Re: SIGCONT misbehaviour in Linux
Simon Patience (sp@albion.engr.sgi.com)
Fri, 10 Dec 1999 15:37:51 -0800 (PST)
Brian Pomerantz wrote:
|> On Fri, Dec 10, 1999 at 07:29:25AM -0800, Simon Patience wrote:
|> > In article <82mvls$aqtrr@fido.engr.sgi.com>, you write:
|> > |> On 8 Dec 1999, Ulrich Drepper wrote:
|> > |> >This is not what happens on other platforms. At least with my limited
|> > |> >testing I found that if you do on Solaris
|> > |> >
|> > |> > sleep 10
|> > |> > ^Z
|> > |> > fg
|> > |> >
|> > |> >the process will continue to sleep.
|> > |>
|> > |> That's not enough to tell what the kernel is doing, maybe they have a bit
|> > |> smarter sleep(1) program. `sleep` can be changed to run nanosleep again if
|> > |> it received -EINTR and `req` is not null. You only have to pass as `req`
|> > |> the `rem` that you got back from the previous nanosleep call.
|> >
|> > No, the problem is that you shouldn't have interrupted it in the first
|> > place. What is the point of interrupting a blocked process so that you
|> > can block it?
|>
|> Isn't a process in a blocked state when it is waiting on I/O? I often
|> will hit ^Z for a long tarball extraction and run it in the
|> background. When I hit ^Z, the process could be waiting for I/O when
|> the signal comes through, thus a time when I want to interrupt a
|> blocked process to block it.
My point was that you could just leave it blocked waiting for the I/O.
If you type fg before the I/O completes then the process will just
execute and return as if nothing had happened when the I/O finally
completes. If the I/O completes first then the processes winds its way
back to the return from the system call, notices that it is stopped and
blocks itself there. When the SIGCONT arrives, the process unblocks and
returns from the system call normally.
This is far better (less code, less complexity) than unblocking the I/O
(which may have partial results) getting the process to block somewhere
else and then trying to work out what on earth the right thing to do is
when SIGCONT arrives.
Simon.
--
Simon Patience Phone: (650) 933-4644
Silicon Graphics, Inc FAX: (650) 962-8404
1600 Amphitheatre Pkwy Email: sp@sgi.com
Mountain View, CA 94043-1389
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