Testcase (was: Stack checking, core dumps, and embedding R)

Sorry about all the noise, but I'm slightly irritated by the absence of
reactions of any kind, while the time to the release is ticking away.

Attached you will find a testcase for the problem. Likely the error will
only show up on linux, due to the

	#if defined(linux)
	    R_CStackStart = (uintptr_t) __libc_stack_end;
	#elif ...

in unix/system.c . Also the error may not be 100% reproducible, depending
on where exactly the stack for the worker thread is allocated, but at least
for me it has triggered every single time I tried it (recent debian
unstable on a Pentium M, for reference).

For your convenience, if you place the testcase in tests/Embedding of your
R source tree, here are the lines needed to compile and run:

gcc -I. -I../../src/include -I../../src/include -I/usr/local/include
-DHAVE_CONFIG_H   -g -O2 -std=gnu99 -c threadEmbed.c -o threadEmbed.o

../../bin/R CMD LINK gcc -o threadEmbed
threadEmbed.o -L../../lib -lR -lpthread

(R_HOME=../..; export R_HOME; ./threadEmbed --silent)

Once again, I don't know how many embedding applications are affected by
this, but it is absolutely fatal for rkward, at least. The proposed patch,
cited again, below, fixes the problem.

Regards
Thomas

On Monday 17 April 2006 15:20, Thomas Friedrichsmeier wrote:

Excuse me please, for being impatient, but I'm worried this issue may not
be considered important enough to be fixed in R 2.3.0 at this late point
of time. So let me re-state this:

In the current state, R will *not work at all* when run in a thread on
linux.

I do not know how many embedding applications run R in a separate thread,
and are affected by this. I know that at least rkward does, and it will
not run.

Reconsidering the proposals I made yesterday, after some sleep, let me
propose this corrected fix (insert into src/unix/system.c, at line 179,
right above "if(R_CStackStart == -1) R_CStackLimit = -1; /* never set
*/"):

    if (abs (R_CStackStart - (uintptr_t) &i) > 20000) {
	/* Very unlikely we're this far away from the stack start at this
	point in the code. Disable checking */
	R_CStackStart = -1;
    }

For all I care, set the safety margin to 50000 or even more. This
heuristic is only meant to catch cases where the detected value for
R_CStackStart is *obviously wrong*, most importantly in case of threads.

In this case all it will do is to disable the check. I can see no other
side-effect.

Once again, excuse me for being impatient, but *please* consider this for
inclusion in R 2.3.0.

Regards
Thomas