Async Calls

[adrien-zinger]

How do you know that all the asynchronous calls are associated to contracts that have gas ? This is similar to the problem we discussed for tx. You don't want to execute only contracts that do not have gas.
How do we handle contracts that don't have gas anymore with respect to asynchronous calls ?

In a near future 🚀 We want that a webassembly module could be able to wake up after a timeout. But how do we use metering? Which actors are engaged?

[yvan-sraka]

As I understand it, we should define https://doc.rust-lang.org/std/task/struct.Waker.html in our executor model to be able to handle async calls!

[damip]

I still don't really understand this xD would be cool to have some written specs + examples, or maybe even a minimal implementation

[damip]

Here we are talking about "async" in the sense of smart contracts (not rust).
It implies smart contracts being able to call a syscall such as:

send_message("target_address", AsyncMessage {
   delivery_slot: Slot(massa.get_current_slot().add_periods(2)),
   max_gas: 123,
   gas_price: 456,
   coins: 789,
   data: XXXXXXX,
});

this syscall will use message_send_gas_cost + message_conservation_gas_cost*(delivery_slot - massa.current_slot) from the current execution context. It will also spend max_gas*gas_price+coins from the sender.
It will then add this AsyncMessage to a list of messages to execute at the delivery_slot.
When executed, it will send "coins" to the target_address and call the method "message_event(context, data)" in "target_address" if it exists.

in target_address:

[yvan-sraka]

How much is this conceptually different from Rust async?

I would mean how do we manage that a SC will wait a computation from another SC? We will have to define something similar to an executor and wakers right?

[adrien-zinger]

As I understand this @yvan-sraka it'll never be implemented in this repository, it's another logic that must be implemented here https://github.com/massalabs/massa/blob/ebcb0e6bc1e4d48d035e47c6fb069dfc552eb65a/execution/src/vm.rs#L218-L219

[yvan-sraka]

massalabs/massa#1990