f30ce1fe97
For host VM code, we use plain reference counting, where cloning increments
the reference count, and dropping decrements it. We can avoid many of the
on-stack increment/decrement operations that typically plague the
performance of reference counting via Rust's ownership and borrowing system.
Moving a `VMExternRef` avoids mutating its reference count, and borrowing it
either avoids the reference count increment or delays it until if/when the
`VMExternRef` is cloned.
When passing a `VMExternRef` into compiled Wasm code, we don't want to do
reference count mutations for every compiled `local.{get,set}`, nor for
every function call. Therefore, we use a variation of **deferred reference
counting**, where we only mutate reference counts when storing
`VMExternRef`s somewhere that outlives the activation: into a global or
table. Simultaneously, we over-approximate the set of `VMExternRef`s that
are inside Wasm function activations. Periodically, we walk the stack at GC
safe points, and use stack map information to precisely identify the set of
`VMExternRef`s inside Wasm activations. Then we take the difference between
this precise set and our over-approximation, and decrement the reference
count for each of the `VMExternRef`s that are in our over-approximation but
not in the precise set. Finally, the over-approximation is replaced with the
precise set.
The `VMExternRefActivationsTable` implements the over-approximized set of
`VMExternRef`s referenced by Wasm activations. Calling a Wasm function and
passing it a `VMExternRef` moves the `VMExternRef` into the table, and the
compiled Wasm function logically "borrows" the `VMExternRef` from the
table. Similarly, `global.get` and `table.get` operations clone the gotten
`VMExternRef` into the `VMExternRefActivationsTable` and then "borrow" the
reference out of the table.
When a `VMExternRef` is returned to host code from a Wasm function, the host
increments the reference count (because the reference is logically
"borrowed" from the `VMExternRefActivationsTable` and the reference count
from the table will be dropped at the next GC).
For more general information on deferred reference counting, see *An
Examination of Deferred Reference Counting and Cycle Detection* by Quinane:
https://openresearch-repository.anu.edu.au/bitstream/1885/42030/2/hon-thesis.pdf
cc #929
Fixes #1804
93 lines
2.4 KiB
TOML
93 lines
2.4 KiB
TOML
[package]
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name = "wasmtime-cli"
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version = "0.18.0"
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authors = ["The Wasmtime Project Developers"]
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description = "Command-line interface for Wasmtime"
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license = "Apache-2.0 WITH LLVM-exception"
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documentation = "https://bytecodealliance.github.io/wasmtime/cli.html"
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categories = ["wasm"]
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keywords = ["webassembly", "wasm"]
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repository = "https://github.com/bytecodealliance/wasmtime"
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readme = "README.md"
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edition = "2018"
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default-run = "wasmtime"
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[lib]
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doctest = false
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[[bin]]
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name = "wasmtime"
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path = "src/bin/wasmtime.rs"
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doc = false
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[dependencies]
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# Enable all supported architectures by default.
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wasmtime = { path = "crates/wasmtime", version = "0.18.0", default-features = false }
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wasmtime-debug = { path = "crates/debug", version = "0.18.0" }
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wasmtime-environ = { path = "crates/environ", version = "0.18.0" }
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wasmtime-jit = { path = "crates/jit", version = "0.18.0" }
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wasmtime-obj = { path = "crates/obj", version = "0.18.0" }
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wasmtime-wast = { path = "crates/wast", version = "0.18.0" }
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wasmtime-wasi = { path = "crates/wasi", version = "0.18.0" }
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wasi-common = { path = "crates/wasi-common", version = "0.18.0" }
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structopt = { version = "0.3.5", features = ["color", "suggestions"] }
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object = { version = "0.19", default-features = false, features = ["write"] }
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anyhow = "1.0.19"
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target-lexicon = { version = "0.10.0", default-features = false }
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pretty_env_logger = "0.4.0"
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file-per-thread-logger = "0.1.1"
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wat = "1.0.18"
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libc = "0.2.60"
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log = "0.4.8"
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rayon = "1.2.1"
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humantime = "1.3.0"
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[dev-dependencies]
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env_logger = "0.7.1"
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filecheck = "0.5.0"
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more-asserts = "0.2.1"
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tempfile = "3.1.0"
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test-programs = { path = "crates/test-programs" }
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wasmtime-fuzzing = { path = "crates/fuzzing" }
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wasmtime-runtime = { path = "crates/runtime" }
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[build-dependencies]
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anyhow = "1.0.19"
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[profile.release.build-override]
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opt-level = 0
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[workspace]
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members = [
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"cranelift",
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"crates/c-api",
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"crates/fuzzing",
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"crates/misc/run-examples",
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"crates/misc/rust",
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"crates/wiggle",
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"examples/fib-debug/wasm",
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"examples/wasi/wasm",
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"fuzz",
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]
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[features]
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default = ["jitdump", "wasmtime/wat"]
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lightbeam = [
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"wasmtime-environ/lightbeam",
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"wasmtime-jit/lightbeam",
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"wasmtime-wast/lightbeam",
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"wasmtime/lightbeam",
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]
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jitdump = ["wasmtime/jitdump"]
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vtune = ["wasmtime/vtune"]
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[badges]
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maintenance = { status = "actively-developed" }
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[[test]]
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name = "host_segfault"
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harness = false
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[patch.crates-io]
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backtrace = { git = "https://github.com/rust-lang/backtrace-rs.git" }
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