Re: LuaLanes on Ubuntu 11.10, kernel 3.0

[Philipp Janda <siffiejoe@...>]

On 10.11.2011 12:04, Benoit Germain wrote:
> 2011/11/10 Philipp Janda<siffiejoe@gmx.net>:
> > A proper solution would probably involve using pthread_cleanup_push to free
> > the Lane's memory on actual cancellation.
>
> I am not sure I get the usage of pthread_cancel_push right. What I
> could do is this:
> Add a pthread_cancel_push()/pthread_cancel_pop() pair at the beginning
> and end of lane_main.

So far so good.

> The callback I provide sets some flag in the s_lane structure.
> In selfdestruct_atexit(), after the call to THREAD_KILL(), I
> block-wait for this flag to be set in the structure, at which point I
> can free it.

That would probably work, but an easier way would be:
static void* lane_main( void* vs ) {
  pthread_cleanup_push( free, vs ); // handles cancels and exits

  // code ...

  pthread_cleanup_pop( TRUE ); // handles reaching end of lane_main
  return 0;
}

That would pop and call 'free( vs )' automatically when/if the thread is 
cancelled or calls pthread_exit. 'pthread_cleanup_pop( TRUE )' pops and 
calls 'free( vs )' manually if the execution reaches the end of lane_main.
You could also replace 'free' with a function that additionally removes 
its argument from the selfdestruct chain. Those functions could also be 
used to release locks if you are cancelled while holding one, etc.

> Would it be ok that way? When the thread actually terminates because
> of the thread_kill() call, am I supposed to call pthread_cancel_pop()
> (which I suppose might not be the case if execution doesn't reach the
> end of lane_main)?

No, pthread_cleanup_(push|pop) only work for the calling thread and the 
pop happens automatically if the thread is cancelled.

Btw. I have some leads about the SIGSEGV in tests/atexit.lua, but I 
don't know how to proceed from here:
[Thread debugging using libthread_db enabled]
Core was generated by `/home/siffiejoe/downloads/lua-5.1.4/src/lua 
tests/atexit.lua'.
Program terminated with signal 11, Segmentation fault.
#0  0x4067bb19 in ?? () from /lib/i386-linux-gnu/libgcc_s.so.1
(gdb) bt
#0  0x4067bb19 in ?? () from /lib/i386-linux-gnu/libgcc_s.so.1
#1  0x4067c078 in ?? () from /lib/i386-linux-gnu/libgcc_s.so.1
#2  0x4067c528 in _Unwind_Resume () from /lib/i386-linux-gnu/libgcc_s.so.1
#3  0x400d53f2 in _Unwind_Resume (exc=0x402fddc0) at 
../sysdeps/gnu/unwind-resume.c:52
#4  0x4011ddeb in _IO_acquire_lock_fct (p=<optimized out>) at libioP.h:985
#5  fputc (c=10, fp=0x40234500) at fputc.c:38
#6  0x0806882b in luaB_print (L=0x40302f80) at lbaselib.c:48
#7  0x08051232 in luaD_precall (L=0x40302f80, func=0x40301990, 
nresults=0) at ldo.c:319
#8  0x0805d7c0 in luaV_execute (L=0x40302f80, nexeccalls=1) at lvm.c:587
#9  0x0805148a in luaD_call (L=0x40302f80, func=0x40301978, nResults=-1) 
at ldo.c:377
#10 0x0804e3ca in f_call (L=0x40302f80, ud=0x402fd33c) at lapi.c:800
#11 0x08050673 in luaD_rawrunprotected (L=0x40302f80, f=0x804e3a0 
<f_call>, ud=0x402fd33c) at ldo.c:116
#12 0x080517f0 in luaD_pcall (L=0x40302f80, func=0x804e3a0 <f_call>, 
u=0x402fd33c, old_top=24, ef=12) at ldo.c:463
#13 0x0804e463 in lua_pcall (L=0x40302f80, nargs=0, nresults=-1, 
errfunc=1) at lapi.c:821
#14 0x40027a11 in ?? ()
#15 0x40302f80 in ?? ()
#16 0x400a7d31 in start_thread (arg=0x402fdb70) at pthread_create.c:304
#17 0x4018e0ce in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:130
Backtrace stopped: Not enough registers or memory available to unwind 
further

The crash happens in one of the print()s. If I comment them out the 
crash goes away. I think one cancelled thread leaves stdio in an invalid 
state.

Philipp