如何在 FLTK 库中使用 Fl::awake

Posted 2023-02-21

【中文标题】如何在 FLTK 库中使用 Fl::awake

【英文标题】：How to use Fl::awake in the FLTK Library

【发布时间】：2011-11-09 17:42:05

【问题描述】：

我想使用 Fl::awake(callback) 函数在 FLTK 程序中从我的主循环调用函数。我从子线程调用 Fl::awake，它返回 1（成功），但我的函数永远不会被调用。我在主线程的循环中调用 Fl::wait() 。有什么办法可以解决这个问题吗？

【参考方案1】：

下面的代码是一个使用 Fl::awake(callback) 的相对简单的 FLTK 1.3 应用程序示例。代码来自 FLTK 的测试目录。只需获取源代码，您就会发现许多示例。你没有给我们你的代码，但我假设你没有在你的线程中调用Fl::lock()，后来又调用了Fl::unlock()。这是必不可少的，因为您不应访问该部分之外的小部件...

包括

#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

【讨论】：

我实际上不调用 lock 和 unlock 因为我不访问主线程之外的小部件。我只是使用 awake 作为信号机制。不过，main 中的 lock 调用可以修复它，感谢您为我指明正确的方向。

注意：这段代码让“处理”线程在后台运行，同时让 GUI 仍然响应，但是这个实现可以让处理线程被无响应的 GUI 挂起。例如，如果您调整窗口大小并在调整大小时只是拖动鼠标，质数的计算将停止，直到您停止创建 GUI 事件。调用 Fl::awake() 并不能避免该问题，因为您仍然需要锁定/解锁以使主线程注意到 awake() 事件。所以，如果你想让你的“处理”线程不受 GUI 的影响，你就不能进行任何 FLTK 调用。

有点不相关，但让我补充一下：在 main 函数中调用 Fl::lock() 非常重要。 我试图编写一个没有该调用的程序，它由于争用而无法正常工作。