glossary.md

Ruby Internals Glossary

Just a list of acronyms I've run across in the Ruby source code and their meanings.

Term	Definition
BIN	Basic Instruction Name. Used as a macro to reference the YARV instruction. Converts pop into YARVINSN_pop.
bop	Basic Operator. Relates to methods like Integer plus and minus which can be optimized as long as they haven't been redefined.
cc	Call Cache. An inline cache structure for the call site. Stored in the cd
cd	Call Data. A data structure that points at the ci and the cc. iseq objects points at the cd, and access call information and call caches via this structure
cfp	Control Frame Pointer. Represents a Ruby stack frame. Calling a method pushes a new frame (cfp), returning pops a frame. Points at the pc, sp, ep, and the corresponding iseq
ci	Call Information. Refers to an rb_callinfo struct. Contains call information about the call site, including number of parameters to be passed, whether it they are keyword arguments or not, etc. Used in conjunction with the cc and cd.
cref	Class reference. A structure pointing to the class reference where klass_or_self, visibility scope, and refinements are stored. It also stores a pointer to the next class in the hierarchy referenced by rb_cref_struct * next. The Class reference is lexically scoped.
CRuby	Implementation of Ruby written in C
cvar	Class Variable. Refers to a Ruby class variable like @@foo
dvar	Dynamic Variable. Used by the parser to refer to local variables that are defined outside of the current lexical scope. For example def foo; bar = 1; -> { p bar }; end the "bar" inside the block is a dvar
ec	Execution Context. The top level VM context, points at the current cfp
ep	Environment Pointer. Local variables, including method parameters are stored in the ep array. The ep is pointed to by the cfp
GC	Garbage Collector
gvar	Global Variable. Refers to a Ruby global variable like $$, etc
ICLASS	Internal Class. When a module is included, the target class gets a new superclass which is an instance of an ICLASS. The ICLASS represents the module in the inheritance chain.
ifunc	Internal FUNCtion. A block implemented in C.
iseq	Instruction Sequence. Usually "iseq" in the C code will refer to an rb_iseq_t object that holds a reference to the actual instruction sequences which are executed by the VM. The object also holds information about the code, like the method name associated with the code.
insn	Instruction. Refers to a YARV instruction.
insns	Instructions. Usually an array of YARV instructions.
ivar	Instance Variable. Refers to a Ruby instance variable like @foo
imemo	Internal Memo. A tagged struct whose memory is managed by Ruby's GC, but contains internal information and isn't meant to be exposed to Ruby programs. Contains various information depending on the type. See the imemo_type enum for different types.
JIT	Just In Time compiler
lep	Local Environment Pointer. An ep which is tagged VM_ENV_FLAG_LOCAL. Usually this is the ep of a method (rather than a block, whose ep isn't "local")
local	Local. Refers to a local variable.
me	Method Entry. Refers to an rb_method_entry_t struct, the internal representation of a Ruby method.
MRI	Matz's Ruby Implementation
pc	Program Counter. Usually the instruction that will be executed next by the VM. Pointed to by the cfp and incremented by the VM
sp	Stack Pointer. The top of the stack. The VM executes instructions in the iseq and instructions will push and pop values on the stack. The VM updates the sp on the cfp to point at the top of the stack
svar	Special Variable. Refers to special local variables like $~ and $_. See the getspecial instruction in insns.def
VALUE	VALUE is a pointer to a ruby object from the Ruby C code.
VM	Virtual Machine. In MRI's case YARV (Yet Another Ruby VM)
WB	Write Barrier. To do with GC write barriers
WC	Wild Card. As seen in instructions like getlocal_WC_0. It means this instruction takes a "wild card" for the parameter (in this case an index for a local)
YARV	Yet Another Ruby VM. The virtual machine that CRuby uses
ZOMBIE	A zombie object. An object that has a finalizer which hasn't been executed yet. The object has been collected, so is "dead", but the finalizer hasn't run yet so it's still somewhat alive.