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Refactor code to remove async move closure which may result in double… #1256

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Refactor code to remove async move closure which may result in double… #1256

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42 changes: 20 additions & 22 deletions juniper/src/types/async_await.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -258,31 +258,29 @@ where
let is_non_null = meta_field.field_type.is_non_null();

let response_name = response_name.to_string();
async_values.push_back(AsyncValueFuture::Field(async move {
// TODO: implement custom future type instead of
// two-level boxing.
Comment on lines -262 to -263
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I don't see any boxing at all.. AsyncValueFuture is generic so this comment looks outdated.

let res = instance
.resolve_field_async(info, f.name.item, &args, &sub_exec)
.await;

let value = match res {
Ok(Value::Null) if is_non_null => None,
Ok(v) => Some(v),
Err(e) => {
sub_exec.push_error_at(e, pos);

if is_non_null {
None
} else {
Some(Value::null())
}
let res = instance
.resolve_field_async(info, f.name.item, &args, &sub_exec)
.await;
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It looks like this .await breaks concurrency. The await now happens directly within the for loop body, so the future will pause at this point before processing the next select. The intention of async_values is that the loop should produce all the futures synchronously up front, then after this loop there is another while loop at the bottom of the function which polls the FuturesOrdered so that all its contained futures may progress simultaneously.


let value = match res {
Ok(Value::Null) if is_non_null => None,
Ok(v) => Some(v),
Err(e) => {
sub_exec.push_error_at(e, pos);
if is_non_null {
None
} else {
Some(Value::null())
}
};
AsyncValue::Field(AsyncField {
}
};

async_values.push_back(AsyncValueFuture::Field(future::ready(AsyncValue::Field(
AsyncField {
name: response_name,
value,
})
}));
},
))));
}

Selection::FragmentSpread(Spanning {
Expand Down