Unexpected abort using GtkTextBuffer - c

Question

I am developing a Gtk based application where I need to update every X seconds a GtkTextBuffer, by concatenating the text that is already there. Apparently it succeeds but sometimes "randomly" the application aborts and I assume that it is due to this element, as it wasn't happening before. It sometimes aborts when there is a second/third update (each update only adds one new line) and sometimes it does not abort at all. I have based the TextBuffer update function on simple chat applications behavior but I don't know what I am doing wrong. The update function is:
void updateTextWindow(char *new_msg){
g_print("Msg rcv: %s\n", new_msg);
GtkTextIter start, end;
GtkTextBuffer *buffer = gtk_text_view_get_buffer (global_text_window);
//global_text_window is a global gtkwidget where TextBuffer is embedded
gchar *previous_text;
gtk_text_buffer_get_bounds (buffer, &start, &end);
previous_text = gtk_text_buffer_get_text (buffer, &start, &end, FALSE);
strcat(previous_text, "\n");
strcat(previous_text, new_msg);
gtk_text_buffer_set_text(buffer, previous_text, -1);
g_free(previous_text);
}
Moreover the related code in the main function where all GtkWidgets are declared and initializated is:
void create_ui (CustomData *data) {
[...]
GtkWidget *secondary_box; /* for text entry & buffer */
GtkScrolledWindow *scrolling_box;
GtkWidget *text_window;
GtkTextBuffer *buffer;
GtkWidget *text_entry;
secondary_box = gtk_box_new(GTK_ORIENTATION_VERTICAL, 1);
gtk_widget_set_size_request(secondary_box, 600, -1);
scrolling_box = gtk_scrolled_window_new(NULL, NULL);
gtk_scrolled_window_set_policy(scrolling_box, GTK_POLICY_NEVER, GTK_POLICY_AUTOMATIC);
text_entry = gtk_entry_new();
global_text_entry = text_entry;
gtk_entry_set_max_length(text_entry, 25);
text_window = gtk_text_view_new();
buffer = gtk_text_view_get_buffer(GTK_TEXT_VIEW(text_window));
gtk_text_buffer_set_text(buffer, "\n", -1);
gtk_text_view_set_editable(text_window, FALSE);
global_text_window = text_window;
gtk_scrolled_window_add_with_viewport(scrolling_box, text_window);
gtk_box_pack_end(GTK_CONTAINER(secondary_box), text_entry, FALSE, FALSE, 0);
g_signal_connect(G_OBJECT(text_entry), "activate", G_CALLBACK(text_entry_cb), &data);
gtk_box_pack_end(GTK_CONTAINER(secondary_box), scrolling_box, TRUE, TRUE, 0);
[...]
}
The update function is called from another thread, not from the "activate" callback for the text entry widget.
Thanks for your help

Answer 1

That code doesn't make sense. You're concatenating into a string that doesn't have space to hold more text, that's undefined behavior waiting to happen! Your posted answer doesn't make sense either, there's no point in creating a copy of the text like that. That might help just because it uses the heap a bit more, so perhaps you get luckier. Still undefined behavior to concatenate into previous_text.
If you want to append more text, there's no need to re-set the entire text contents. Just use gtk_text_buffer_insert() to insert new text at the end. Use gtk_text_buffer_get_iter_at_offset() first to get an iterator for the end of the buffer's contents.
UPDATE Oh, and also, you absolutely cannot call GTK+ from multiple threads. It is not a thread-safe library, so don't do that. It's a bit unclear if you do, but it sure sounds like it.