Implement shared host functions. (#2625)

* Implement defining host functions at the Config level.

This commit introduces defining host functions at the `Config` rather than with
`Func` tied to a `Store`.

The intention here is to enable a host to define all of the functions once
with a `Config` and then use a `Linker` (or directly with
`Store::get_host_func`) to use the functions when instantiating a module.

This should help improve the performance of use cases where a `Store` is
short-lived and redefining the functions at every module instantiation is a
noticeable performance hit.

This commit adds `add_to_config` to the code generation for Wasmtime's `Wasi`
type.

The new method adds the WASI functions to the given config as host functions.

This commit adds context functions to `Store`: `get` to get a context of a
particular type and `set` to set the context on the store.

For safety, `set` cannot replace an existing context value of the same type.

`Wasi::set_context` was added to set the WASI context for a `Store` when using
`Wasi::add_to_config`.

* Add `Config::define_host_func_async`.

* Make config "async" rather than store.

This commit moves the concept of "async-ness" to `Config` rather than `Store`.

Note: this is a breaking API change for anyone that's already adopted the new
async support in Wasmtime.

Now `Config::new_async` is used to create an "async" config and any `Store`
associated with that config is inherently "async".

This is needed for async shared host functions to have some sanity check during their
execution (async host functions, like "async" `Func`, need to be called with
the "async" variants).

* Update async function tests to smoke async shared host functions.

This commit updates the async function tests to also smoke the shared host
functions, plus `Func::wrap0_async`.

This also changes the "wrap async" method names on `Config` to
`wrap$N_host_func_async` to slightly better match what is on `Func`.

* Move the instance allocator into `Engine`.

This commit moves the instantiated instance allocator from `Config` into
`Engine`.

This makes certain settings in `Config` no longer order-dependent, which is how
`Config` should ideally be.

This also removes the confusing concept of the "default" instance allocator,
instead opting to construct the on-demand instance allocator when needed.

This does alter the semantics of the instance allocator as now each `Engine`
gets its own instance allocator rather than sharing a single one between all
engines created from a configuration.

* Make `Engine::new` return `Result`.

This is a breaking API change for anyone using `Engine::new`.

As creating the pooling instance allocator may fail (likely cause is not enough
memory for the provided limits), instead of panicking when creating an
`Engine`, `Engine::new` now returns a `Result`.

* Remove `Config::new_async`.

This commit removes `Config::new_async` in favor of treating "async support" as
any other setting on `Config`.

The setting is `Config::async_support`.

* Remove order dependency when defining async host functions in `Config`.

This commit removes the order dependency where async support must be enabled on
the `Config` prior to defining async host functions.

The check is now delayed to when an `Engine` is created from the config.

* Update WASI example to use shared `Wasi::add_to_config`.

This commit updates the WASI example to use `Wasi::add_to_config`.

As only a single store and instance are used in the example, it has no semantic
difference from the previous example, but the intention is to steer users
towards defining WASI on the config and only using `Wasi::add_to_linker` when
more explicit scoping of the WASI context is required.

crates/wasmtime/src/trampoline/func.rs

@@ -1,16 +1,15 @@
 //! Support for a calling of an imported function.
 
-use super::create_handle::create_handle;
-use crate::trampoline::StoreInstanceHandle;
-use crate::{FuncType, Store, Trap};
+use crate::{sig_registry::SignatureRegistry, Config, FuncType, Trap};
 use anyhow::Result;
 use std::any::Any;
 use std::cmp;
 use std::mem;
 use std::panic::{self, AssertUnwindSafe};
+use std::sync::Arc;
 use wasmtime_environ::entity::PrimaryMap;
 use wasmtime_environ::isa::TargetIsa;
-use wasmtime_environ::wasm::SignatureIndex;
+use wasmtime_environ::wasm::{DefinedFuncIndex, SignatureIndex};
 use wasmtime_environ::{ir, wasm, CompiledFunction, Module, ModuleType};
 use wasmtime_jit::trampoline::ir::{
     ExternalName, Function, InstBuilder, MemFlags, StackSlotData, StackSlotKind,
@@ -19,7 +18,10 @@ use wasmtime_jit::trampoline::{
     self, binemit, pretty_error, Context, FunctionBuilder, FunctionBuilderContext,
 };
 use wasmtime_jit::CodeMemory;
-use wasmtime_runtime::{InstanceHandle, VMContext, VMFunctionBody, VMTrampoline};
+use wasmtime_runtime::{
+    Imports, InstanceAllocationRequest, InstanceAllocator, InstanceHandle,
+    OnDemandInstanceAllocator, VMContext, VMFunctionBody, VMSharedSignatureIndex, VMTrampoline,
+};
 
 struct TrampolineState {
     func: Box<dyn Fn(*mut VMContext, *mut u128) -> Result<(), Trap>>,
@@ -203,19 +205,23 @@ fn make_trampoline(
         .expect("allocate_for_function")
 }
 
