Re: GMAKE 3.81 vs GMAKE 4.2

[Paul Smith]

On Wed, 2019-12-04 at 18:14 +0530, nikhil jain wrote:
> Just for information.
> 
> Issue is not reproduced when replacing stat with safe_stat() which
> double checks the file for stale handle.
> 
> On Wed, Dec 4, 2019 at 12:51 PM nikhil jain <address@hidden>
> wrote:
> > A rule which executes in host A creates a .o file.
> > Once it is done, make checks for the next rule which is dependent
> > on this one.
> > 
> > But on the submission host while making the dependency graph again,
> > it sees that the .o timestamp is not newer which means it is still
> > reading the old .o file.
> > 
> > So it doesn't build the target. 
> > I know this is normal as it is on NFS so latency is there.

Can it work if you just delete the .o file before you invoke the
command to recreate it?  Then it will either not exist, or it will
exist and have the right timestamp.

> > But can I do something from make side to cover this latency? I
> > tried putting sleep. It works but we don't know what is the optimal
> > sleep value.
> > 
> > Also, sleep slows down the complete build time.
> > 
> > I see a function safe_stat() and now it is convert d to just stat()
> > 
> > What was the difference actually ? Why we moved from safe_stat() to
> > stat?

That change happened long before GNU make 3.81 was released.  In fact,
it was made by Roland before I even started maintaining GNU make; from
the ChangeLog:

Mon Dec 11 22:26:15 1995  Roland McGrath  <address@hidden>
  ...
        * misc.c (safe_stat): Function removed.
        * read.c, commands.c, remake.c, vpath.c: Use plain stat instead of
        safe_stat.

There is no information in the ChangeLog or commit message as to why
this was done.

This change would have been included in every GNU make starting with
version 3.75 which was released in August 1996.

However, looking back into the history I can see that all that the
safe_stat() function did was loop if we received an EINTR error.  The
current code already does this; stat() calls are embedded in the
EINTRLOOP macro which does the same thing.

I also can't see how looping on EINTR would help your problem, because
you only get EINTR if the stat() was interrupted by a signal and that
wouldn't help your setup.

Perhaps if you explained (a) what your replacement safe_stat() function
did, (b) where you found the safe_stat you're using, and (c) what
changes you made to GNU make code to call safe_state, some of the
mystery could be removed.