Is it possible to have an async heartbeat function?

Developers
1

The use case is that I would like to call async functions from heartbeat.

It is possible to change update (and I presume query) to async and thereby allow async functions to be made from them. Condvar wait not supported

However the heartbeat function appears to be sync. When I try to add async to heartbeat function definition, I get the following error:

The invocation to the wallet call forward method failed with the error: An error happened during the call: 5: Wasm module of canister sbzkb-zqaaa-aaaaa-aaaiq-cai is not valid: Wasm module has an invalid function signature. Expected return type for ā€˜canister_heartbeatā€™, got [I32]

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2

Rust or Motoko?

(This question is too short for the forum)

3

In rust.

(The answer is too short for forum)

4

Just based on your error message, is your heartbeat function returning an i32? Try it without a return type.

5

The heart beat function is not returning a i32

if I have the function without async,

#[export_name = ā€œcanister_heartbeatā€]
fn heartbeat_fn () {
ic_cdk::print(ā€œniceā€);
}

works fine.

However with async, not so.

#[export_name = ā€œcanister_heartbeatā€]
async fn heartbeat_fn () {
ic_cdk::print(ā€œniceā€);
}
ā€¦
Installing code for canister dfx_hello, with canister_id tzq7c-xqaaa-aaaaa-aaamq-cai
The invocation to the wallet call forward method failed with the error: An error happened during the call: 5: Wasm module of canister tzq7c-xqaaa-aaaaa-aaamq-cai is not valid: Wasm module has an invalid function signature. Expected return type for ā€˜canister_heartbeatā€™, got [I32].

1 Like
6

Did you ever get this sorted? I am trying to get a canister_heartbeat function working right now and Iā€™m hoping to do cross canister calls from it, I hope this works

7

I was not able to. It would be very useful to have this heartbeat in an async context.

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8

You should at least be able to do ic_cdk::spawn

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9

At least in Motoko, the heartbeat system function can definitely make and await on calls to other canisters.

See the docs:

As an async function, Alarmā€™s hearbeat function is free to call other asynchronous functions (the inner call to ring() above is an example), as well as shared functions of other c

That would be strange if it worked in Motoko but not in Rustā€¦

1 Like
10 
#[heartbeat]
fn tick() {
  ic_cdk::block_on(async_function());
}

or

#[heartbeat]
fn tick() {
  ic_cdk::block_on(async {
    async_function_1().await;
    async_function_2().await;
  });
}
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11

This definitely works, but you want to use ic_cdk::spawn now as ic_cdk::block_on was a misnomer and is deprecated.

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