Using multiple threads with GTK? - c

Question

How do I use multiple threads in GTK? I have 2 threads, one initializes the GUI and then continuously runs gtk_main() to draw my gui and my other thread does all my program logic and computing, however when my program logic thread updates a GtkImage it will randomly and inconsistently stop updating and freeze and will not draw the anything on the form anymore.
I have read and been told to only call GTK functions from the gtk thread but that is impossible as once you call gtk_main() it will be stuck there until the program exits.
Anyone know how I can get my program and gui cooperating together and show me an example of how it would work with my existing program?
I have been stuck on this for hours now and need to finish this script for a company soon so they can use it to help automate one of their tasks at their manufacturing facility.
Ex.
static GtkWidget* gtk_image;
void my_thread()
{
while (1) {
//wait for input
//do program logic
//update gtk_image to new image
}
}
void gui_thread() {
//initialize gui
//call gtk_main //it never exits this function until program is closed so you can see how its impossible to make any drawing calls from this thread
}
my actual code looks like this (where cam_main and main_gtk are the threads I was mentioning):
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdarg.h>
#include <gphoto2/gphoto2-camera.h>
#include <gphoto2/gphoto2-context.h>
#include <wiringPi.h>
#include <gtk/gtk.h>
#include <pthread.h>
//program
static int running = 1;
//libgphoto2
static CameraList* list;
static Camera** cams;
static GPContext* context;
static const char *name, *value;
static int ret, count;
static int pic = 0;
static int front = 1;
static const char* workingDir;
//GTK
static GtkWidget *window, *vbox,*hboxDir, *hboxCamLabels, *hboxFrontPics, *hboxBackPics, *hboxStatus, *lblDir, *btnConfigDir, *lblCams, *lblFront, *lblBack, *lblCurrentStatus;
static GtkWidget *front_cams[3];
static GtkWidget *back_cams[3];
static GdkPixbuf *pxbscaled = NULL;
static GdkPixbuf *pixbuf = NULL;
static GError* err = NULL;
static void btnConfigDir_ConfigureDirectory(GtkWidget* widget, gpointer data) {
GtkWidget *dialog;
GtkFileChooserAction action = GTK_FILE_CHOOSER_ACTION_OPEN;
gint res;
dialog = gtk_file_chooser_dialog_new ("Open File", window,
action,
"_Cancel",
GTK_RESPONSE_CANCEL,
"_Open",
GTK_RESPONSE_ACCEPT,
NULL);
res = gtk_dialog_run (GTK_DIALOG (dialog));
if (res == GTK_RESPONSE_ACCEPT)
{
char *filename;
GtkFileChooser *chooser = GTK_FILE_CHOOSER (dialog);
workingDir = gtk_file_chooser_get_filename (chooser);
}
//gtk_label_set_text((GTK_LABEL)lblDir, workingDir);
gtk_widget_destroy (dialog);
}
void* main_gtk() {
//GTK WIDGET QUEUE REDRAW WOULD REDRAW AT APPROPRIATE TIME
//INIT GTK
gtk_init(NULL, NULL);
//SETUP WINDOW
window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
//button1=gtk_button_new_with_label("Click me");
//gtk_button_set_label(GTK_BUTTON(button1), "click me 1");
g_signal_connect(window,"delete-event", G_CALLBACK(gtk_main_quit), NULL);
workingDir = "/media/pi/SD CARD";
lblDir = gtk_label_new("Save to: dir\t");
btnConfigDir = gtk_button_new_with_label("Configure Directory");
g_signal_connect(btnConfigDir, "clicked", G_CALLBACK(btnConfigDir_ConfigureDirectory), NULL);
lblCams = gtk_label_new("\t\t\t\t\t\t\t\tCAM 1\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\tCAM2\t\t\t\t\t\t\t\t\t\t\t\t\t\t\tCAM3");
lblFront = gtk_label_new("Front");
lblBack = gtk_label_new("Back ");
lblCurrentStatus = gtk_label_new("Current Status: Idle");
//SET WINDOW SIZE AND TITLE
//gtk_widget_set_size_request(window, 600, 400);
gtk_window_set_title(GTK_WINDOW(window), "CaptureGui");
//RESIZE IMAGES
//image
front_cams[0] = gtk_image_new();
front_cams[1] = gtk_image_new();
front_cams[2] = gtk_image_new();
back_cams[0] = gtk_image_new();
back_cams[1] = gtk_image_new();
