[Bug breakpoints/11568] delete thread-specific breakpoint on the thread exit

["cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=11568

--- Comment #4 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
CVSROOT:    /cvs/src
Module name:    src
Changes by:    palves@sourceware.org    2013-09-17 19:32:47

Modified files:
    gdb            : ChangeLog breakpoint.c 
    gdb/testsuite  : ChangeLog 
Added files:
    gdb/testsuite/gdb.threads: thread-specific-bp.c 
                               thread-specific-bp.exp 

Log message:
    PR gdb/11568 - delete thread-specific breakpoints on thread exit

    PR gdb/11568 is about thread-specific breakpoints being left behind
    when the corresponding thread exits.

    Currently:

    (gdb) b start thread 2
    Breakpoint 3 at 0x400614: file thread-specific-bp.c, line 23.
    (gdb) b end
    Breakpoint 4 at 0x40061f: file thread-specific-bp.c, line 29.
    (gdb) c
    Continuing.
    [Thread 0x7ffff7fcb700 (LWP 14925) exited]
    [Switching to Thread 0x7ffff7fcc740 (LWP 14921)]

    Breakpoint 4, end () at thread-specific-bp.c:29
    29      }
    (gdb) info threads
    Id   Target Id         Frame
    * 1    Thread 0x7ffff7fcc740 (LWP 14921) "thread-specific" end () at
thread-specific-bp.c:29
    (gdb) info breakpoints
    Num     Type           Disp Enb Address            What
    2       breakpoint     keep y   0x0000000000400614 in start at
thread-specific-bp.c:23
    breakpoint already hit 1 time
    3       breakpoint     keep y   0x0000000000400614 in start at
thread-specific-bp.c:23 thread 2
    stop only in thread 2
    4       breakpoint     keep y   0x000000000040061f in end at
thread-specific-bp.c:29
    breakpoint already hit 1 time

    Note that the thread-specific breakpoint 3 stayed around, even though
    thread 2 is gone.

    There's no way that breakpoint can trigger again (*), so the PR argues
    that the breakpoint should just be removed, like local watchpoints.
    I'm ambivalent on this -- it could be reasonable to disable the
    breakpoint (kind of like breakpoint in shared library code when the
    DSO is unloaded), so the user could still use it as visual template
    for creating other breakpoints (copy/paste command lists, etc.), or we
    could have a way to change to which thread a breakpoint applies.  But,
    several people pushed this direction, and I don't plan on arguing...

    (*) - actually, there is ...  thread numbers are reset on "run", so
    the user could do "break foo thread 2", "run", and expect the
    breakpoint to hit again on the second thread.  But given gdb's thread
    numbering can't really be stable, that'd only work sufficiently well
    for thread 1, so we'd better call it unsupported.

    So with the patch, whenever a thread is deleted from GDB's list, GDB
    goes through the thread-specific breakpoints and deletes corresponding
    breakpoints.  Since this is user-visible, GDB prints out:

    Thread-specific breakpoint 3 deleted - thread 2 is gone.

    And of course, we end up with:

    (gdb) info breakpoints
    Num     Type           Disp Enb Address            What
    2       breakpoint     keep y   0x0000000000400614 in start at
thread-specific-bp.c:23
    breakpoint already hit 1 time
    4       breakpoint     keep y   0x000000000040061f in end at
thread-specific-bp.c:29
    breakpoint already hit 1 time

    2013-09-17  Muhammad Waqas <mwaqas@codesourcery.com>
    Pedro Alves  <palves@redhat.com>

    PR gdb/11568
    * breakpoint.c (remove_threaded_breakpoints): New function.
    (_initialize_breakpoint): Attach remove_threaded_breakpoints
    as thread_exit observer.

    2013-09-17  Muhammad Waqas  <mwaqas@codesourccery.com>
    Jan Kratochvil  <jan.kartochvil@redhat.com>
    Pedro Alves  <palves@redhat.com>

    PR gdb/11568
    * gdb.thread/thread-specific-bp.c: New file.
    * gdb.thread/thread-specific-bp.exp: New file.

Patches:
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/ChangeLog.diff?cvsroot=src&r1=1.16003&r2=1.16004
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/breakpoint.c.diff?cvsroot=src&r1=1.776&r2=1.777
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/ChangeLog.diff?cvsroot=src&r1=1.3810&r2=1.3811
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.threads/thread-specific-bp.c.diff?cvsroot=src&r1=NONE&r2=1.1
http://sourceware.org/cgi-bin/cvsweb.cgi/src/gdb/testsuite/gdb.threads/thread-specific-bp.exp.diff?cvsroot=src&r1=NONE&r2=1.1

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