[Vm-dev] win32 SetEvent, ResetEvent and MsgWaitForMultipleObjects

[Holger Freyther]

Hi Eliot, Bert,

as part of reading the "goToSleep" primitive I had a look at Windows and the last time I dealt with win32 API was quite some time ago so maybe I am wrong but doesn't the time slice below look like a race condition? If not what am I missing?



VM Thread			Socket Read Thread


ioRelinquishProcess..

 				 SIGNAL(pss->readSema)
				 -> SetEvent(vmWakeUpEvent)

ResetEvent(vmWakeUpEvent)
MsgWaitForMultipleObjects...




Couldn't we have lost the vmWakeUpEvent for the socket and then wait the full timeout? The history in Opensmalltalk-vm doesn't go far but couldn't we create the vmWakeUpEvent with the autoreset flag?


thank you

	holger


Code snippets:



sqInt ioRelinquishProcessorForMicroseconds(sqInt microSeconds)
{
        /* wake us up if something happens */
        ResetEvent(vmWakeUpEvent);
        if (WAIT_TIMEOUT ==
                MsgWaitForMultipleObjects(1, &vmWakeUpEvent, FALSE,
                            microSeconds / 1000, QS_ALLINPUT))



int synchronizedSignalSemaphoreWithIndex(int semaIndex)
{
  int result;

  /* Do our job - this is now synchronized in signalSemaphoreWithIndex */
  result = signalSemaphoreWithIndex(semaIndex);
  /* wake up interpret() if sleeping */
  SetEvent(vmWakeUpEvent);



static DWORD WINAPI readWatcherThread(privateSocketStruct *pss)
{
  struct timeval tv= { 1000, 0 }; /* Timeout value == 1000 sec */
  fd_set fds;
  int n, doWait;

  while(1) {
...
        switch(pss->readWatcherOp) {
        case WatchData:
          /* Data may be available */
          pss->sockState |= SOCK_DATA_READABLE;
          SIGNAL(pss->readSema);