pub struct Engine { /* private fields */ }Expand description
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.
Implementations§
source§impl Engine
impl Engine
sourcepub fn new(config: &Config) -> Result<Engine>
pub fn new(config: &Config) -> Result<Engine>
Creates a new Engine with the specified compilation and
configuration settings.
§Errors
This method can fail if the config is invalid or some
configurations are incompatible.
For example, feature reference_types will need to set
the compiler setting enable_safepoints and unwind_info
to true, but explicitly disable these two compiler settings
will cause errors.
sourcepub fn weak(&self) -> EngineWeak
pub fn weak(&self) -> EngineWeak
Take a weak reference to this engine.
sourcepub fn same(a: &Engine, b: &Engine) -> bool
pub fn same(a: &Engine, b: &Engine) -> bool
Returns whether the engine a and b refer to the same configuration.
sourcepub fn detect_precompiled(&self, bytes: &[u8]) -> Option<Precompiled>
pub fn detect_precompiled(&self, bytes: &[u8]) -> Option<Precompiled>
Detects whether the bytes provided are a precompiled object produced by Wasmtime.
This function will inspect the header of bytes to determine if it
looks like a precompiled core wasm module or a precompiled component.
This does not validate the full structure or guarantee that
deserialization will succeed, instead it helps higher-levels of the
stack make a decision about what to do next when presented with the
bytes as an input module.
If the bytes looks like a precompiled object previously produced by
Module::serialize,
Component::serialize,
Engine::precompile_module, or Engine::precompile_component, then
this will return Some(...) indicating so. Otherwise None is
returned.
sourcepub fn detect_precompiled_file(
&self,
path: impl AsRef<Path>
) -> Result<Option<Precompiled>>
pub fn detect_precompiled_file( &self, path: impl AsRef<Path> ) -> Result<Option<Precompiled>>
Like Engine::detect_precompiled, but performs the detection on a file.
source§impl Engine
impl Engine
sourcepub fn precompile_module(&self, bytes: &[u8]) -> Result<Vec<u8>>
Available on crate features cranelift or winch only.
pub fn precompile_module(&self, bytes: &[u8]) -> Result<Vec<u8>>
cranelift or winch only.Ahead-of-time (AOT) compiles a WebAssembly module.
The bytes provided must be in one of two formats:
- A binary-encoded WebAssembly module. This is always supported.
- A text-encoded instance of the WebAssembly text format.
This is only supported when the
watfeature of this crate is enabled. If this is supplied then the text format will be parsed before validation. Note that thewatfeature 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 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 from the output of this method.
sourcepub fn precompile_component(&self, bytes: &[u8]) -> Result<Vec<u8>>
Available on (crate features cranelift or winch) and crate feature component-model only.
pub fn precompile_component(&self, bytes: &[u8]) -> Result<Vec<u8>>
cranelift or winch) and crate feature component-model only.Same as Engine::precompile_module except for a
Component
source§impl Engine
impl Engine
sourcepub fn tls_eager_initialize()
Available on crate feature runtime only.
pub fn tls_eager_initialize()
runtime only.Eagerly initialize thread-local functionality shared by all Engines.
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.
sourcepub fn increment_epoch(&self)
Available on crate feature runtime only.
pub fn increment_epoch(&self)
runtime only.Increments the epoch.
When using epoch-based interruption, currently-executing Wasm
code within this engine will trap or yield “soon” when the
epoch deadline is reached or exceeded. (The configuration, and
the deadline, are set on the Store.) The intent of the
design is for this method to be called by the embedder at some
regular cadence, for example by a thread that wakes up at some
interval, or by a signal handler.
See Config::epoch_interruption
for an introduction to epoch-based interruption and pointers
to the other relevant methods.
When performing increment_epoch in a separate thread, consider using
Engine::weak to hold an EngineWeak and
performing EngineWeak::upgrade on each
tick, so that the epoch ticking thread does not keep an Engine alive
longer than any of its consumers.
§Signal Safety
This method is signal-safe: it does not make any syscalls, and performs only an atomic increment to the epoch value in memory.
sourcepub fn precompile_compatibility_hash(&self) -> impl Hash + '_
Available on crate features runtime and cranelift only.
pub fn precompile_compatibility_hash(&self) -> impl Hash + '_
runtime and cranelift only.Returns a std::hash::Hash that can be used to check precompiled WebAssembly compatibility.
The outputs of Engine::precompile_module and Engine::precompile_component
are compatible with a different Engine instance only if the two engines use
compatible Configs. If this Hash matches between two Engines then binaries
from one are guaranteed to deserialize in the other.