back_cams[2] = gtk_image_new();
GdkPixbuf* pxb;
pxb = gdk_pixbuf_new(0, 0, 8, 500, 300);
gtk_image_set_from_pixbuf(GTK_IMAGE(front_cams[0]), pxb);
gtk_image_set_from_pixbuf(GTK_IMAGE(front_cams[1]), pxb);
gtk_image_set_from_pixbuf(GTK_IMAGE(front_cams[2]), pxb);
gtk_image_set_from_pixbuf(GTK_IMAGE(back_cams[0]), pxb);
gtk_image_set_from_pixbuf(GTK_IMAGE(back_cams[1]), pxb);
gtk_image_set_from_pixbuf(GTK_IMAGE(back_cams[2]), pxb);
//g_print("1");
//front_cams[0] = gtk_image_new_from_file("/media/pi/SD CARD/cam-1_0_a_front.jpg");
//set_image_scaled(front_cams[0], "/media/pi/SD CARD/cam-1_1_a_front.jpg");
//set_image_scaled(front_cams[1], "/media/pi/SD CARD/cam-1_1_a_front.jpg");
//set_image_scaled(front_cams[2], "/media/pi/SD CARD/cam-1_1_b_back.jpg");
//PACK
hboxDir = gtk_box_new(0, 0);
hboxCamLabels = gtk_box_new(0, 0);
hboxFrontPics = gtk_box_new(0, 0);
hboxBackPics = gtk_box_new(0, 0);
hboxStatus = gtk_box_new(0, 0);
vbox = gtk_vbox_new(0, 10);
gtk_box_pack_end(GTK_BOX(hboxDir), btnConfigDir, 0, 0, 0);
gtk_box_pack_end(GTK_BOX(hboxDir), lblDir, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(hboxCamLabels), lblCams, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(hboxFrontPics), lblFront, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(hboxFrontPics), front_cams[0], 0, 0, 10);
gtk_box_pack_start(GTK_BOX(hboxFrontPics), front_cams[1], 0, 0, 10);
gtk_box_pack_start(GTK_BOX(hboxFrontPics), front_cams[2], 0, 0, 10);
gtk_box_pack_start(GTK_BOX(hboxBackPics), lblBack, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(hboxBackPics), back_cams[0], 0, 0, 10);
gtk_box_pack_start(GTK_BOX(hboxBackPics), back_cams[1], 0, 0, 10);
gtk_box_pack_start(GTK_BOX(hboxBackPics), back_cams[2], 0, 0, 10);
gtk_box_pack_start(GTK_BOX(hboxStatus), lblCurrentStatus, 0, 0, 10);
gtk_box_pack_start(GTK_BOX(vbox), hboxDir, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(vbox), hboxCamLabels, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(vbox), hboxFrontPics, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(vbox), hboxBackPics, 0, 0, 0);
gtk_box_pack_start(GTK_BOX(vbox), hboxStatus, 0, 0, 0);
//gtk_box_pack_start(GTK_BOX(hbox), front_cams[0], 0, 0, 0);
//gtk_box_pack_start(GTK_BOX(hbox), front_cams[1], 0, 0, 0);
//gtk_box_pack_start(GTK_BOX(hbox), front_cams[2], 0, 0, 0);
//gtk_box_pack_start(GTK_BOX(hbox), back_cams[0], 0, 0, 0);
//gtk_box_pack_start(GTK_BOX(hbox), back_cams[1], 0, 0, 0);
//gtk_box_pack_start(GTK_BOX(hbox), back_cams[2], 0, 0, 0);
gtk_container_add(GTK_CONTAINER(window), vbox);
//ADD ELEMENTS TO GUI
//gtk_container_add(GTK_CONTAINER(window), image1);
//gtk_container_add(GTK_CONTAINER(window), image2);
//image2 = gtk_image_new_from_file("/media/pi/SD CARD/cam-1_0_b_back.jpg");
//gtk_container_add(GTK_CONTAINER(window), image2);
//SHOW GUI
gtk_widget_show_all(window);
gtk_main();
}
void set_image_scaled(GtkWidget* img, const char* path) {
pixbuf = gdk_pixbuf_new_from_file(path, &err);
g_assert_no_error(err);
pxbscaled = gdk_pixbuf_scale_simple(pixbuf, 500, 300, GDK_INTERP_BILINEAR);
gtk_image_set_from_pixbuf(GTK_IMAGE(img), pxbscaled);
g_object_unref(pixbuf);
g_object_unref(pxbscaled);
}
void* cam_main() {
while (running == 1) {
if (digitalRead(4) == 0)
{
printf("taking pics of %s item %i\n", (front == 1) ? "front" : "back", pic);
for (int i = 0; i < count; i++)
{
int fd, retval;
CameraFile *file;
CameraFilePath cfPath;
strcpy(cfPath.folder, "/");
strcpy(cfPath.name, "foo1.jpg");
printf("Capturing cam%i...\n", i + 1);
int res = gp_camera_capture(cams[i], GP_CAPTURE_IMAGE, &cfPath, context);
//printf(gp_port_result_as_string(res));
printf("capture result: %i\n", res);
//Camera won't take pic if busy and will continue to program end
char buf[256];
snprintf(buf, sizeof(buf), "%s/cam-%i_%i_%s.jpg", workingDir, i + 1, pic, (front == 1) ? "a_front" : "b_back"); //a_ to make front come before back otherwise systems will order incorrectly
