[core_bind] Add `Thread::is_alive`

core/bind/core_bind.cpp

@@ -2680,12 +2680,15 @@ void _Thread::_start_func(void *ud) {
 			}
 		}
 
+		t->running.clear();
 		ERR_FAIL_MSG("Could not call function '" + t->target_method.operator String() + "' to start thread " + t->get_id() + ": " + reason + ".");
 	}
+
+	t->running.clear();
 }
 
 Error _Thread::start(Object *p_instance, const StringName &p_method, const Variant &p_userdata, Priority p_priority) {
-	ERR_FAIL_COND_V_MSG(active.is_set(), ERR_ALREADY_IN_USE, "Thread already started.");
+	ERR_FAIL_COND_V_MSG(is_active(), ERR_ALREADY_IN_USE, "Thread already started.");
 	ERR_FAIL_COND_V(!p_instance, ERR_INVALID_PARAMETER);
 	ERR_FAIL_COND_V(p_method == StringName(), ERR_INVALID_PARAMETER);
 	ERR_FAIL_INDEX_V(p_priority, PRIORITY_MAX, ERR_INVALID_PARAMETER);
@@ -2694,7 +2697,7 @@ Error _Thread::start(Object *p_instance, const StringName &p_method, const Varia
 	target_method = p_method;
 	target_instance_id = p_instance->get_instance_id();
 	userdata = p_userdata;
-	active.set();
+	running.set();
 
 	Ref<_Thread> *ud = memnew(Ref<_Thread>(this));
 
@@ -2710,16 +2713,20 @@ String _Thread::get_id() const {
 }
 
 bool _Thread::is_active() const {
-	return active.is_set();
+	return thread.is_started();
 }
+
+bool _Thread::is_alive() const {
+	return running.is_set();
+}
+
 Variant _Thread::wait_to_finish() {
-	ERR_FAIL_COND_V_MSG(!active.is_set(), Variant(), "Thread must be active to wait for its completion.");
+	ERR_FAIL_COND_V_MSG(!is_active(), Variant(), "Thread must have been started to wait for its completion.");
 	thread.wait_to_finish();
 	Variant r = ret;
 	target_method = StringName();
 	target_instance_id = ObjectID();
 	userdata = Variant();
-	active.clear();
 
 	return r;
 }
@@ -2728,6 +2735,7 @@ void _Thread::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("start", "instance", "method", "userdata", "priority"), &_Thread::start, DEFVAL(Variant()), DEFVAL(PRIORITY_NORMAL));
 	ClassDB::bind_method(D_METHOD("get_id"), &_Thread::get_id);
 	ClassDB::bind_method(D_METHOD("is_active"), &_Thread::is_active);
+	ClassDB::bind_method(D_METHOD("is_alive"), &_Thread::is_alive);
 	ClassDB::bind_method(D_METHOD("wait_to_finish"), &_Thread::wait_to_finish);
 
 	BIND_ENUM_CONSTANT(PRIORITY_LOW);
@@ -2739,7 +2747,7 @@ _Thread::_Thread() {
 }
 
 _Thread::~_Thread() {
-	ERR_FAIL_COND_MSG(active.is_set(), "Reference to a Thread object was lost while the thread is still running...");
+	ERR_FAIL_COND_MSG(is_active(), "Reference to a Thread object was lost while the thread is still running...");
 }
 
 /////////////////////////////////////

core/bind/core_bind.h

@@ -683,7 +683,7 @@ class _Thread : public Reference {
 protected:
 	Variant ret;
 	Variant userdata;
-	SafeFlag active;
+	SafeFlag running;
 	ObjectID target_instance_id;
 	StringName target_method;
 	Thread thread;
@@ -702,6 +702,7 @@ public:
 	Error start(Object *p_instance, const StringName &p_method, const Variant &p_userdata = Variant(), Priority p_priority = PRIORITY_NORMAL);
 	String get_id() const;
 	bool is_active() const;
+	bool is_alive() const;
 	Variant wait_to_finish();
 
 	_Thread();

doc/classes/Thread.xml

@@ -22,7 +22,14 @@
 		<method name="is_active" qualifiers="const">
 			<return type="bool" />
 			<description>
-				Returns [code]true[/code] if this [Thread] is currently active. An active [Thread] cannot start work on a new method but can be joined with [method wait_to_finish].
+				Returns [code]true[/code] if this [Thread] has been started. Once started, this will return [code]true[/code] until it is joined using [method wait_to_finish]. For checking if a [Thread] is still executing its task, use [method is_alive].
+			</description>
+		</method>
+		<method name="is_alive" qualifiers="const">
+			<return type="bool" />
+			<description>
+				Returns [code]true[/code] if this [Thread] is currently running. This is useful for determining if [method wait_to_finish] can be called without blocking the calling thread.
+				To check if a [Thread] is joinable, use [method is_active].
 			</description>
 		</method>
 		<method name="start">
@@ -39,8 +46,9 @@
 		<method name="wait_to_finish">
 			<return type="Variant" />
 			<description>
-				Joins the [Thread] and waits for it to finish. Returns what the method called returned.
+				Joins the [Thread] and waits for it to finish. Returns the output of the method passed to [method start].
 				Should either be used when you want to retrieve the value returned from the method called by the [Thread] or before freeing the instance that contains the [Thread].
+				To determine if this can be called without blocking the calling thread, check if [method is_alive] is [code]false[/code].
 				[b]Note:[/b] After the [Thread] finishes joining it will be disposed. If you want to use it again you will have to create a new instance of it.
 			</description>
 		</method>