Wasmer Features

The Wasmer WebAssembly runtime provides various features for users and developers:

• Backends: Wasmer supports multiple compiler backends: Singlepass, Cranelift and LLVM. Each of these have different tradeoffs of compilation speed vs runtime speed;

• Caching: compiled WebAssembly modules can be reused so subsequent runs of a Wasm file will have very little start up time;

• Metering: computation time and other resources can be monitored and limits set to control how the Wasm code runs. This is also known as "gas metering";

• WebAssembly Features:

  • Multi-value return: return multiple values from functions making data transfer between host and guest simpler;

  • SIMD: Single Instruction, Multiple data: do heavy number crunching more quickly and/or with lower power usage.

• ABIs: it allows running different types of programs compiled to WebAssembly, with ABIs such as:

  • Emscripten

  • WASI

Support of features by Backend

	Singlepass	Cranelift	LLVM
Caching	✅	✅	✅
Emscripten	✅	✅	✅
Metering	✅	✅	✅
Multi-value return	✅	✅	✅
SIMD	⬜	⬜	✅
WASI	✅	✅	✅
WASMER_BACKTRACE	✅	⬜	⬜

Legend

• ✅ Supported

• 🔄 In the works

• ⬜ Not yet supported (please ping us if you need this feature!)

Support by Operating System

	GNU Linux	Mac OSX	Windows NT
Cranelift Backend	✅	✅	✅
LLVM Backend	✅	✅	✅
Singlepass Backend	✅	✅	#347
WASI	✅	✅	✅*

• poll_fd is not fully implemented for Windows yet

Language integration

TODO: define a set of features that are relevant and mark them here

Current ideas:

• Callbacks

• Metering

• Caching

TODO: expand this table, it's focused on new features that we haven't implemented yet and doesn't list all language integrations

	Rust	C / C++	Go	Python	Ruby
Terminate in host call	✅	⬜	⬜	⬜	⬜
WASI	✅	✅	🔄	⬜	⬜
WASI FS API	✅	⬜	⬜	⬜	⬜