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use crate::signatures::SignatureRegistry;
use crate::{Config, Trap};
use anyhow::Result;
use std::sync::Arc;
#[cfg(feature = "cache")]
use wasmtime_cache::CacheConfig;
use wasmtime_jit::Compiler;
use wasmtime_runtime::{debug_builtins, InstanceAllocator};
/// An `Engine` which is a global context for compilation and management of wasm
/// modules.
///
/// An engine can be safely shared across threads and is a cheap cloneable
/// handle to the actual engine. The engine itself will be deallocated once all
/// references to it have gone away.
///
/// Engines store global configuration preferences such as compilation settings,
/// enabled features, etc. You'll likely only need at most one of these for a
/// program.
///
/// ## Engines and `Clone`
///
/// Using `clone` on an `Engine` is a cheap operation. It will not create an
/// entirely new engine, but rather just a new reference to the existing engine.
/// In other words it's a shallow copy, not a deep copy.
///
/// ## Engines and `Default`
///
/// You can create an engine with default configuration settings using
/// `Engine::default()`. Be sure to consult the documentation of [`Config`] for
/// default settings.
#[derive(Clone)]
pub struct Engine {
inner: Arc<EngineInner>,
}
struct EngineInner {
config: Config,
compiler: Compiler,
allocator: Box<dyn InstanceAllocator>,
signatures: SignatureRegistry,
}
impl Engine {
/// Creates a new [`Engine`] with the specified compilation and
/// configuration settings.
pub fn new(config: &Config) -> Result<Engine> {
// Ensure that wasmtime_runtime's signal handlers are configured. This
// is the per-program initialization required for handling traps, such
// as configuring signals, vectored exception handlers, etc.
wasmtime_runtime::init_traps(crate::module::GlobalModuleRegistry::is_wasm_pc);
debug_builtins::ensure_exported();
let allocator = config.build_allocator()?;
let registry = SignatureRegistry::new();
Ok(Engine {
inner: Arc::new(EngineInner {
config: config.clone(),
compiler: config.build_compiler(allocator.as_ref()),
allocator,
signatures: registry,
}),
})
}
/// Eagerly initialize thread-local functionality shared by all [`Engine`]s.
///
/// Wasmtime's implementation on some platforms may involve per-thread
/// setup that needs to happen whenever WebAssembly is invoked. This setup
/// can take on the order of a few hundred microseconds, whereas the
/// overhead of calling WebAssembly is otherwise on the order of a few
/// nanoseconds. This setup cost is paid once per-OS-thread. If your
/// application is sensitive to the latencies of WebAssembly function
/// calls, even those that happen first on a thread, then this function
/// can be used to improve the consistency of each call into WebAssembly
/// by explicitly frontloading the cost of the one-time setup per-thread.
///
/// Note that this function is not required to be called in any embedding.
/// Wasmtime will automatically initialize thread-local-state as necessary
/// on calls into WebAssembly. This is provided for use cases where the
/// latency of WebAssembly calls are extra-important, which is not
/// necessarily true of all embeddings.
pub fn tls_eager_initialize() -> Result<(), Trap> {
wasmtime_runtime::tls_eager_initialize().map_err(Trap::from_runtime)
}
/// Returns the configuration settings that this engine is using.
#[inline]
pub fn config(&self) -> &Config {
&self.inner.config
}
pub(crate) fn compiler(&self) -> &Compiler {
&self.inner.compiler
}
pub(crate) fn allocator(&self) -> &dyn InstanceAllocator {
self.inner.allocator.as_ref()
}
#[cfg(feature = "cache")]
pub(crate) fn cache_config(&self) -> &CacheConfig {
&self.config().cache_config
}
/// Returns whether the engine `a` and `b` refer to the same configuration.
pub fn same(a: &Engine, b: &Engine) -> bool {
Arc::ptr_eq(&a.inner, &b.inner)
}
pub(crate) fn signatures(&self) -> &SignatureRegistry {
&self.inner.signatures
}
/// Ahead-of-time (AOT) compiles a WebAssembly module.
///
/// The `bytes` provided must be in one of two formats:
///
/// * A [binary-encoded][binary] WebAssembly module. This is always supported.
/// * A [text-encoded][text] instance of the WebAssembly text format.
/// This is only supported when the `wat` feature of this crate is enabled.
/// If this is supplied then the text format will be parsed before validation.
/// Note that the `wat` feature is enabled by default.
///
/// This method may be used to compile a module for use with a different target
/// host. The output of this method may be used with
/// [`Module::deserialize`](crate::Module::deserialize) on hosts compatible
/// with the [`Config`] associated with this [`Engine`].
///
/// The output of this method is safe to send to another host machine for later
/// execution. As the output is already a compiled module, translation and code
/// generation will be skipped and this will improve the performance of constructing
/// a [`Module`](crate::Module) from the output of this method.
///
/// [binary]: https://webassembly.github.io/spec/core/binary/index.html
/// [text]: https://webassembly.github.io/spec/core/text/index.html
pub fn precompile_module(&self, bytes: &[u8]) -> Result<Vec<u8>> {
const USE_PAGED_MEM_INIT: bool = cfg!(all(feature = "uffd", target_os = "linux"));
#[cfg(feature = "wat")]
let bytes = wat::parse_bytes(&bytes)?;
let (_, artifacts, types) = wasmtime_jit::CompilationArtifacts::build(
&self.inner.compiler,
&bytes,
USE_PAGED_MEM_INIT,
)?;
crate::module::SerializedModule::from_artifacts(&self.inner.compiler, &artifacts, &types)
.to_bytes()
}
}
impl Default for Engine {
fn default() -> Engine {
Engine::new(&Config::default()).unwrap()
}
}
#[cfg(test)]
mod tests {
use crate::{Config, Engine, Module, OptLevel};
use anyhow::Result;
use tempfile::TempDir;
#[test]
fn cache_accounts_for_opt_level() -> Result<()> {
let td = TempDir::new()?;
let config_path = td.path().join("config.toml");
std::fs::write(
&config_path,
&format!(
"
[cache]
enabled = true
directory = '{}'
",
td.path().join("cache").display()
),
)?;
let mut cfg = Config::new();
cfg.cranelift_opt_level(OptLevel::None)
.cache_config_load(&config_path)?;
let engine = Engine::new(&cfg)?;
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 0);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 1);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
let mut cfg = Config::new();
cfg.cranelift_opt_level(OptLevel::Speed)
.cache_config_load(&config_path)?;
let engine = Engine::new(&cfg)?;
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 0);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 1);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
let mut cfg = Config::new();
cfg.cranelift_opt_level(OptLevel::SpeedAndSize)
.cache_config_load(&config_path)?;
let engine = Engine::new(&cfg)?;
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 0);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 1);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
// FIXME(#1523) need debuginfo on aarch64 before we run this test there
if !cfg!(target_arch = "aarch64") {
let mut cfg = Config::new();
cfg.debug_info(true).cache_config_load(&config_path)?;
let engine = Engine::new(&cfg)?;
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 0);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
Module::new(&engine, "(module (func))")?;
assert_eq!(engine.config().cache_config.cache_hits(), 1);
assert_eq!(engine.config().cache_config.cache_misses(), 1);
}
Ok(())
}
}