Creating gtk signal for editing GtkWidget running in other thread

Question

I have an app, which basically runs in terminal mode, but it can open it's GUI part in another thread (Simple window with a GtkTextView to print some messages out). I need to manually update the contents of this GtkTextView when some event happens in main thread. For that purpose I created a 'new-message-received' signal which should pass a pointer to char array msg with message to print

Creating new signal:

g_signal_new("new-message-received", G_TYPE_OBJECT, G_SIGNAL_RUN_FIRST, 0, NULL, NULL, g_cclosure_marshal_VOID__POINTER, G_TYPE_NONE, 1, G_TYPE_POINTER);

Connecting it with handler function:

g_signal_connect(G_OBJECT(demo_window), "new-message-received", G_CALLBACK(print_demo_message),(gpointer)msg);

And emitting signal:

if (flag){ memset(msg, 0, 256); g_signal_emit_by_name(G_OBJECT(demo_window), "new-message-received", (gpointer) msg); ... }

The problem is that signal handler gets some broken pointer (I try to print it to stdout -- it's always some random 4 symbols) instead of passed message. The handler is:

void print_demo_message(gpointer *param) { const gchar* message = (const gchar*)param; g_print("Got message: %s\n", message); ... }

The output is like:

Got message: p��

What I tried:

Making msg a global variable to avoid re-initialization -- no result
Using a generic marshaller in signal creating -- no result
Passing a link to msg address instead of a pointer to it, no result too.

The question is -- what am I doing wrong?

Thanks in advance.

Lexx129 · Accepted Answer · 2018-05-22 12:55:49Z

Had to solve this myself, there was no need in using signals at all.

Main thread for GTK is a thread, where gtk_main() is called from. Accessing any GTK object outside it's main thread is forbidden. So, to initiate a thread for GTK GUI I used g_thread_new() and g_idle_add(print_demo_message, msg) to "ask" GTK main thread to paste the msg to GtkTextView.

So, now it look like this:

APP MAIN THREAD: if(%some_condition%){ msg = malloc(256); sprintf(msg, "Some text"); g_idle_add(print_demo_message, msg); }

GUI THREAD: boolean print_demo_message(gpointer data) { gchar* message = data; g_print("Got message: %s\n", message); ... }

Message transferred OK, works like charm :)

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