How can I make an asynchronous interaction between two contracts?

Question

How can I make an asynchronous interaction between two contracts? I have contract A and contract B.

is it possible to realize the interaction between A and B through callback?

Does this answer your question? Can I make 'wait n seconds' statement in solidity function? — Ismael, Dec 25 '20 at 2:05

goodvibration · Accepted Answer · 2020-12-24 16:55:54Z

1

The 2nd bullet is not possible strictly from on-chain.

The asynchronous part of your system can only be an off-chain service which sends the data.

The rest of the process, as depicted in the 1st and 3rd bullets, will be synchronous of course.

answered Dec 24 '20 at 16:55

goodvibration

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can you give me an example of how B returns data to A? – Mario Roma Dec 24 '20 at 17:02
@MarioRoma: When "contract A calls contract B" (your 1st bullet), immediately "contract B returns the data to A" (your 3rd bullet). By immediately, I mean within the same transaction. – goodvibration Dec 24 '20 at 17:15
the only way to make the interaction asynchronous is to use events? When contract B has obtained the data it emits an event and A makes a transaction to B to retrieve the data.Is it right? – Mario Roma Dec 24 '20 at 17:23
@MarioRoma: No, that's wrong. Events are used only for recording data on the blockchain. Contracts can only emit events, they cannot read them. Events can be used only in an off-chain script/app/service. Please read the answer again. You cannot achieve an asynchronous process strictly in the on-chain. The asynchronous part of your system must be implemented in the off-chain. – goodvibration Dec 24 '20 at 17:26
I meant that a node receives the event it subscribed to and calls contract A. contract A calls contract B and retrieves the data. – Mario Roma Dec 24 '20 at 17:29

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