Re: [Valgrind-developers] More updates

[Jeremy F. <je...@go...>]

On Mon, 2002-10-21 at 21:45, Julian Seward wrote:
    Nick: I spotted the infamous (?) VG_(get_current_tid_1_if_root)
    and specifically this:
    
       if (0 == vg_tid_currently_in_baseBlock)
          return 1;     /* root thread */
    
    What's the meaning of the 0 here?  Where is it set?  AFAICS the only
    valid values of vg_tid_currently_in_baseBlock are either 1 .. VG_N_THREADS
    or VG_INVALID_THREADID, so I guess I'm missing something here?

No, I don't think so.  I don't think that function means anything at
all.  I was very close to removing it altogether.
    
    I don't feel like I'm seeing a consistent story I'm happy with re
    vg_tid_currently_in_baseBlock -- can you two clarify?

I put the stronger assert into save_thread_state() because I couldn't
see any good reason why the tid argument should ever mismatch the value
of vg_tid_currently_in_baseBlock.  The assertion failed on the first
thread create, but I think my fix makes sense.  Thread creation copies
the parent thread's context into the child via the baseBlock.  In a
sense the ownership of the baseBlock changes during the copy, which is
what the assignment to vg_tid_currently_in_baseBlock indicates:

    VG_(load_thread_state)(parent_tid);		/* load parent thread state into baseBlock */
+   vg_tid_currently_in_baseBlock = tid;	/* give ownership of baseBlock to child */
    VG_(save_thread_state)(tid);		/* save new state into new thread */

    
    It seems like, with that change, it will be impossible to
    know from the value of vg_tid_currently_in_baseBlock whether or 
    not baseBlock is "full".

No, because save_thread_state() assigns vg_tid_currently_in_baseBlock
withVG_INVALID_THREADID, so you know the baseBlock contains nothing
afterwards.  It gets reassigned with a valid tid on load_thread_state().

    J