Prevent exit callback instance leaks

De-references pty_baton's exit callback after it is called so it can be
automatically released, preventing leaked instances.

Adds basic implementation for Pipe's get_status() method and forces PTY
to wait for child process to exit to ensure exit callback is cleaned up.

Adds a test to check that exit callback is still called as usual.

CHANGELOG.md

@@ -31,6 +31,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   `pipe.close()` method of the gdnative library is now registered.
 - Fixed 'Condition "!obj" is true.' error that would often print to console when
   closing terminals in the Terminal panel of the editor plugin.
+- Fixed leaked instances that would occur when PTY exited but child process was still
+  running.
 
 
 ## [v2.0.0](https://github.com/lihop/godot-xterm/compare/v1.2.1...v2.0.0) - 2021-07-25

addons/godot_xterm/native/src/node_pty/unix/pty.cc

@@ -445,8 +445,10 @@ static void pty_after_waitpid(uv_async_t *async) {
 
   Array argv = Array::make(baton->exit_code, baton->signal_code);
 
-  if (baton->cb != nullptr && baton->cb->is_valid())
+  if (baton->cb != nullptr && baton->cb->is_valid()) {
     baton->cb->call_funcv(argv);
+    baton->cb = (Ref<FuncRef>)nullptr;
+  }
 
   uv_close((uv_handle_t *)async, pty_after_close);
 }
@@ -669,4 +671,4 @@ void PTYUnix::_register_methods() {
   register_method("process", &PTYUnix::process);
 }
 
-void PTYUnix::_init() {}
+void PTYUnix::_init() {}

addons/godot_xterm/native/src/pipe.cpp

@@ -25,6 +25,7 @@ void Pipe::_register_methods() {
   register_method("poll", &Pipe::_poll_connection);
   register_method("open", &Pipe::open);
   register_method("write", &Pipe::write);
+  register_method("get_status", &Pipe::get_status);
   register_method("close", &Pipe::close);
 
   register_signal<Pipe>("data_received", "data",
@@ -56,11 +57,12 @@ godot_error Pipe::open(int fd, bool ipc = false) {
   RETURN_IF_UV_ERR(
       uv_read_start((uv_stream_t *)&handle, _alloc_buffer, _read_cb));
 
+  status = 1;
   return GODOT_OK;
 }
 
 void Pipe::close() {
-  uv_close((uv_handle_t *)&handle, NULL);
+  uv_close((uv_handle_t *)&handle, _close_cb);
   uv_run(uv_default_loop(), UV_RUN_NOWAIT);
 }
 
@@ -84,6 +86,8 @@ godot_error Pipe::write(String p_data) {
 }
 
 int Pipe::get_status() {
+  if (!uv_is_active((uv_handle_t *)&handle))
+    status = 0;
   _poll_connection();
   return status;
 }
@@ -120,3 +124,8 @@ void _alloc_buffer(uv_handle_t *handle, size_t suggested_size, uv_buf_t *buf) {
   buf->base = (char *)malloc(suggested_size);
   buf->len = suggested_size;
 }
+
+void _close_cb(uv_handle_t *handle) {
+  Pipe *pipe = static_cast<Pipe *>(handle->data);
+  pipe->status = 0;
+}

addons/godot_xterm/pty.gd

@@ -96,9 +96,10 @@ func open(cols: int = DEFAULT_COLS, rows: int = DEFAULT_ROWS) -> Array:
 
 
 func _exit_tree():
-	_exit_cb = null
 	if _pid > 1:
 		LibuvUtils.kill(_pid, Signal.SIGHUP)
+		while _pipe.get_status() != 0:
+			continue
 
 
 func _on_pipe_data_received(data):

test/platform/unix/unix.test.gd

@@ -73,6 +73,12 @@ func test_closes_pty_on_exit():
 	assert_eq(new_num_pts, num_pts)
 
 
+func test_emits_exited_signal_when_child_process_exits():
+	pty.call_deferred("fork", "exit")
+	yield(yield_to(pty, "exited", 1), YIELD)
+	assert_signal_emitted(pty, "exited")
+
+
 class Helper:
 	static func _get_pts() -> Array:
 		assert(false, "Abstract method")