Date: Sat, 30 Aug 2008 12:15:31 -0400 (EDT) From: Daniel Eischen <deischen@freebsd.org> To: Kostik Belousov <kostikbel@gmail.com> Cc: davidxu@freebsd.org, Andriy Gapon <avg@icyb.net.ua>, freebsd-threads@freebsd.org Subject: Re: mysterious hang in pthread_create Message-ID: <Pine.GSO.4.64.0808301200460.9898@sea.ntplx.net> In-Reply-To: <20080830155622.GF2038@deviant.kiev.zoral.com.ua> References: <48B70A98.5060501@icyb.net.ua> <48B7101E.7060203@icyb.net.ua> <48B71BA6.5040504@icyb.net.ua> <20080829141043.GX2038@deviant.kiev.zoral.com.ua> <48B8052A.6070908@icyb.net.ua> <20080829143645.GY2038@deviant.kiev.zoral.com.ua> <Pine.GSO.4.64.0808291223240.5086@sea.ntplx.net> <20080829190506.GA2038@deviant.kiev.zoral.com.ua> <Pine.GSO.4.64.0808301128410.9898@sea.ntplx.net> <20080830155622.GF2038@deviant.kiev.zoral.com.ua>
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On Sat, 30 Aug 2008, Kostik Belousov wrote: > On Sat, Aug 30, 2008 at 11:32:35AM -0400, Daniel Eischen wrote: >> On Fri, 29 Aug 2008, Kostik Belousov wrote: >>> >>> As demonstrated by Andriy' example, we need _thr_rtld_init() be called >>> before any rtld locks are given chance to be acquired. _thr_rtld_init() >>> shall be protected from repeated invocation, and _thr_setthreaded() >>> implements exactly this. >>> >>> If calling _thr_setthreaded(1) has not quite right intent, could you, >>> please, suggest satisfying solution ? >> >> I'm not sure I _quite_ understand the problem, but why >> wouldn't you have the same potential problem with some >> other library (without libthread)? I'll have to go back >> and read the beginning of the thread - I just kinda came >> in at the end. > > Sure, for appropriate value of any. If you mean whether the same problem > would arise for any threading library that supplies locking implementation > for rtld, then certainly yes. I looked over and patched only libthr > since this is the only survived library for now. What I mean is, is fixing libthr a solution that will work for cases? Or, is libthr doing something wrong? I can't really see that it is. libthr assumes that everything is single-threaded (or serialized, I guess) before a thread is created. I am looking at this thread: http://docs.freebsd.org/cgi/getmsg.cgi?fetch=5235+0+current/freebsd-threads Where is the corresponding unlock for the wlock_acquire()? I guess this is the problem. When would this normally be released (without libthr being linked in)? Also, the __isthreaded flag is used in libc to avoid taking locks unless necessary. So if you have a single threaded application that is also linked with libthr, you don't pay the penalty of locking overhead. Lots of 3rd-party libraries link with a threads library, so an application may not even know it is "threaded". > > Anyway, I do not insist on the proposed solution, and definitely > prefer the change that is well aligned with libthr architecture. I'm not arguing anything, I just don't know that the problem lies within lib<insert thread library here>. Of course, the rtld init stuff could be pulled out and done in thread initialization instead of thr_setthreaded(). That doesn't leave much in thr_setthreaded, and it also adds locking overhead into rtld for single-threaded programs that are linked with libthr... -- DE
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