[ruby-core:23933] Stack size detection algorithm

Hi!

When debugging the stack overflow bug in ruby 1.8.7 on FreeBSD, I notices t=
hat
its stack detection algoritm doesn't work properly in pthreads case,
as it still uses the value returned by getrlimit as the stack maximum
size.  However, this value would not work on FreeBSD and probably other
OSes, as in pthreads case the main thread's stack size is much lower than
the stack size limit for the whole process.

I attached the patch that adds an additional check for stack size in pthread
case via pthread_attr_getstacksize if pthreads is enabled.  If the value
returned by pthread functions is lower than stack size limit, this value
will be used instead.  I also moved these checks into the separate function
to eliminate code duplication.

The other modification I made adds proactive check for stack size available.
Currently, ruby reserves up to 1/5 of available stack size for safeguard
purposes, and performs stack limit checks only each 256th call of rb_call0.
When the available stack size is too small, 1/5 of it may not be enough for
next 256 calls to rb_call0 to complete for ruby to detect overflow.  The
code I added measures how much of stack size was consumed since the previous
check and if the stack size available is lower than this value the exception
will be generated.

I attached patched to configure.in and gc.c to the mail.

--=20
Stanislav Sedov
ST4096-RIPE