Re: [PATCH] Windows jobserver updates for GNU make 4.1

[Eli Zaretskii]

> From: Troy Runkel <address@hidden>
> Date: Wed, 24 Feb 2016 17:27:57 +0000
> Cc: Troy Runkel <address@hidden>
> 
> This patch expands the maximum number of simultaneous jobs on Windows from 63 
> (limit dictated by
> Windows MAXIMUM_WAIT_OBJECTS) to 4095.
> 
> It also fixes a situation where GNU make on Windows could deadlock and/or 
> suffer memory corruption issues
> if –j or –j63 was used. The problem was due to the way that $(shell …) 
> commands are handled.

Thanks.

I wonder how hard would it be to remove the limitation altogether?
If we are lifting the limitation, why not lift it entirely?

Another comment is about the busy-wait loop (with 10-msec sleep) that
this change uses -- it looks like, when there are 4095 jobs running,
we will be re-checking each process once every 640 msec, is that
right?  That might be too large a delay, I think.  Did you consider a
design that uses a separate thread for watching up to 64 processes?  I
think such a design might scale up better; in particular, the response
time for checking the status of each job will not decrease as the
number of jobs goes up.

> +DWORD GmakeWaitForMultipleObjects(
> +  DWORD nCount,
> +  const HANDLE *lpHandles,
> +  BOOL bWaitAll,
> +  DWORD dwMilliseconds
> +)
> +{
> +  assert(nCount <= GMAKE_MAXIMUM_WAIT_OBJECTS);
> +
> +  if (nCount <= MAXIMUM_WAIT_OBJECTS) {
> +    DWORD retVal =  WaitForMultipleObjects(nCount, lpHandles, bWaitAll, 
> dwMilliseconds);
> +    return (retVal == WAIT_TIMEOUT) ? GMAKE_WAIT_TIMEOUT : retVal;

This GMAKE_WAIT_TIMEOUT and GMAKE_WAIT_ABANDONED_0 stuff looks like a
kludge to me; can we get rid of it?

> +        switch (retVal) {
> +          case WAIT_TIMEOUT:
> +            retVal = GMAKE_WAIT_TIMEOUT;
> +            continue;
> +            break;
> +          case WAIT_FAILED:
> +            fprintf(stderr,"WaitForMultipleOjbects failed waiting with error 
> %d\n", GetLastError());
> +            break;

I guess this fprintf should go away, or be converted to a DB call?

Thank you for working on this.