On 10/26/2004 6:13 PM, Bruce Momjian wrote:

> I believe Slony always needs threading, it just can be used even if the
> OS doesn't fully support all thread-safe functions, so on 8.0 you use
> --thread_safety_force.  Jan, is that correct?

Yes.

Slony allways uses pthreads and therefore it requires that on platforms, 
where the reentrant libc has a different definition for several global 
symbols (like errno), libpq is compiled with pthread compiler flags. If 
that actually leads to a "thread-safe" libpq or not is completely 
irrelevant, because Slony does not need the libpq to be thread-safe.

A good example for what happens is Solaris. If libpq is compiled without 
-pthreads, then "errno" is just the good old "extern int errno;". But if 
it is compiled with -pthreads, then "errno" is #defined to dereferencing 
the result of a function, like "*(__thread_errno())" and that function 
returns the thread specific error variable and int*. Since slon is 
compiled with pthreads, it links against the reentrant libc which places 
error codes in the thread specific error variable. Why in devils name 
that reentrant libc also has a global errno variable at all is a secret 
to me and probably the last developer who knew that has left Sun 5 years 
ago, but it has one and leaves it just zero all the time. Since it has 
one, the extern reference errno from the non -pthread compiled libpq is 
resolved just fine ... to a location of 4 wasted, meaningless bytes.


Jan

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