Re: [RFC] EINTR and PC loser-ing library design

[Rich Felker <dalias@libc.org>]

On Mon, Dec 08, 2014 at 10:00:31AM -0500, Rich Felker wrote:
> On Mon, Dec 08, 2014 at 03:45:33PM +0100, Laurent Bercot wrote:
> > On 08/12/2014 15:32, Rich Felker wrote:
> > 
> > >The system call restarts (or, formally, it's as if it were never
> > >interrupted; EINTR only applies to signal _handlers_).
> > 
> >  Could you please provide a pointer to the specification that
> > guarantees this ? I've never been able to find a normative text that
> > ensures you will never get EINTR unless you explicitly install a
> > signal handler without SA_RESTART.
> 
> I've had a hard time pinning it down too, but that's what all modern
> (e.g. modern enough to have a working sigaction) implementations do,
> and it's the obviously correct behavior. I would consider making a
> request for clarification here, but after what happened with the C
> locale issue, I'd kinda fear some trolls would appear and insist that
> EINTR be allowed to happen for no good reason. :(

The closest I can find is XSH 2.4.4 Signal Effects on Other Functions:

    Signals affect the behavior of certain functions defined by this
    volume of POSIX.1-2008 if delivered to a process while it is
    executing such a function. If the action of the signal is to
    terminate the process, the process shall be terminated and the
    function shall not return. If the action of the signal is to stop
    the process, the process shall stop until continued or terminated.
    Generation of a SIGCONT signal for the process shall cause the
    process to be continued, and the original function shall continue
    at the point the process was stopped. If the action of the signal
    is to invoke a signal-catching function, the signal-catching
    function shall be invoked; in this case the original function is
    said to be "interrupted" by the signal. If the signal-catching
    function executes a return statement, the behavior of the
    interrupted function shall be as described individually for that
    function, except as noted for unsafe functions. Signals that are
    ignored shall not affect the behavior of any function; signals
    that are blocked shall not affect the behavior of any function
    until they are unblocked and then delivered, except as specified
    for the sigpending() and sigwait() functions.

The above text seems to be what defines the concept of "interrupted",
and it's in terms of a "signal-catching function". The behavior "as
described individually for that function" is usually to fail with
EINTR, but it's overridden by the text of the sigaction function which
defines SA_RESTART to automatically restart functions interrupted in
this sense.

Rich