-pub fn create_handle_with_function(
+fn create_function_trampoline(
+    config: &Config,
     ft: &FuncType,
     func: Box<dyn Fn(*mut VMContext, *mut u128) -> Result<(), Trap>>,
-    store: &Store,
-) -> Result<(StoreInstanceHandle, VMTrampoline)> {
+) -> Result<(
+    Module,
+    PrimaryMap<DefinedFuncIndex, *mut [VMFunctionBody]>,
+    VMTrampoline,
+    TrampolineState,
+)> {
     // Note that we specifically enable reference types here in our ISA because
     // `Func::new` is intended to be infallible, but our signature may use
     // reference types which requires safepoints.
-    let isa = store.engine().config().target_isa_with_reference_types();
+    let isa = config.target_isa_with_reference_types();
 
     let pointer_type = isa.pointer_type();
     let sig = ft.get_wasmtime_signature(pointer_type);
-    let wft = ft.as_wasm_func_type();
 
     let mut fn_builder_ctx = FunctionBuilderContext::new();
     let mut module = Module::new();
@@ -226,10 +232,12 @@ pub fn create_handle_with_function(
     // and calls into `stub_fn`...
     let sig_id = SignatureIndex::from_u32(u32::max_value() - 1);
     module.types.push(ModuleType::Function(sig_id));
+
     let func_id = module.functions.push(sig_id);
     module
         .exports
         .insert(String::new(), wasm::EntityIndex::Function(func_id));
+
     let trampoline = make_trampoline(isa.as_ref(), &mut code_memory, &mut fn_builder_ctx, &sig);
     finished_functions.push(trampoline);
 
@@ -243,33 +251,51 @@ pub fn create_handle_with_function(
         &sig,
         mem::size_of::<u128>(),
     )?;
-    let shared_signature_id = store.signatures().borrow_mut().register(wft, trampoline);
 
-    // Next up we wrap everything up into an `InstanceHandle` by publishing our
-    // code memory (makes it executable) and ensuring all our various bits of
-    // state make it into the instance constructors.
     code_memory.publish(isa.as_ref());
+
     let trampoline_state = TrampolineState { func, code_memory };
-    create_handle(
-        module,
-        store,
-        finished_functions,
-        Box::new(trampoline_state),
-        &[],
-        Some(shared_signature_id),
-    )
-    .map(|instance| (instance, trampoline))
+
+    Ok((module, finished_functions, trampoline, trampoline_state))
 }
 
-pub unsafe fn create_handle_with_raw_function(
+pub fn create_function(
     ft: &FuncType,
-    func: *mut [VMFunctionBody],
-    trampoline: VMTrampoline,
-    store: &Store,
-    state: Box<dyn Any>,
-) -> Result<StoreInstanceHandle> {
-    let wft = ft.as_wasm_func_type();
+    func: Box<dyn Fn(*mut VMContext, *mut u128) -> Result<(), Trap>>,
+    config: &Config,
+    registry: Option<&mut SignatureRegistry>,
+) -> Result<(InstanceHandle, VMTrampoline)> {
+    let (module, finished_functions, trampoline, trampoline_state) =
+        create_function_trampoline(config, ft, func)?;
 
+    // If there is no signature registry, use the default signature index which is
+    // guaranteed to trap if there is ever an indirect call on the function (should not happen)
+    let shared_signature_id = registry
+        .map(|r| r.register(ft.as_wasm_func_type(), trampoline))
+        .unwrap_or(VMSharedSignatureIndex::default());
+
+    unsafe {
+        Ok((
+            OnDemandInstanceAllocator::new(None).allocate(InstanceAllocationRequest {
+                module: Arc::new(module),
+                finished_functions: &finished_functions,
+                imports: Imports::default(),
+                lookup_shared_signature: &|_| shared_signature_id,
+                host_state: Box::new(trampoline_state),
+                interrupts: std::ptr::null(),
+                externref_activations_table: std::ptr::null_mut(),
+                stack_map_registry: std::ptr::null_mut(),
+            })?,
+            trampoline,
+        ))
+    }
+}
+
+pub unsafe fn create_raw_function(
+    func: *mut [VMFunctionBody],
+    host_state: Box<dyn Any>,
+    shared_signature_id: VMSharedSignatureIndex,
+) -> Result<InstanceHandle> {
     let mut module = Module::new();
     let mut finished_functions = PrimaryMap::new();
 
@@ -280,14 +306,17 @@ pub unsafe fn create_handle_with_raw_function(
         .exports
         .insert(String::new(), wasm::EntityIndex::Function(func_id));
     finished_functions.push(func);
-    let shared_signature_id = store.signatures().borrow_mut().register(wft, trampoline);
 
-    create_handle(
-        module,
-        store,
-        finished_functions,
-        state,
-        &[],
-        Some(shared_signature_id),
+    Ok(
+        OnDemandInstanceAllocator::new(None).allocate(InstanceAllocationRequest {
+            module: Arc::new(module),
+            finished_functions: &finished_functions,
+            imports: Imports::default(),
+            lookup_shared_signature: &|_| shared_signature_id,
+            host_state,
+            interrupts: std::ptr::null(),
+            externref_activations_table: std::ptr::null_mut(),
+            stack_map_registry: std::ptr::null_mut(),
+        })?,
     )
 }