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POCalling Ruby function from C++ in a loop results in "stack level too deep"
 

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  1. POCalling Ruby function from C++ in a loop results in "stack level too deep"
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    <p>I'm trying to run blocks of Ruby code from C++. I have two Ruby functions, one called Init(), and one called Loop(). The problem I have is that I can only Loop() so many times before I get a "stack level too deep" from SystemStackError. My Ruby code is not recursive as far as I can tell. As you can see, so far this Ruby code is just for a proof-of-concept and loaded with nothing but debug-style stuff and blinking a light on a panel. Here's the Ruby code:</p> <pre><code>def Init() puts 'Hello from script\'s Init()!' $i = 0 $p = Panel.new $p.Debug $p.Extinguish( "Running" ) $p.Illuminate( "Fault" ) end def Loop() puts 'Hello from Loop!' + $i.to_s $i += 1 puts $p $p.Debug $p.Illuminate( "Running" ) if $i % 2 == 1 $p.Extinguish( "Running" ) if $i % 2 != 1 end </code></pre> <p>My implementation of Panel in C++ is:</p> <pre><code>ruby_init(); VALUE cPanel; cPanel = rb_define_class( "Panel", rb_cObject ); rb_define_singleton_method( cPanel, "new", (RubyMethod*)&amp;StaticRubyNew, 0 ); rb_define_method( cPanel, "Debug", (RubyMethod*)&amp;StaticRubyDebug, 0 ); rb_define_method( cPanel, "Extinguish", (RubyMethod*)&amp;StaticRubyExtinguish, 1 ); rb_define_method( cPanel, "Illuminate", (RubyMethod*)&amp;StaticRubyIlluminate, 1 ); </code></pre> <p>I call the script functions as follows:</p> <pre><code>rb_eval_string( program ); rb_funcall( Qnil, rb_intern( "Init" ), 0, NULL ); // In a 200ms loop: rb_funcall( Qnil, rb_intern( "Loop" ), 0, NULL ); </code></pre> <p>Nothing worked until I wrote a (suspect) implementation of <strong>new</strong>:</p> <pre><code>VALUE MainWidget::RubyNew( VALUE clas ) { // Looks like we have to return *something* instead of Qnil, even if I // don't have anything to wrap yet. const char* s = "Dude"; VALUE tdata = Data_Wrap_Struct( clas, StaticRubyMark, StaticRubyFree, const_cast&lt;char*&gt;(s) ); return tdata; } </code></pre> <p>RubyMark and RubyFree don't do anything, and RubyDebug, RubyIlluminate, etc. don't do anything remarkable either for the problem at hand.</p> <p>I've tried wrapping Init and Loop in a class as class methods, so I can call rb_funcall() with a real receiver. I've tried getting a backtrace by calling through rb_protect() (the backtrace appears empty). Nothing online seems to have the secret for loading the script as a string, so rb_eval_string() is a guess. rb_load_file() doesn't work either.</p> <p>Why does this cause stack problems? I can edit my Ruby script, adding or removing code, and the stack blows after executing various numbers of loops. The number of loops that I can execute has no discernible relationship to the number of lines. If I remove a line, I might get 45 loops. If I remove another, I might get over 2000. What am I doing wrong?</p> <p>A little more code in light of the response below--this is to give C++ methods to Ruby API calls (which expect C-style functions):</p> <pre><code>typedef VALUE (RubyMethod)(...); extern "C" /*static*/ VALUE StaticRubyNew( VALUE self ) { return MainWidget::M_this-&gt;RubyNew( self ); } </code></pre>
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    1. COWell I'm a little closer--I pulled all this out into a purely C driven app and it runs for at least 500,000 loops (before I killed it). It must be something I'm doing wrong with a C++ to C interface.
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