Re: [RFC] pre-c89 in libltdl

[Gary V. Vaughan]

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Bob Friesenhahn wrote:
| On 20 Apr 2004, Alexandre Oliva wrote:
|
|>>As I am on a libltdl code simplification fix, a patch to drop MUTEX
|>>fluff
|>>entirely will be on its way shortly...
|>
|>Leaving mutexes up to the caller means that an app that links with
|>multiple libraries that each wants to ltdlopen other stuff, odds are
|>that the libs are all going to have to be modified to use a single
|>mutex.  Remember that if each caller uses its own mutex, each one
|
|
| This is a good point.

Except that I am pretty sure libltdl will choke if you link 2 libraries
that each use it :-(

On the other hand, my next refactoring patch will use preloading through
the libltdl apis to load the other loaders -- to make that work (so that
another caller can use libltdl concurrently) I'll have to fix that problem
if I trip over it.

| The problem with the libltdl thread-safety-support APIs as they exist
| today is that they require a higher-level locking mechanism than a
| simple POSIX mutex since they require that the user-provided lock be
| re-entrant when invoked by the locking thread.  POSIX mutexes are not
| re-entrant by the same thread.
|
| It is wise to protect dl* calls since any POSIX specification for
| these APIs is relatively new and the extra protection should not cause
| any harm.

If a thread-safe library is using libltdl, then I'd be interested to see
how it does it, because as Bob says, we don't have POSIX compliant locking.
I suspect that such libraries already POSIX mutex lock around our APIs
anyhow, and 2 such libraries will each have their own mutex -- so we have
the same problem.  Plus a bunch of unused (untested!) mutex fluff in our
code.

I'm still for removing the current mutex implementation, with an eye to
putting a POSIX compatible implementation back in when I've pulled apart
the ugly bits in ltdl.c to remove the reentrant lock requirement.

Cheers,
        Gary.
- --
Gary V. Vaughan      ())_.  address@hidden,gnu.org}
Research Scientist   ( '/   http://tkd.kicks-ass.net
GNU Hacker           / )=   http://www.gnu.org/software/libtool
Technical Author   `(_~)_   http://sources.redhat.com/autobook
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