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List:       hpux-devtools
Subject:    RE: HPUX-DEVTOOLS: mixing threaded and non-threaded code
From:       "SAILER,LEE (HP-USA,ex1)" <lee_sailer () hp ! com>
Date:       2001-05-31 20:25:35
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> Hello -
> 
> I would like to find a definitive answer on whether it is 
> safe to have a
> library that is compiled with threading enabled, linked with 
> other code that
> was compiled without it. Is there a document that has 
> information on this?
> The couple manuals I found on threading did not cover this issue.
> 

It often works out OK.  however, the general answer is that if any library
is multi-threaded then all the rest of the objects must be "thread safe".
the most common case is that programmers are linking to a vendor provided
database library that is multi-threaded, but because the programmer never
actually uses pthread_create(), he or she believes that thread safety is
irrelevant.  BZZZT.  Wrong.  Sorry.  Please play again.

I am not the final authority on this issue, but I run across it all the
time.

I can suggest some minimum safety measures.

1.  #include <pthread.h> in every source file, preferably first.
2.  -DPTHREAD_DRAFT4 if old (DCE/DMA) HP-UX threads are in play.
3.  -D_POSIX_C_SOURCE=199506L for all source files.  Best is to put it in
master .h files directly.
4.  If aCC is in play, there are some more -D's required.  The newest aCC
has a +mt option (I think) that turns them all on.
5.  Be careful of link order.  libc must always come after libpthread (or
libcma).  Set LDOPTS=-v to get a verbose link and examine the output
carefully.
6.  Use thread safe API's where available, such as getlogin_r() in place of
getlogin()

NOTE:  The symptom most often related to thread UNsafety is the occasional
mysterious core dump of a process that otherwise seems to work most the
time.  Sound familiar?

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