As you might already know, the Ruby interpreter you’re (probably) using (the one at ruby-lang.org) know as MRI, for Matz Ruby Interpreter, is written in C. The VM is entirely written in C and most of the standard libraries too. So it seems that the way to make code run faster is really to dive into C.

Now I hear you yell with your ears all red, eyes full of blood and a big vein pumping on your forehead: But it will be unmaintainable!

If everything seems under control, you’re not going fast enough

– Mario Andretti

The hard part is that the C API of MRI lacks documentation. You either have to search through the mailinglist, look at other people’s code or try to guess from Ruby’s code. I recently ported a bit of code from Ruby to C and here are a couple of Ruby to C mapping that might help you.

If you’ve never written or looked at a Ruby extension before, I suggestion reading Peter Cooper excellent and very simple tutorial on how to set things up.

Objects are VALUEs

my_var = nil this_is_true = true some_fixnum = 1 VALUE my_var = Qnil; VALUE this_is_true = Qtrue; VALUE some_fixnum = INT2FIX( 1 );

Strings

string = " hi " VALUE string = rb_str_new2( " hi " ); /* Ruby string to C string */ char *s = RSTRING_PTR(str); int len = RSTRING_LEN(str);

Object to C struct

In C you’ll probably want to store your data in a struct. Ruby provide some things to wrap a struct inside a Ruby object. Also, since Ruby is not aware of the stuff created in the C world we have to be pretty explicit about everything.

module MyModule class MyClass def close @ closed = true end end end In C /* This is called by Ruby GC when the object is freed * so free all resources used here. We hook it up * in the Data_Wrap_Struct call down there. */ void my_obj_free(my_struct_t *s) { free (s); } /* Called by Ruby then and instance of your class is created * hooked by rb_define_alloc_func. */ VALUE my_obj_all oc (VALUE klass) { my_struct_t *s = ALLOC_N(my_struct_t, 1 ); /* This stores the struct inside the Ruby object, so you * can get the struct back on each method call. */ return Data_Wrap_Struct(klass, NULL , my_obj_free, s); } /* The actual MyClass#close method, first argument is the * instance object. It's hook into our class by the rb_define_method * call in Init_ */ VALUE my_obj_clo se (VALUE self) { my_struct_t *s; /* This is where we get the struct back from the Ruby object */ Data_Get_Struct(self, my_struct_t, s); s->closed = 1 ; } /* Init_* is magically called by Ruby to bootstrap your extension, * it's like a main function if you will. */ void Init_name_of_your_extension() { VALUE mMyModule = rb_define_module( " MyModule " ); VALUE cMyClass = rb_define_class_under(mMyModule, " MyClass " , rb_cObject); rb_define_alloc_func(cMyClass, my_obj_alloc); rb_define_method(cMyClass, " close " , my_obj_close, 0 ); } Calling methods

obj. method_name result = begin obj. method_name (arg) rescue # … end rb_funcall(obj, rb_intern( " method_name " ), 0 ); /* if an error is raised, result will be set to Qundef */ VALUE result = rb_funcall_rescue(obj, rb_intern( " method_name " ), 1 , arg);

Blocks

my_ary. each do | i | puts i end VALUE i_ea ch (VALUE elem, VALUE *obj) { /* elem is the yielded object and obj is a pointer to obj down there v */ printf ( " %d

" , FIX2INT(elem)); return Qnil; } rb_iterate(rb_each, my_ary, i_each, (VALUE) obj);

Error handling

raise ArgumentError , " ... " rb_raise(rb_eArgError, " ... " ); /* To raise an error corresponding to the one in errno */ rb_sys_fail( " oops " );

Garbage Collection

When creating Ruby objects in the C world, Ruby is not aware of the scope of each, it’s impossible to track when a variable is used and when it’s not, so it’s impossible for the garbage collector to know when do leave or sweep objects. If you create a long live object, that will persist for several method calls you have to tell Ruby’s garbage collector when it’s in use and when you’re finished with it. If you don’t, Ruby GC will free your variable in the worst possible time, ending up with unthinkable tragedies around the world, leaving you homeless and poor for all eternity.