Using mutex.owner to detect re-entry

[Tom Schouten <tom@xxxxxxxxx>]

Hi List,

Is it safe to use the following approach to use a mutex to detect re-entry?
( i.e. to avoid thread-local variables to keep an entry counter.)


static int re_entry(cyg_mutext_t *m) {
    return (m->owner == (void*)cyg_thread_self());
}

As used in the following fragment:

cyg_mutex_t m;

int some_call() {
  if (re_entry(&m)) {
    /* Break off recursion. */
    return error_re_entry;
  }
  else {
    cyg_mutex_lock(&m);
    int err = re_entry_protected_call();   /* Might call some_call(), 
which should then return error_re_entry */
    cyg_mutex_unlock(&);
    return err;
  }
}

Rationale: This is safe because (see mutex.cpp)

- If it's not self it's either NULL or the value of another thread, but 
if this is the case it can never become self due to a race condition.
I.e. we're sure this is not a re-entrant call

- It's self if and only if it's a re-entrant call.


Cheers,
Tom


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