 @@ void EditorFileServer::_thread_start(void *s) {
 				cd->connection = self->server->take_connection();
 				cd->efs = self;
 				cd->quit = false;
-				cd->thread = Thread::create(_subthread_start, cd);
+				cd->thread.start(_subthread_start, cd);
 			}
 		}
 
@@ -287,8 +287,7 @@ void EditorFileServer::_thread_start(void *s) {
 			Thread *w = self->to_wait.front()->get();
 			self->to_wait.erase(w);
 			self->wait_mutex.unlock();
-			Thread::wait_to_finish(w);
-			memdelete(w);
+			w->wait_to_finish();
 			self->wait_mutex.lock();
 		}
 		self->wait_mutex.unlock();
@@ -317,7 +316,7 @@ EditorFileServer::EditorFileServer() {
 	quit = false;
 	active = false;
 	cmd = CMD_NONE;
-	thread = Thread::create(_thread_start, this);
+	thread.start(_thread_start, this);
 
 	EDITOR_DEF("filesystem/file_server/port", 6010);
 	EDITOR_DEF("filesystem/file_server/password", "");
@@ -325,6 +324,5 @@ EditorFileServer::EditorFileServer() {
 
 EditorFileServer::~EditorFileServer() {
 	quit = true;
-	Thread::wait_to_finish(thread);
-	memdelete(thread);
+	thread.wait_to_finish();
 }
diff --git a/editor/fileserver/editor_file_server.h b/editor/fileserver/editor_file_server.h
index 267b129bda..e4c8327d76 100644
--- a/editor/fileserver/editor_file_server.h
+++ b/editor/fileserver/editor_file_server.h
@@ -47,7 +47,7 @@ class EditorFileServer : public Object {
 	};
 
 	struct ClientData {
-		Thread *thread = nullptr;
+		Thread thread;
 		Ref<StreamPeerTCP> connection;
 		Map<int, FileAccess *> files;
 		EditorFileServer *efs = nullptr;
@@ -61,7 +61,7 @@ class EditorFileServer : public Object {
 	static void _subthread_start(void *s);
 
 	Mutex wait_mutex;
-	Thread *thread;
+	Thread thread;
 	static void _thread_start(void *);
 	bool quit;
 	Command cmd;