pthread_cancel and EH: let's try this again

[Alexander Terekhov]

Peter Dimov wrote:
[...]
> Before that, an implementation that used a separate "cleanup mode" flag
> (which has the advantage of not interfering with the client's cancelstate
> calls) was conforming. 

Nope. Because

http://www.opengroup.org/onlinepubs/009695399/functions/xsh_chap02_09.html#tag_02_09_05_01

says nothing about "separate cleanup mode flag" and hence per XSH 2.9.5,

http://opengroup.org/austin/mailarchives/austin-review-l/msg01450.html

can be written as 

     ....
     int state;
     pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &state);
     if (PTHREAD_CANCEL_ENABLE == state) {
       pthread_setcancelstate(state, &state);
       pthread_cancel(pthread_self());
       pthread_testcancel();
       errno = ECANCELED;
       perror("NON-CONFORMING IMPLEMENTATION");
       abort();
     }
     ....

that's apart from

     ....
     int state;
     pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &state);
     if (PTHREAD_CANCEL_ENABLE == state) {
       pthread_setcancelstate(state, &state); // Uh...
       //pthread_cancel(pthread_self());
       //pthread_testcancel();
       pthread_exit(PTHREAD_CANCELED);
     }
     ....

Of course, the "real" fix would be introduction of int 
pthread_expectedcancel() incapsulating 
expected_exception<thread_cancel_request>() query and cancel state check.

     ....
     if (pthread_expectedcancel()) {
       pthread_cancel(pthread_self());
       pthread_testcancel();
       errno = ECANCELED;
       perror("IMPLEMNATION BUG");
       abort();
     }
     ....

     ....
     if (pthread_expectedcancel()) {
       pthread_exit(PTHREAD_CANCELED);
     }
     ....

but without (2-phase) EH machinery, POSIX just can't do that.

regards,
alexander.