[lttng-dev] [RFC] Userspace RCU library internal error handling

[Mathieu Desnoyers]

Hi,

Currently, liburcu calls "exit(-1)" upon internal consistency error.
This is not pretty, and usually frowned upon in libraries.

One example of failure path where we use this is if pthread_mutex_lock()
would happen to fail within synchronize_rcu(). Clearly, this should
_never_ happen: it would typically be triggered only by memory
corruption (or other terrible things like that). That being said, we
clearly don't want to make "synchronize_rcu()" return errors like that
to the application, because it would complexify the application error
handling needlessly.

So instead of calling exit(-1), one possibility would be to do something
like this:

#include <signal.h>
#include <pthread.h>
#include <stdio.h>

#define urcu_die(fmt, ...)                      \
        do {    \
                fprintf(stderr, fmt, ##__VA_ARGS__);    \
                (void) pthread_kill(pthread_self(), SIGBUS);    \
        } while (0)

and call urcu_die(); in those "unrecoverable error" cases, instead of
calling exit(-1). Therefore, if an application chooses to trap those
signals, it can, which is otherwise not possible with a direct call to
exit().

Thoughts ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com