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Add wasmtime-specific C APIs for tables (#1654)
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This commit adds a suite of `wasmtime_funcref_table_*` APIs which mirror
the standard APIs but have a few differences:

* More errors are returned. For example error messages are communicated
  through `wasmtime_error_t` and out-of-bounds vs load of null can be
  differentiated in the `get` API.

* APIs take `wasm_func_t` instead of `wasm_ref_t`. Given the recent
  decision to remove subtyping from the anyref proposal it's not clear
  how the C API for tables will be affected, so for now these APIs are
  all specialized to only funcref tables.

* Growth now allows access to the previous size of the table, if
  desired, which mirrors the `table.grow` instruction.

This was originally motivated by bytecodealliance/wasmtime-go#5 where
the current APIs we have for working with tables don't quite work. We
don't have a great way to take an anyref constructed from a `Func` and
get the `Func` back out, so for now this sidesteps those concerns while
we sort out the anyref story.

It's intended that once the anyref story has settled and the official C
API has updated we'll likely delete these wasmtime-specific APIs or
implement them as trivial wrappers around the official ones.
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alexcrichton authored May 13, 2020
1 parent fb0b9e3 commit 1247f2b
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Showing 3 changed files with 123 additions and 18 deletions.
26 changes: 26 additions & 0 deletions crates/c-api/include/wasmtime.h
Original file line number Diff line number Diff line change
Expand Up @@ -254,6 +254,32 @@ WASM_API_EXTERN own wasmtime_error_t *wasmtime_module_validate(
const wasm_byte_vec_t *binary
);


// Similar to `wasm_table_*`, except these explicitly operate on funcref tables
// and work with `wasm_func_t` values instead of `wasm_ref_t`.
WASM_API_EXTERN own wasmtime_error_t *wasmtime_funcref_table_new(
wasm_store_t *store,
const wasm_tabletype_t *element_ty,
wasm_func_t *init,
own wasm_table_t **table
);
WASM_API_EXTERN bool wasmtime_funcref_table_get(
const wasm_table_t *table,
wasm_table_size_t index,
own wasm_func_t **func
);
WASM_API_EXTERN own wasmtime_error_t *wasmtime_funcref_table_set(
wasm_table_t *table,
wasm_table_size_t index,
const wasm_func_t *value
);
WASM_API_EXTERN wasmtime_error_t *wasmtime_funcref_table_grow(
wasm_table_t *table,
wasm_table_size_t delta,
const wasm_func_t *init,
wasm_table_size_t *prev_size
);

#undef own

#ifdef __cplusplus
Expand Down
18 changes: 12 additions & 6 deletions crates/c-api/src/func.rs
Original file line number Diff line number Diff line change
Expand Up @@ -63,7 +63,7 @@ impl wasm_func_t {
}
}

fn func(&self) -> &HostRef<Func> {
pub(crate) fn func(&self) -> &HostRef<Func> {
match &self.ext.which {
ExternHost::Func(f) => f,
_ => unsafe { std::hint::unreachable_unchecked() },
Expand All @@ -75,6 +75,16 @@ impl wasm_func_t {
}
}

impl From<HostRef<Func>> for wasm_func_t {
fn from(func: HostRef<Func>) -> wasm_func_t {
wasm_func_t {
ext: wasm_extern_t {
which: ExternHost::Func(func),
},
}
}
}

fn create_function(
store: &wasm_store_t,
ty: &wasm_functype_t,
Expand All @@ -97,11 +107,7 @@ fn create_function(
}
Ok(())
});
Box::new(wasm_func_t {
ext: wasm_extern_t {
which: ExternHost::Func(HostRef::new(func)),
},
})
Box::new(HostRef::new(func).into())
}

#[no_mangle]
Expand Down
97 changes: 85 additions & 12 deletions crates/c-api/src/table.rs
Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
use crate::wasm_ref_t;
use crate::{handle_result, wasm_func_t, wasm_ref_t, wasmtime_error_t};
use crate::{wasm_extern_t, wasm_store_t, wasm_tabletype_t, ExternHost};
use std::ptr;
use wasmtime::{AnyRef, HostRef, Table, Val};
Expand Down Expand Up @@ -34,15 +34,14 @@ impl wasm_table_t {
}

