Re: [PATCH] GDB checkpoint can't/shouldn't be possible with multiple threads on Linux

Pedro Alves
2011-04-12T12:55:20Z

On Tuesday 12 April 2011 12:55:05, Kevin Pouget wrote:
> > Next time please post ChangeLog entries as plaintext,
> > separate from the patch.
>
> 2011-04-12 Kevin Pouget <kevin.pouget@st.com>
>
> PR threads/12628
>
> * linux-fork.c (checkpoint_command): Disallow checkpointing of
> processes with multiple threads.
> (inf_has_multiple_thread_cb): New function.
>
> > > diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
> > > index 7f654af..c137604 100644
> > > --- a/gdb/linux-fork.c
> > > +++ b/gdb/linux-fork.c
> > > @@ -628,6 +628,11 @@ checkpoint_command (char *args, int from_tty)
> > > pid_t retpid;
> > > struct cleanup *old_chain;
> > >
> > > + /* Ensure that the inferior is not multithreaded. */
> >
> > Double space after periods.
>
> fixed
>
> > > + update_thread_list () ;
> > > + if (thread_count () > 1)
> > > + error (_("checkpoint: can't checkpoint multiple threads.")) ;
> >
> > You have spurious spaces before `;'.
>
> fixed
>
> > thread_count() returns the sum total number of threads of all
> > inferiors/process. You want the number of threads of the
> > current process only. AFAIR, there's no function handy that
> > returns you that. (Since you're interested in checking for multiple
> > threads, you could use iterate_over_threads with a
> > callback that returns true if it sees a second thread for a
> > given process, so you don't really need to count all
> > the threads.)
>
> you're right, I updated the patch as suggested

Can you have a dialogue with your mailer, convincing it
to attach text files as Content-Type: text/$SOMETHING
rather than application/octet-stream + base64 ?
It's more steps to to read and harder to quote-for-review
binary attachments than should be necessary. Thanks.

diff --git a/gdb/linux-fork.c b/gdb/linux-fork.c
index 7f654af..8a18d42 100644
--- a/gdb/linux-fork.c
+++ b/gdb/linux-fork.c
@@ -616,6 +616,20 @@ linux_fork_checkpointing_p (int pid)
return (checkpointing_pid == pid);
}

> +static int
> +inf_has_multiple_thread_cb (struct thread_info *tp, void *data)

Misses a short describing comment. Something like

/* Callback for iterate over threads. Used to check whether
the current inferior is multi-threaded. Returns true as soon
as it sees the second thread of the current inferior. */

> +{
> + int *has_multiple_threads = (int *) data;
> +
> + gdb_assert(current_inferior() != NULL);

(Many other things would break if this wasn't true.)
Missing spaces before `('.

> + if (current_inferior()->pid == GET_PID(tp->ptid))

Missing spaces before `('. Please use ptid_get_pid.

if (current_inferior ()->pid == ptid_get_pid (tp->ptid))

> + (*has_multiple_threads)++;
> +
> + /* Stop the iteration if multiple threads have been detected. */
> + return *has_multiple_threads > 1;
> +}
> +
> static void
> checkpoint_command (char *args, int from_tty)
> {
> @@ -627,7 +641,16 @@ checkpoint_command (char *args, int from_tty)
> struct fork_info *fp;
> pid_t retpid;
> struct cleanup *old_chain;
> + int has_multiple_threads = 0 ;

Space before `;' again. Let's reserve variables named
`has_FOO' for booleans. Otherwise, the code is harder
to read (the "if (has_multiple_threads > 1)" check below
made me go "hmm?"). You could encapsulate the magic count
in a predicate function:

static int
inf_has_multiple_threads (void)
{
int count = 0;

iterate_over_threads (inf_has_multiple_thread_cb, &count);
return (count > 1);
}

> + iterate_over_threads(inf_has_multiple_thread_cb, &has_multiple_threads);
> + if (has_multiple_threads > 1)
> + error (_("checkpoint: can't checkpoint multiple threads."));

> +
> + if (!target_has_execution) error (_("The program is not being run."));

Each statement goes on its own line.

> + /* Ensure that the inferior is not multithreaded. */
> + update_thread_list () ;

Space before `;' again.

> + iterate_over_threads(inf_has_multiple_thread_cb, &has_multiple_threads);
> + if (has_multiple_threads > 1)
> + error (_("checkpoint: can't checkpoint multiple threads."));
> +

Missing spaces again.

--
Pedro Alves