Re: kgio_ext.so: [BUG] constant not a symbol or string

[Eric Wong <normalperson@yhbt.net>]

Christopher Rigor <crigor@gmail.com> wrote:
> When I start sidekiq from the command line, it runs correctly. When it is
> started from monit, I get kgio_ext.so: [BUG] constant not a symbol or
> string.

Can you verify this is the same instance of sidekiq and loading the same
libraries from the same paths?  Also, are you using RVM or rbenv or
similar?  Can you reproduce the issue without those?

> I'm using kgio 2.8.0 and ruby 2.0.0 p353.
> 
> I know monit doesn't set some environment variables but I didn't expect to
> encounter an issue with Ruby internals if an environment variable is
> missing.
> 
> Based on the backtrace "kgio-2.8.0/lib/kgio_ext.so(init_kgio_tryopen+0x1a9)
> [0x7fe93d120359]" I found the code where the error came from.
> http://repo.or.cz/w/kgio.git/blob/8be51237720fd18cb45188f29c717bbac0ca1964:/ext/kgio/tryopen.c#l173
> 
> 1. Is this an error on kgio?

Unlikely :>

> 2. Did I give enough information to pinpoint the issue?

Not yet, but we'll get there.

> 3. How can I debug this? What tools do you use for this kind of problems?

I suspect something is mixed up with the installation/loading via monit.
Most likely, the kgio you're loading is for a different version of Ruby
than what you're running.  Or (unlikely) something is monkeypatching
Errno.constants to return bogus output...

Since you're running Ruby 2.0, you should see an array of symbols
(and nothing else) from the following command:

	ruby -e 'p Errno.constants'

You can also try dumping Errno.constants at various places in the
sidekiq code.  Sorry, I'm not familiar with sidekiq; but hopefully
it's not mangling Errno.constants output under monit somehow.

Also, the following patch should give you a little more debug output:

--- a/ext/kgio/tryopen.c
+++ b/ext/kgio/tryopen.c
@@ -173,7 +173,12 @@ void init_kgio_tryopen(void)
 		switch (TYPE(err)) {
 		case T_SYMBOL: const_id = SYM2ID(err); break;
 		case T_STRING: const_id = rb_intern(RSTRING_PTR(err)); break;
-		default: rb_bug("constant not a symbol or string");
+		default: {
+			VALUE i = rb_inspect(err);
+			const char *s = StringValueCStr(i);
+
+			rb_bug("constant not a symbol or string: %s", s);
+			}
 		}
 
 		error = rb_const_get(rb_mErrno, const_id);