pd.if.org Git - pdclib/blob - platform/win32/functions/threads/call_once.c

   1 #ifndef REGTEST
   2 #include <threads.h>
   3 #include <windows.h>
   4
   5 static volatile HANDLE onceHandle = NULL;
   6
   7 static void initOnceHandle( _PDCLIB_once_flag *flag )
   8 {
   9     HANDLE tOnceHandle = CreateEvent(NULL, TRUE, TRUE, NULL);
  10     HANDLE oldVal
  11         = InterlockedCompareExchangePointer(&flag->_Handle, tOnceHandle, NULL);
  12     if(oldVal != NULL)
  13         CloseHandle(tOnceHandle);
  14 }
  15
  16 void _PDCLIB_call_once(_PDCLIB_once_flag *flag, void (*func)(void))
  17 {
  18    if(!flag->_Handle) initOnceHandle(flag);
  19
  20    long oldVal = InterlockedCompareExchange(&flag->_State, 1, -1);
  21    for(;;) {
  22         if(oldVal == 0) {
  23             // Initialized
  24             return;
  25         } else if(oldVal == -1) {
  26             // We are doing the initialization
  27             func();
  28             if(InterlockedDecrement(&flag->_State) == 0)
  29                 CloseHandle(flag->_Handle);
  30             SetEvent(flag->_Handle);
  31             return;
  32         } else {
  33             // Somebody else is initializing - we are waiting
  34             long newOldVal = InterlockedCompareExchange(&flag->_State, oldVal,
  35                                                         oldVal+1);
  36             if(newOldVal == oldVal) {
  37                 // We incremented the "waiters" counter
  38                 if(WaitForSingleObject(flag->_Handle, INFINITE) != WAIT_OBJECT_0)
  39                     abort();
  40                 if(InterlockedDecrement(&flag->_State) == 0)
  41                     CloseHandle(flag->_Handle);
  42                 return;
  43             } else {
  44                 oldVal = newOldVal;
  45                 continue;
  46             }
  47         }
  48     }
  49 }
  50 #endif
  51
  52 #ifdef TEST
  53 #include "_PDCLIB_test.h"
  54
  55 #ifndef REGTEST
  56 static int count = 0;
  57 static once_flag once = ONCE_FLAG_INIT;
  58
  59 static void do_once(void)
  60 {
  61     count++;
  62 }
  63 #endif
  64
  65 int main( void )
  66 {
  67 #ifndef REGTEST
  68     TESTCASE(count == 0);
  69     call_once(&once, do_once);
  70     TESTCASE(count == 1);
  71     call_once(&once, do_once);
  72     TESTCASE(count == 1);
  73     do_once();
  74     TESTCASE(count == 2);
  75 #endif
  76     return TEST_RESULTS;
  77 }
  78
  79 #endif