fd = open(buf, O_CREAT | O_WRONLY, 0644);
retval = gp_file_new_from_fd(&file, fd);
retval = gp_camera_file_get(cams[i], cfPath.folder, cfPath.name, GP_FILE_TYPE_NORMAL, file, context);
retval = gp_camera_file_delete(cams[i], cfPath.folder, cfPath.name, context);
gp_file_free(file);
//debug
//if (front == 1 && i == 0)
// set_image_scaled(front_cams[0], buf);
if (front == 1)
set_image_scaled(front_cams[i], buf);
else
set_image_scaled(back_cams[i], buf);
}
if (front == 1)
front = 0;
else
{
front = 1;
pic += 1;
}
printf("pics taken...\n");
}
}
}
int main(int argc, char **argv)
{
//Kill any processes using cams
system("pkill -f gphoto2");
//Wiring pi init
wiringPiSetupGpio();
//Init
context = gp_context_new();
detect_cams();
pthread_t logic_thread_handle, gui_thread_handle;
pthread_create(&logic_thread_handle, NULL, cam_main, NULL);
pthread_create(&gui_thread_handle, NULL, main_gtk, NULL);
pthread_join(gui_thread_handle, 0);
pthread_join(logic_thread_handle, 0);
//Deinit
for (int i = 0; i < count; i++)
{
gp_camera_exit(cams[i], context);
gp_camera_free(cams[i]);
}
return 0;
}
void detect_cams() {
//Detecting all cameras and loading them into mem
//Detecting all cameras
ret = gp_list_new(&list);
if (ret < GP_OK) return 1;
gp_list_reset(list);
count = gp_camera_autodetect(list, context);
if (count < 1)
{
printf("No cameras detected.\n");
return 1;
}
//Open all cameras
printf("Number of cameras: %d\n", count);
cams = calloc(sizeof (Camera*), count);
for (int i = 0; i < count; i++)
{
gp_list_get_name(list, i, &name);
gp_list_get_value(list, i, &value);
ret = open_cam(&cams[i], name, value, context);
if (ret < GP_OK)
fprintf(stderr, "Camera %s on port %s failed to open\n", name, value);
}
}
int open_cam(Camera ** camera, const char *model, const char *port, GPContext *context) {
GPPortInfoList *portinfolist = NULL;
CameraAbilitiesList *abilities = NULL;
int ret, m, p;
CameraAbilities a;
GPPortInfo pi;
ret = gp_camera_new (camera);
if (ret < GP_OK) return ret;
if (!abilities) {
/* Load all the camera drivers we have... */
ret = gp_abilities_list_new (&abilities);
if (ret < GP_OK) return ret;
ret = gp_abilities_list_load (abilities, context);
if (ret < GP_OK) return ret;
}
/* First lookup the model / driver */
m = gp_abilities_list_lookup_model (abilities, model);
if (m < GP_OK) return ret;
ret = gp_abilities_list_get_abilities (abilities, m, &a);
if (ret < GP_OK) return ret;
ret = gp_camera_set_abilities (*camera, a);
if (ret < GP_OK) return ret;
if (!portinfolist) {
/* Load all the port drivers we have... */
ret = gp_port_info_list_new (&portinfolist);
if (ret < GP_OK) return ret;
ret = gp_port_info_list_load (portinfolist);
if (ret < 0) return ret;
ret = gp_port_info_list_count (portinfolist);
if (ret < 0) return ret;
}
/* Then associate the camera with the specified port */
p = gp_port_info_list_lookup_path (portinfolist, port);
switch (p) {
case GP_ERROR_UNKNOWN_PORT:
fprintf (stderr, "The port you specified "
"('%s') can not be found. Please "
"specify one of the ports found by "
"'gphoto2 --list-ports' and make "
"sure the spelling is correct "
"(i.e. with prefix 'serial:' or 'usb:').",
port);
break;
default:
break;
}
if (p < GP_OK) return p;
ret = gp_port_info_list_get_info (portinfolist, p, &pi);
if (ret < GP_OK) return ret;
ret = gp_camera_set_port_info (*camera, pi);
if (ret < GP_OK) return ret;
return GP_OK;
}

Answer 1

I have read and been told to only call GTK functions from the gtk thread but that is impossible as once you call gtk_main() it will be stuck there until the program exits.
No, it's not impossible. Control is returned to your program even while gtk_main() is active, by means of callbacks. In your thread, you can schedule a callback to be called in the GTK thread using gdk_threads_add_idle(). See GTK3 and multithreading, replacing deprecated functions for more information.