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Don't invoke `on_thread_exit ()' from a pthread key destructor.

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The `on_thread_exit ()' function allocates memory via libgc.  When
called from the context of a pthread key detructor, the thread is
essentially "dead" already and `GC_lookup_thread ()' returns NULL,
which triggers an assertion in libgc's `thread_local_alloc.c'.  This
patch arranges so that `on_thread_exit ()' is called from a suitable
context.

* libguile/threads.c (on_thread_exit): Remove now invalid comment
  about access to libgc's TLS.
  (init_thread_key): Don't pass `on_thread_exit ()' to
  `scm_i_pthread_key_create ()'.
  (scm_leave_guile_cleanup): Invoke `do_thread_exit ()'.
  (really_launch): Invoke `pthread_exit ()'.
This commit is contained in:
Ludovic Courtès 2008-10-31 00:27:20 +01:00
parent 979172b656
commit 47b6e9bd8e
1 changed files with 9 additions and 17 deletions
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26
libguile/threads.c
View file

@ -573,22 +573,10 @@ on_thread_exit (void *v)
/* Unblocking the joining threads needs to happen in guile mode
since the queue is a SCM data structure. */
/* Note: `scm_with_guile ()' invokes `GC_local_malloc ()', which accesses
thread-local storage (TLS). If said storage is accessed using
`pthread_getspecific ()', then it may be inaccessible at this point,
having been destroyed earlier, since the invocation order of destructors
associated with pthread keys is unspecified:
http://www.opengroup.org/onlinepubs/009695399/functions/pthread_key_create.html
Thus, `libgc' *must* be compiled with `USE_COMPILER_TLS' for this code
to work.
FIXME: Worse, we can't use the GC at all at this point. With assertions
enabled, `libgc' triggers an assertion in `thread_local_alloc.c' upon
the next `cons' showing that `GC_lookup_thread ()' returned NULL; this
is due to the fact that we're in the thread destructor. */
scm_with_guile (do_thread_exit, v);
/* Note: Since `do_thread_exit ()' uses allocates memory via `libgc', we
assume the GC is usable at this point, and notably that thread-local
storage (TLS) hasn't been deallocated yet. */
do_thread_exit (v);
/* Removing ourself from the list of all threads needs to happen in
non-guile mode since all SCM values on our stack become
@ -619,7 +607,7 @@ static scm_i_pthread_once_t init_thread_key_once = SCM_I_PTHREAD_ONCE_INIT;
static void
init_thread_key (void)
{
scm_i_pthread_key_create (&scm_i_thread_key, on_thread_exit);
scm_i_pthread_key_create (&scm_i_thread_key, NULL);
}
/* Perform any initializations necessary to bring the current thread
@ -782,6 +770,7 @@ SCM_UNUSED static void
scm_leave_guile_cleanup (void *x)
{
scm_leave_guile ();
on_thread_exit (SCM_I_CURRENT_THREAD);
}
void *
@ -890,6 +879,9 @@ really_launch (void *d)
else
t->result = scm_catch (SCM_BOOL_T, thunk, handler);
/* Trigger a call to `on_thread_exit ()'. */
pthread_exit (NULL);
return 0;
}