[core_bind] Add `is_alive` to Thread. Replace `is_active` with `is_started`.

Replacing `is_active` resolves an API discrepancy between core_bind Thread and core/os Thread.

core/core_bind.cpp

@@ -1771,6 +1771,7 @@ void Thread::_start_func(void *ud) {
 
 	Object *target_instance = t->target_callable.get_object();
 	if (!target_instance) {
+		t->running.clear();
 		ERR_FAIL_MSG(vformat("Could not call function '%s' on previously freed instance to start thread %s.", t->target_callable.get_method(), t->get_id()));
 	}
 
@@ -1813,19 +1814,22 @@ void Thread::_start_func(void *ud) {
 
 	t->target_callable.call(arg, argc, t->ret, ce);
 	if (ce.error != Callable::CallError::CALL_OK) {
+		t->running.clear();
 		ERR_FAIL_MSG("Could not call function '" + t->target_callable.get_method().operator String() + "' to start thread " + t->get_id() + ": " + Variant::get_callable_error_text(t->target_callable, arg, argc, ce) + ".");
 	}
+
+	t->running.clear();
 }
 
 Error Thread::start(const Callable &p_callable, 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_started(), ERR_ALREADY_IN_USE, "Thread already started.");
 	ERR_FAIL_COND_V(p_callable.is_null(), ERR_INVALID_PARAMETER);
 	ERR_FAIL_INDEX_V(p_priority, PRIORITY_MAX, ERR_INVALID_PARAMETER);
 
 	ret = Variant();
 	target_callable = p_callable;
 	userdata = p_userdata;
-	active.set();
+	running.set();
 
 	Ref<Thread> *ud = memnew(Ref<Thread>(this));
 
@@ -1840,15 +1844,18 @@ String Thread::get_id() const {
 	return itos(thread.get_id());
 }
 
-bool Thread::is_active() const {
-	return active.is_set();
+bool Thread::is_started() const {
+	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_started(), Variant(), "Thread must have been started to wait for its completion.");
 	thread.wait_to_finish();
 	Variant r = ret;
-	active.clear();
 	target_callable = Callable();
 	userdata = Variant();
 
@@ -1858,7 +1865,8 @@ Variant Thread::wait_to_finish() {
 void Thread::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("start", "callable", "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_started"), &Thread::is_started);
+	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);

core/core_bind.h

@@ -538,7 +538,7 @@ class Thread : public RefCounted {
 protected:
 	Variant ret;
 	Variant userdata;
-	SafeFlag active;
+	SafeFlag running;
 	Callable target_callable;
 	::Thread thread;
 	static void _bind_methods();
@@ -554,7 +554,8 @@ public:
 
 	Error start(const Callable &p_callable, const Variant &p_userdata = Variant(), Priority p_priority = PRIORITY_NORMAL);
 	String get_id() const;
-	bool is_active() const;
+	bool is_started() const;
+	bool is_alive() const;
 	Variant wait_to_finish();
 };
 

doc/classes/Thread.xml

@@ -19,10 +19,17 @@
 				Returns the current [Thread]'s ID, uniquely identifying it among all threads. If the [Thread] is not running this returns an empty string.
 			</description>
 		</method>
-		<method name="is_active" qualifiers="const">
+		<method name="is_alive" 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] 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_started].
+			</description>
+		</method>
+		<method name="is_started" qualifiers="const">
+			<return type="bool" />
+			<description>
+				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="start">
@@ -31,15 +38,16 @@
 			<argument index="1" name="userdata" type="Variant" default="null" />
 			<argument index="2" name="priority" type="int" enum="Thread.Priority" default="1" />
 			<description>
-				Starts a new [Thread] that calls [code]callable[/code] with [code]userdata[/code] passed as an argument. Even if no userdata is passed, [code]method[/code] must accept one argument and it will be null. The [code]priority[/code] of the [Thread] can be changed by passing a value from the [enum Priority] enum.
+				Starts a new [Thread] that calls [code]callable[/code] with [code]userdata[/code] passed as an argument. Even if no userdata is passed, [code]callable[/code] must accept one argument and it will be null. The [code]priority[/code] of the [Thread] can be changed by passing a value from the [enum Priority] enum.
 				Returns [constant OK] on success, or [constant ERR_CANT_CREATE] on failure.
 			</description>
 		</method>
 		<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 [Callable] 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>