Re: lib/54661: pthread_self() returns invalid value in some circumstances

[Tom Lane <tgl%sss.pgh.pa.us@localhost>]

The following reply was made to PR lib/54661; it has been noted by GNATS.

From: Tom Lane <tgl%sss.pgh.pa.us@localhost>
To: gnats-bugs%netbsd.org@localhost, Joerg Sonnenberger <joerg%bec.de@localhost>
Cc: lib-bug-people%netbsd.org@localhost, netbsd-bugs%netbsd.org@localhost
Subject: Re: lib/54661: pthread_self() returns invalid value in some circumstances
Date: Wed, 30 Oct 2019 10:44:39 -0400

 Joerg Sonnenberger <joerg%bec.de@localhost> writes:
 > The following reply was made to PR lib/54661; it has been noted by GNATS.
 >  On Wed, Oct 30, 2019 at 06:10:00AM +0000, tgl%sss.pgh.pa.us@localhost wrote:
 >>> pthread_self() sometimes returns an invalid pointer ((void *) -1),
 >>> as illustrated in How-To-Repeat.
  
 >  Why do you think it's an invalid pointer? It's an opaque value.
 >  Comparing it against any fixed value is a bug in the caller.
 
 I tend to agree that Python shouldn't be checking for -1, but even
 if it removed that check, this behavior would still be problematic,
 because pthread_self() is returning a value that won't work correctly
 in later thread operations.  For example, it will not compare equal
 to the result of a later pthread_self() if somebody successfully
 loads/initializes libpthread.so in between.
 
 I've now looked at the relevant libpthread code, and what seems to be
 happening is this: libpython.so is invoking libpthread's version of
 pthread_self(), but that is just redirecting to the stub version in
 libc, evidently because pthread__init hasn't been called.  So the
 question is why not.  I see bug fixes in libpthread's CVS history
 that claim to be fixing cases where libpthread is dlopen'd, but
 somehow that's not working here.  Maybe the case where libpthread
 is a dependency of a dlopen'd library isn't covered?
 
 I also kind of wonder why the redirect-to-the-stubs behavior is
 there at all.  Why not just forcibly do pthread__init, if it's not
 been done already, when one of libpthread's functions is called?
 
 			regards, tom lane