Pthreads and GDB?

Jan Chludzinski
Tue Jul 12 17:02:00 GMT 2011

> Since cygwin1.dll is multithreaded, I routinely set breakpoints which
> are only hit in a thread.  So, yes, gdb is supposed to be multi-thread
> aware.

I have a 2 thread program.  I set the break for main() and run (to main):

      (gdb) b main
      Breakpoint 1 at 0x401191
      (gdb) r
      Starting program: /home/John/projects/pthreads/test1/a.exe
      [New thread 3680.0x13e8]
      Error: dll starting at 0x76ff0000 not found.
      Error: dll starting at 0x76590000 not found.
      Error: dll starting at 0x76ff0000 not found.
      Error: dll starting at 0x76c40000 not found.
      [New thread 3680.0xc7c]
      Breakpoint 1, 0x00401191 in main ()

Wait a few seconds and start to step:

      (gdb) n
      Single stepping until exit from function main,
      which has no line number information.
      [New thread 3680.0x1410]
      [New thread 3680.0x1540]
      Counter value functionCount1: 1
      Counter value functionCount2: 2
      Final count: 10
      Program exited normally.

As you can see the threads have finished executing, along with the
main thread, *before * I ever get a chance to step to the first
pthread_create().  Let alone set a break in a thread.


Thanks, Jan

On Tue, Jul 12, 2011 at 6:16 AM, Jan Chludzinski
<> wrote:
> I went to to read about GDB and threads since I'm having
> trouble working with ptheads under GDB on Cygwin.  I notice this on
> the web site:
> "Warning: These facilities are not yet available on every GDB
> configuration where the operating system supports threads. If your GDB
> does not support threads, these commands have no effect. For example,
> a system without thread support shows no output from `info threads',
> and always rejects the thread command, like this:"
> What the level of support for threads with GDB under Cygwin?
> Switching between threads causes seg-faults.  Also, I thought that
> while you're stepping through one thread, the other threads weren't
> running? Shouldn't I be able to set a breakpoint in a thread before
> pthread_create() is invoked?  Doesn't appear to be the case?
> ---Jan

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