Re: using new versions of emacs without stoping a session

[Eli Zaretskii]

> From: YUE Daian <sheepduke@gmail.com>
> Date: Thu, 18 Apr 2019 10:47:01 +0800
> 
> > With one caveat: Windows won't let you overwrite a running executable,
> > so the link step of compiling Emacs will fail on Windows until you
> > shut down your running session.
> 
> Just out of curiosity: Why does Windows do so?
> 
> I mean, compilation process should have no effect on running processes.

Most (all?) modern systems use the executable files as backing store,
loading code and data from them lazily, as needed.  So they all cannot
allow the data of the executable file to be removed or replaced by
something different.  So your "should have no effect" assertion is
inaccurate.

The difference between the systems is on the filesystem level: by
default Windows doesn't allow to unlink file's data from its directory
entry, if some application has that file open, while most Unix
filesystems by default do allow that.  I don't know why Windows'
default is what it is.  Some say that such a default leads to a safer
system: at any given moment all the programs that run use the same
version of a certain library and the same executable code.  But I'm
not convinced that this is the real reason.