c++ - Non blocking thread synchronization -

i have dialog box button, , other controls.

when button pressed worker thread spawned.

for easier discussion, let thread function lengthy job.

each time button clicked, new thread should spawn , stuff.

dialog box should not blocked while worker threads job, since user should able minimize it, click on other controls , on.

on wikipedia, have found term lock-free algorithm, refers non blocking thread synchronization.

this why interested in non blocking thread synchronization. believe ensure behavior need.

i new multithreading, did find articles/answered questions here, , have read documentation on microsoft it.

most of these use following algorithms:

1.

main thread declares volatile variable ( int or bool ) , passes worker thread. worker thread checks variable in loop, , if not set indicate termination, continues work. when needs terminated, parent thread sets variable.

2.

there vast documentation on microsoft's website synchronization. there, have found mutexes, critical sections, interlocks , more.

the problem these block parent thread ( waitforsingleobject or waitformultipleobjects api ), until worker thread finished.

also, searching here, have found recent question ( abort thread when dialog box close button clicked ) has helped me make start.

in order solve problem break question multiple ones, , post them separately, in order respect rules of stackoverflow.

so first question is:

which api/algorithm should use achieve non blocking thread synchronization, me achieve dialog box behaves described above ?

i appreciate links tutorials or code examples, if possible, since had no luck google ( also, developers learn best through code/pseudo code ).

i present initial tries these code snippets bellow, in case prove useful:

   // thread function     dword winapi mythread()    {        int result = 0;         //         if( /** ok **/ )            return result;        else        {            result = 1;              return result;        }    } 

now dialog box:

  // button clicked handler    case idc_button1:         {             // create thread              dword tid;              handle th = createthread( null , 0 ,                          (lpthread_start_routine)mythread ,                          null , 0 , &tid );              if( !th )                 enddialog( hwnd, idcancel );              closehandle( th );          }          break;     case idcancel:           enddialog( hwnd, idcancel );           break; 

at point, when run program, activate dialog box, , click on button, worker thread spawn up, , if wait finish.

yet if close dialog box early, nature of problem same in question have found here ( think waitformultipleobjects in idcancel handler can partialy fix leave post ).

edit #1:

i have posted new code, reflect progress , problems have faced.

important note:

instead of firing multiple threads, have hidden button starts thread, once pressed.

this means user have wait first thread finish, before he/she able activate second one.

this done easier debugging.

defined custom messages indicate if thread exited gracefully, or error happened.

    #define wm_thread_ok      ( wm_app + 1 )      #define wm_thread_error   ( wm_app + 2 ) 

added data structure passed thread can communicate dialog, , can aborted properly

    struct data     {         hwnd hwnd;          bool bcontinue;     }; 

reworked thread function send messages dialog box can notify dialog errors, or graceful end.

new code ( based on example book charles petzold-programming windows 5th ed. ):

   // thread function     dword winapi mythread( lpvoid lpvoid )    {         hresult hr;         volatile data *data = ( data* )lpvoid;         try        {           for( int = 0; < 10 && data->bcontinue; i++ )           {               hr = //                if( failed(hr) )                   throw _com_error(hr);           }            // once leave loop, check if thread aborted, or            if( ! ( data->bcontinue ) )           {               // thread aborted, cleanup , exit                // cleanup                return 0;           }            // if went well, cleanup, , "say" dialog box            // cleanup here            sendmessage( data->hwnd, wm_thread_ok, 0, 0 );            return 0; // exit gracefully        }        catch( _com_error & )        {            // cleanup             sendmessage( data->hwnd, wm_thread_error, 0, 0 );             return 1;        }    } 

here new code dialog box ( note: dialog box modeless ):

  static data data;    handle th = null;    // button clicked handler    case idc_button1:         {             // create thread              dword tid;              th = createthread( null , 0 ,                          (lpthread_start_routine)mythread ,                          (lpvoid)&data, 0 , &tid );              if( !th )                 destroywindow( hwnd );              // hide button activates thread              showwindow( getdlgitem( hwnd, idc_button1 ), sw_hide );          }          break;     case wm_thread_ok:       if( th )          closehandle( th );           showwindow( getdlgitem( hwnd, idc_button1 ), sw_show );       break;     case wm_thread_error:         if( th )            closehandle( threadhandle );         messagebox( hwnd, l"error", l"error", mb_iconerror );         break;     case idcancel:           data.bcontinue = false; // set thread abortion flag           if( th )          {             // after comment out below statement, thread aborts              // waitforsingleobject( th, infinite );              closehandle( th );          }           destroywindow( hwnd ); // dialog box modeless one!           break; 

my question is: there mistakes in code ? can improved, , how ?

thank you.

you dont need lock free synchronization. fire threads , have them signal objects when complete. non-blocking call on sync handle if dont want block ui thread

ie

waitformultipleobjects(n,lphandles, 0, 0); 

the last 0 says return rather wait if object(s) not signalled