Re: higher-level IO very slow with cygwin1.dll 5.10 (due to set_flags?)

[Mark Thornton <mark dot p dot thornton at ntlworld dot com>]

Pierre A. Humblet wrote:

> On Sat, Jun 26, 2004 at 01:09:40PM -0400, Christopher Faylor wrote:
>  
>
> > On Sat, Jun 26, 2004 at 12:05:54PM -0400, Pierre A. Humblet wrote:
> >    
> >
> > > Beware, I found this:
> > > 2000-05-19  DJ Delorie  <dj@cygnus.com>
> > > 	* libc/include/stdio.h: no getc/putc macros for cygwin; causes
> > > 	compatibility issues with different dll versions
> > > so you may need to recompile when updating cygwin.
> > >      
> > Also wouldn't that work around the file locks that were ostensibly put
> > there for a reason?
> >    
>
> That crossed my mind. But there is no file lock in the macro, which is
> used by systems other than cygwin. How do they manage it?
> I also assume that single threaded programs don't need the lock.
>  
Is the lock to ensure that normal POSIX append semantics are obtained 
when two processes are writing to the same file? Normal win32 behaviour 
would tend to overwrite whatever had been written by the other process 
unless the file is only opened once and then the handle duplicated (very 
messy). So if you want append mode to work correctly (i.e. Unix style), 
then you always have to use file locks around any file write operation 
that is expected to be atomic. The locks could be avoided for non append 
mode writes and where the file has been exclusively locked anyway.

Single thread programs will need the lock just as much as multithread. 
You can only avoid it if you just a single process (with just one thread),.

Mark Thornton


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