Using define in multiple threads?

[Linas Vepstas]

Is it "safe" or "legal" to use define in multiple threads?

I am currently looking at an infinite loop in guile, it looks
like there's a pair with cdr pointing to itself.  The pair is
a hashtable bucket. I'm reading through hashtab.c
and see no locking at all, and so it seems probable that
this circular bucket list was created in a race between
two threads inserting into the same hash table.

Now, the test case which triggers this does nothing
other than defines --  it loads a set of files, one per thread,
and, for good measure, I reloaded these over and over.
So typically, one will have the same function being
redefined over and over, typically in different threads.
The same function might be getting defined "simultaneously"
in different threads, even.

So-- I was assuming that this would be an inherently
"safe" operation ... but maybe its not? Is there some funky
semantics to define in a multi-threaded environment?

--linas