How to use Fl::awake in the FLTK Library - c++

Question

I would like to use the Fl::awake(callback) function to call functions from my main loop in an FLTK program. I am calling Fl::awake from a child thread, it returns 1 (success), but my function never gets called. I am calling Fl::wait() in a loop in the main thread. Is there any way i can troubleshoot this?

Answer 1

Code below is an example of a relatively simple FLTK 1.3 application which uses Fl::awake(callback) . The code is from the FLTK's test directory. Just fetch the source, and you'll find numerous examples. You did not give us your code, but I assume you did not call Fl::lock(), and later Fl::unlock() in your thread. It is essential because you should not access widgets outside that section...
include
#if HAVE_PTHREAD || defined(WIN32)
# include <FL/Fl.H>
# include <FL/Fl_Double_Window.H>
# include <FL/Fl_Browser.H>
# include <FL/Fl_Value_Output.H>
# include <FL/fl_ask.H>
# include "threads.h"
# include <stdio.h>
# include <math.h>
Fl_Thread prime_thread;
Fl_Browser *browser1, *browser2;
Fl_Value_Output *value1, *value2;
int start2 = 3;
void magic_number_cb(void *p)
{
Fl_Value_Output *w = (Fl_Value_Output*)p;
w->labelcolor(FL_RED);
w->redraw_label();
}
void* prime_func(void* p)
{
Fl_Browser* browser = (Fl_Browser*) p;
Fl_Value_Output *value;
int n;
int step;
char proud = 0;
if (browser == browser2) {
n = start2;
start2 += 2;
step = 12;
value = value2;
} else {
n = 3;
step = 2;
value = value1;
}
// very simple prime number calculator !
//
// The return at the end of this function can never be reached and thus
// will generate a warning with some compilers, however we need to have
// a return statement or other compilers will complain there is no return
// statement. To avoid warnings on all compilers, we fool the smart ones
// into beleiving that there is a chance that we reach the end by testing
// n>=0, knowing that logically, n will never be negative in this context.
if (n>=0) for (;;) {
int pp;
int hn = (int)sqrt((double)n);
for (pp=3; pp<=hn; pp+=2) if ( n%pp == 0 ) break;
if (pp >= hn) {
char s[128];
sprintf(s, "%d", n);
// Obtain a lock before we access the browser widget...
Fl::lock();
browser->add(s);
browser->bottomline(browser->size());
if (n > value->value()) value->value(n);
n += step;
// Release the lock...
Fl::unlock();
// Send a message to the main thread, at which point it will
// process any pending redraws for our browser widget. The
// message we pass here isn't used for anything, so we could also
// just pass NULL.
Fl::awake(p);
if (n>10000 && !proud) {
proud = 1;
Fl::awake(magic_number_cb, value);
}
} else {
// This should not be necessary since "n" and "step" are local variables,
// however it appears that at least MacOS X has some threading issues
// that cause semi-random corruption of the (stack) variables.
Fl::lock();
n += step;
Fl::unlock();
}
}
return 0L;
}
int main(int argc, char **argv)
{
Fl_Double_Window* w = new Fl_Double_Window(200, 200, "Single Thread");
browser1 = new Fl_Browser(0, 0, 200, 175);
w->resizable(browser1);
value1 = new Fl_Value_Output(100, 175, 200, 25, "Max Prime:");
w->end();
w->show(argc, argv);
w = new Fl_Double_Window(200, 200, "Six Threads");
browser2 = new Fl_Browser(0, 0, 200, 175);
w->resizable(browser2);
value2 = new Fl_Value_Output(100, 175, 200, 25, "Max Prime:");
w->end();
w->show();
browser1->add("Prime numbers:");
browser2->add("Prime numbers:");
// Enable multi-thread support by locking from the main
// thread. Fl::wait() and Fl::run() call Fl::unlock() and
// Fl::lock() as needed to release control to the child threads
// when it is safe to do so...
Fl::lock();
// Start threads...
// One thread displaying in one browser
fl_create_thread(prime_thread, prime_func, browser1);
// Several threads displaying in another browser
fl_create_thread(prime_thread, prime_func, browser2);
fl_create_thread(prime_thread, prime_func, browser2);
fl_create_thread(prime_thread, prime_func, browser2);
fl_create_thread(prime_thread, prime_func, browser2);
fl_create_thread(prime_thread, prime_func, browser2);
fl_create_thread(prime_thread, prime_func, browser2);
Fl::run();
return 0;
}
#else
# include <FL/fl_ask.H>
int main() {
fl_alert("Sorry, threading not supported on this platform!");
}
#endif // HAVE_PTHREAD || WIN32