PTHREAD_INVARIANTS in 5.x

[Jonathan Noack]

On 05/11/05 21:53, Daniel Eischen wrote:
> On Wed, 11 May 2005, Jonathan Noack wrote:
>>I checked out _PTHREADS_INVARIANTS for libthr and libpthread on CURRENT.
>>  As far as I can tell, all but one of the defines under
>>_PTHREADS_INVARIANTS are ASSERTs; they check for a condition and if it
>>is false result in a fatal error.  These should be very visible if they
>>are being tripped.  Only MUTEX_INIT_LINK actually *does* something.  It
>>is defined in src/lib/libpthread/thread/thr_mutex.c at lines 43-46 and
>>in src/lib/libthr/thread/thr_mutex.c at lines 44-47:
>>
>>#define MUTEX_INIT_LINK(m)              do {            \
>>         (m)->m_qe.tqe_prev = NULL;                      \
>>         (m)->m_qe.tqe_next = NULL;                      \
>>} while (0)
>>
>>I'm not sure what impact removing this explicit initialization would
>>have.  If we're not seeing fatal errors, everything else is just slowing
>>us down.  Assuming we feel our thread implementations are production
>>worthy, we should disable these checks for releases.  That is, unless I
>>am missing something...
> 
> I wrote the darn things, and they are useful in that they can
> provide useful information if there are bugs and also for
> detecting if the application is linked to multiple thread
> libraries.  For the init links macro, it is only used when
> the mutex is initialized and on unlock.  It's two instructions.
> The others are also just a couple of instructions and shouldn't
> be called often.
> 
> This is way overblown and they're other areas for much
> better optimizations than worrying about a couple of
> instructions.  Perhaps if it were called _PTHREAD_ROBUST
> instead of _PTHREAD_INVARIANTS, noone would notice ;-)

So I *was* missing something: the Big Picture.  Detecting if an 
application is linked to multiple thread libraries is definitely a keeper.

When I see your name in an email, the hash that is my brain returns 
"threads guy".  Your previous responses to this topic (which my brain 
referenced as authoritative) seemed to indicate that you weren't sure 
and further investigation was necessary, so I looked into it.  Sorry if 
I misunderstood that.

> That's the last I'll say.  re@ can do whatever they want
> with my blessing.

Fair enough.

-- 
Jonathan Noack | noackjr at alumni.rice.edu | OpenPGP: 0x991D8195
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