Resuming a single suspended thread on Linux

Resuming a single suspended thread on Linux

[Yaki Tebeka]

Hi All

I am implementing a special purpose debugger using gdb.
When a program is being debugged, I load into it a special library
that runs a thread (inside the debugged process) that reports data to
the debugger using a socket communication.

This approach works well on Windows (with another debugger engine),
but when I try to implement it using gdb on Linux, I realize that
whenever the debugged application execution is suspended (breakpoint /
etc), my data reporting thread, that runs inside the debugged process,
is also suspended.

I tried "thread apply X continue", but it seems to continue the entire
process (which, as far as I understand, is the right behavior on
Linux).

Does anyone have an idea for a solution to my problem.

Thanks

 Yaki Tebeka

Re: Resuming a single suspended thread on Linux

[Jim Blandy]

"Yaki Tebeka" <tebeka@gmail.com> writes:
> I am implementing a special purpose debugger using gdb.
> When a program is being debugged, I load into it a special library
> that runs a thread (inside the debugged process) that reports data to
> the debugger using a socket communication.
>
> This approach works well on Windows (with another debugger engine),
> but when I try to implement it using gdb on Linux, I realize that
> whenever the debugged application execution is suspended (breakpoint /
> etc), my data reporting thread, that runs inside the debugged process,
> is also suspended.
>
> I tried "thread apply X continue", but it seems to continue the entire
> process (which, as far as I understand, is the right behavior on
> Linux).
>
> Does anyone have an idea for a solution to my problem.

Hi --- have you looked at the documentation for 'set
scheduler-locking'?  That might work for you.

Re: Resuming a single suspended thread on Linux

[Yaki Tebeka]

Hi Jim

Thanks for the suggested solution.

I read the "set scheduler-locking" feature documentation few times
(http://sourceware.org/gdb/current/onlinedocs/gdb_6.html#IDX281) and I
must admit that I am not quite sure that I understand it correctly...

One of it sentences says that the other threads are "completely free
to run when you use commands like `continue', `until', or `finish'".
If I understand this correctly, it will not help in my case.

Please let me know if I didn't understand this mechanism correctly.

Yaki


On 1/7/07, Jim Blandy <jimb@codesourcery.com> wrote:
>
> "Yaki Tebeka" <tebeka@gmail.com> writes:
> > I am implementing a special purpose debugger using gdb.
> > When a program is being debugged, I load into it a special library
> > that runs a thread (inside the debugged process) that reports data to
> > the debugger using a socket communication.
> >
> > This approach works well on Windows (with another debugger engine),
> > but when I try to implement it using gdb on Linux, I realize that
> > whenever the debugged application execution is suspended (breakpoint /
> > etc), my data reporting thread, that runs inside the debugged process,
> > is also suspended.
> >
> > I tried "thread apply X continue", but it seems to continue the entire
> > process (which, as far as I understand, is the right behavior on
> > Linux).
> >
> > Does anyone have an idea for a solution to my problem.
>
> Hi --- have you looked at the documentation for 'set
> scheduler-locking'?  That might work for you.
>


-- 
Yaki Tebeka

Re: Resuming a single suspended thread on Linux

[Daniel Jacobowitz]

On Sun, Jan 07, 2007 at 07:00:26PM +0200, Yaki Tebeka wrote:
> Hi Jim
> 
> Thanks for the suggested solution.
> 
> I read the "set scheduler-locking" feature documentation few times
> (http://sourceware.org/gdb/current/onlinedocs/gdb_6.html#IDX281) and I
> must admit that I am not quite sure that I understand it correctly...
> 
> One of it sentences says that the other threads are "completely free
> to run when you use commands like `continue', `until', or `finish'".
> If I understand this correctly, it will not help in my case.
> 
> Please let me know if I didn't understand this mechanism correctly.

That sentence only describes the behavior when you set it to "step".
If you set it to "on", you can run just a single thread.


-- 
Daniel Jacobowitz
CodeSourcery

Re: Resuming a single suspended thread on Linux

[Yaki Tebeka]

Hi Daniel and Jim

I tried the suggested solution, but unfortunately, it does not seem to work.
I am running Fedora Core 5, 64 bit on an AMD processor.
After I call "set scheduler-locking on", and "continue", the entire
debugged process seem to remain freeze.
I tried setting my data collection thread as the active thread and
even setting the main thread as the active thread, but both options
does not seem to work.

Do you know if its a GDB bug, or an "expected behaviour" on Linux?

Can you suggest another solution to my problem?

Thanks

  Yaki



On 1/8/07, Daniel Jacobowitz <drow@false.org> wrote:
> On Sun, Jan 07, 2007 at 07:00:26PM +0200, Yaki Tebeka wrote:
> > Hi Jim
> >
> > Thanks for the suggested solution.
> >
> > I read the "set scheduler-locking" feature documentation few times
> > (http://sourceware.org/gdb/current/onlinedocs/gdb_6.html#IDX281) and I
> > must admit that I am not quite sure that I understand it correctly...
> >
> > One of it sentences says that the other threads are "completely free
> > to run when you use commands like `continue', `until', or `finish'".
> > If I understand this correctly, it will not help in my case.
> >
> > Please let me know if I didn't understand this mechanism correctly.
>
> That sentence only describes the behavior when you set it to "step".
> If you set it to "on", you can run just a single thread.
>
>
> --
> Daniel Jacobowitz
> CodeSourcery
>


-- 
Yaki Tebeka

Re: Resuming a single suspended thread on Linux

[Daniel Jacobowitz]

On Mon, Jan 15, 2007 at 11:47:37AM +0200, Yaki Tebeka wrote:
> Hi Daniel and Jim
> 
> I tried the suggested solution, but unfortunately, it does not seem to work.
> I am running Fedora Core 5, 64 bit on an AMD processor.
> After I call "set scheduler-locking on", and "continue", the entire
> debugged process seem to remain freeze.
> I tried setting my data collection thread as the active thread and
> even setting the main thread as the active thread, but both options
> does not seem to work.
> 
> Do you know if its a GDB bug, or an "expected behaviour" on Linux?

Well, it is not what I would personally have expected.  I'm afraid I
don't know what might have happened.

-- 
Daniel Jacobowitz
CodeSourcery

Re: Resuming a single suspended thread on Linux

[Jim Blandy]

"Yaki Tebeka" <tebeka@gmail.com> writes:
> I tried the suggested solution, but unfortunately, it does not seem to work.
> I am running Fedora Core 5, 64 bit on an AMD processor.
> After I call "set scheduler-locking on", and "continue", the entire
> debugged process seem to remain freeze.
> I tried setting my data collection thread as the active thread and
> even setting the main thread as the active thread, but both options
> does not seem to work.
>
> Do you know if its a GDB bug, or an "expected behaviour" on Linux?
>
> Can you suggest another solution to my problem?

Without knowing more, I couldn't say.

Does the thread you're running wait on any mutexes that might be held
by the stopped threads?