arkcompiler_runtime_core/docs/glossary.md

Glossary

Introduction

During the development of Panda Runtime, we faced the fact that terminology related to the development of compilers and interpreters is confusing in some cases. This document describes what the terms used mean.

Core terminology

• AOT stands for Ahead-Of-Time. In compilers, terms "ahead-of-time compilation" and "AOT compilation" are used to indicate that the source code or bytecode is compiled before actual execution. In case of Panda Runtime, AOT compilation is used to compile Panda Bytecode into native machine code to reduce runtime overhead from reading and compiling bytecode. See https://en.wikipedia.org/wiki/Ahead-of-time_compilation.
• Bytecode. See Panda Bytecode.
• Compiler is a tool that performs source code or bytecode translation, optimization and native code generation.
• IR stands for Intermediate Representation. IR is an internal compiler data structure used to represent input program and usually designed for analysis and optimization. See https://en.wikipedia.org/wiki/Intermediate_representation.
• ISA stands for Instruction Set Architecture. See Panda Bytecode and https://en.wikipedia.org/wiki/Instruction_set_architecture.
• JIT stands for Just-In-Time. In compilers, terms "just-in-time compilation" and "JIT compilation" are used to indicate that the source code or bytecode is compiled during program execution. In case of Panda Runtime, JIT compilation is used to compile Panda Bytecode into native machine code to reduce overhead from interpreting bytecode. See https://en.wikipedia.org/wiki/Just-in-time_compilation.
• Panda Assembler is a tool that translates Panda Assembly Language to Panda Binary File.
• Panda Assembly Language is a low-level programming language retaining very strong correspondence between the instructions in the language and Panda Bytecode instructions. See Assembly Format.
• Panda Binary File or Panda File or PF is a binary representation of Panda Bytecode. See File Format.
• Panda Bytecode or PBC is a portable hardware-independent instruction set designed for compactness and efficient execution by Panda Runtime. See https://en.wikipedia.org/wiki/Bytecode.
• Runtime is a runtime system, also called runtime environment.

Memory management terms

• Allocator is a part of the system that servicing allocation and deallocation requests.
• Card is a division of memory with some fixed size. Card size usually smaller than a page.
• Card table used for marking cards. In general, it has one bit or byte (a byte used to improve performance of GC barrier) for one card. It can be used by both generational and concurrent collectors. It can be used for tracking references from tenured generation to the young generation and for tracking modified references during concurrent phase of GC.
• Compacting GC is a GC which compacts live objects to reduce fragmentation.
• Conservative GC or non-precise GC works with ambiguous references, i.e. it treats anything inside object boundaries like a reference. Opposite term: Precise GC.
• Full GC is cleaning the entire Heap.
• Garbage collection is also known as automatic memory management, is the automatic recycling of dynamically allocated memory.
• Garbage collector performs garbage collection. Garbage collector recycles memory that it can prove will never be used again.
• GC stands for Garbage collector or sometimes for Garbage collection.
• Minor GC in general it is garbage collection worked over Young generation space (it includes survivor Eden and Survivor spaces).
• Major GC in general it is garbage collection worked over Tenured/Old generation space. Sometimes it is triggered by Minor GC, so it is impossible to separate them(see Full GC).
• Safepoint is a range of execution where the state of the executing thread is well described. Safepoint is used as a point at which we can safely stop the thread, and at this point, all references on the stack are mapped (i.e., it is known when we have an object on the stack or not). Mutator is at a known point in its interaction with the heap. It means that all objects which are currently in use are known and we know how to get value for each of their fields.
• Precise GC deals only with exact/sure references, i.e. it knows object layout and can extract references to the objects. Opposite term: Conservative GC.
• Semi-space compaction is a compaction algorithm when memory is split to the two equal spaces (one is empty and one used for allocation) and we just copy objects from one space to another using bump pointer allocator.
• STW stands for stop the world, used in context of stop the world pauses forced by GC - GC force to stop execution of code (interpreted,AOTed or JITed) to make exclusively some operations.
• TLAB stands for Thread Local Allocation Buffer - buffer used exclusively for allocations in the thread (no lock required).
• white object is an object non visited by GC(at the end of GC white objects will be reclaimed)
• gray object is reachable/alive object, but still should be scanned by GC (to process all fields with reference type)
• black object is reachable/alive object and scanned by GC
• throughput is % of time not spent in GC over a long period of time(sometimes GC throughput uses as % time spent in GC over a long period of time)