#[no_mangle]
pub unsafe extern "C" fn wasm_table_new(
pub extern "C" fn wasm_table_new(
store: &wasm_store_t,
tt: &wasm_tabletype_t,
init: *mut wasm_ref_t,
init: Option<Box<wasm_ref_t>>,
) -> Option<Box<wasm_table_t>> {
let init: Val = if !init.is_null() {
Box::from_raw(init).r.into()
} else {
Val::AnyRef(AnyRef::Null)
let init: Val = match init {
Some(init) => init.r.into(),
None => Val::AnyRef(AnyRef::Null),
};
let table = Table::new(&store.store.borrow(), tt.ty().ty.clone(), init).ok()?;
Some(Box::new(wasm_table_t {
Expand All @@ -52,23 +51,66 @@ pub unsafe extern "C" fn wasm_table_new(
}))
}

#[no_mangle]
pub extern "C" fn wasmtime_funcref_table_new(
store: &wasm_store_t,
tt: &wasm_tabletype_t,
init: Option<&wasm_func_t>,
out: &mut *mut wasm_table_t,
) -> Option<Box<wasmtime_error_t>> {
let init: Val = match init {
Some(val) => Val::FuncRef(val.func().borrow().clone()),
None => Val::AnyRef(AnyRef::Null),
};
handle_result(
Table::new(&store.store.borrow(), tt.ty().ty.clone(), init),
|table| {
*out = Box::into_raw(Box::new(wasm_table_t {
ext: wasm_extern_t {
which: ExternHost::Table(HostRef::new(table)),
},
}));
println!("ret at {:?}", *out);
},
)
}

#[no_mangle]
pub extern "C" fn wasm_table_type(t: &wasm_table_t) -> Box<wasm_tabletype_t> {
let ty = t.table().borrow().ty();
Box::new(wasm_tabletype_t::new(ty))
}

#[no_mangle]
pub unsafe extern "C" fn wasm_table_get(
t: &wasm_table_t,
index: wasm_table_size_t,
) -> *mut wasm_ref_t {
pub extern "C" fn wasm_table_get(t: &wasm_table_t, index: wasm_table_size_t) -> *mut wasm_ref_t {
match t.table().borrow().get(index) {
Some(val) => into_funcref(val),
None => into_funcref(Val::AnyRef(AnyRef::Null)),
}
}

#[no_mangle]
pub extern "C" fn wasmtime_funcref_table_get(
t: &wasm_table_t,
index: wasm_table_size_t,
ptr: &mut *mut wasm_func_t,
) -> bool {
println!("get {:p} at {}", t, index);
match t.table().borrow().get(index) {
Some(val) => {
*ptr = match val {
// TODO: what do do about creating new `HostRef` handles here?
Val::FuncRef(f) => Box::into_raw(Box::new(HostRef::new(f).into())),
Val::AnyRef(AnyRef::Null) => ptr::null_mut(),
_ => return false,
};
}

_ => return false,
}
true
}

#[no_mangle]
pub unsafe extern "C" fn wasm_table_set(
t: &wasm_table_t,
Expand All @@ -79,7 +121,20 @@ pub unsafe extern "C" fn wasm_table_set(
t.table().borrow().set(index, val).is_ok()
}

unsafe fn into_funcref(val: Val) -> *mut wasm_ref_t {
#[no_mangle]
pub extern "C" fn wasmtime_funcref_table_set(
t: &wasm_table_t,
index: wasm_table_size_t,
val: Option<&wasm_func_t>,
) -> Option<Box<wasmtime_error_t>> {
let val = match val {
Some(val) => Val::FuncRef(val.func().borrow().clone()),
None => Val::AnyRef(AnyRef::Null),
};
handle_result(t.table().borrow().set(index, val), |()| {})
}

fn into_funcref(val: Val) -> *mut wasm_ref_t {
if let Val::AnyRef(AnyRef::Null) = val {
return ptr::null_mut();
}
Expand Down Expand Up @@ -114,6 +169,24 @@ pub unsafe extern "C" fn wasm_table_grow(
t.table().borrow().grow(delta, init).is_ok()
}

#[no_mangle]
pub extern "C" fn wasmtime_funcref_table_grow(
t: &wasm_table_t,
delta: wasm_table_size_t,
init: Option<&wasm_func_t>,
prev_size: Option<&mut wasm_table_size_t>,
) -> Option<Box<wasmtime_error_t>> {
let val = match init {
Some(val) => Val::FuncRef(val.func().borrow().clone()),
None => Val::AnyRef(AnyRef::Null),
};
handle_result(t.table().borrow().grow(delta, val), |prev| {
if let Some(ptr) = prev_size {
*ptr = prev;
}
})
}

#[no_mangle]
pub extern "C" fn wasm_table_as_extern(t: &wasm_table_t) -> &wasm_extern_t {
&t.ext
Expand Down

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