crerating coredump of multithreaded process

[Norbert Koch]

Hello.

When trying to create the coredump of a running
process (without killing it) under FreeBSD 10.3
I am seeing a somewhat strange behaviour.

As I want to see the state of all threads, the q&d way
of fork() + SIGABRT does not work for me.

So, what I do is having a supervisor program waiting for SIGUSR1.
When my application signals the wish to be coredumped
it sends SIGSTOP to itself immediately after sending SIGUSR1.
The supervisor then forks gcore.

 From what I can see using top, my application immediately starts
again as if SIGCONT has been received while gcore hangs in wait.

Gcore calls ptrace(PT_ATTACH) followed by waitpid().
So I assume that the ptrace call restarts my application
and waitpid hangs (why?).

If I manually send SIGCONT to my stopped application
immediately before exec-ing gcore, the coredump is being
created, but for obvious reasons  not as consistent as
I want it to be.

I should add that in my application most other signals are
blocked. Blocking (or not) SIGCONT seems to have no effect.

Am I doing something wrong here? If yes, ist there
a different/better/more elegant way of creating a consistent coredump?

Thank you.

-- 
Dipl.-Ing. Norbert Koch
Entwicklung Prozessregler



*****************************************
* demig Prozessautomatisierung GmbH     *
*                                       *
* Anschrift:          Haardtstrasse 40  *
*                       D-57076 Siegen  *
* Registergericht:     Siegen HRB 2819  *
* Geschaeftsfuehrer:   Joachim Herbst,  *
*                        Winfried Held  *
* Telefon:              +49 271 772020  *
* Telefax:              +49 271 74704   *
* E-Mail:                info at demig.de  *
*                  http://www.demig.de  *
*****************************************