Function promise_yield_create

pub fn promise_yield_create(
    function_name: &str,
    arguments: &[u8],
    gas: Gas,
    weight: GasWeight,
    register_id: u64,
) -> PromiseIndex

Creates a promise that will execute a method on the current account with given arguments. Writes a resumption token (data id) to the specified register. The callback method will execute after promise_yield_resume is called with the data id OR enough blocks have passed. The timeout length is specified as a protocol-level parameter yield_timeout_length_in_blocks = 200.

The callback method will execute with a single promise input. Input will either be a payload provided by the user when calling promise_yield_resume, or a PromiseError in case of timeout.

Resumption tokens are specific to the local account; promise_yield_resume must be called from a method of the same contract.

Examples

use near_sdk::env::{promise_yield_create, promise_yield_resume, read_register};
use near_sdk::serde_json;
use near_sdk::{Gas, GasWeight, CryptoHash};

let DATA_ID_REGISTER = 0;
// Create yield promise
let promise = promise_yield_create(
    "increment",
    // passed as arguments
    serde_json::json!({
        "value": 5        
    }).to_string().into_bytes().as_slice(),
    Gas::from_tgas(10),
    GasWeight(0),
    DATA_ID_REGISTER
);

// Retrieve `data_id` for further resume
let data_id: CryptoHash = read_register(DATA_ID_REGISTER)
    .expect("read_register failed")
    .try_into()
    .expect("conversion to CryptoHash failed");

// Resume execution using previously retrieved `data_id`
promise_yield_resume(
    &data_id,
    // passed as callback_result
    serde_json::json!({
        "key": "value",
        "description": "some text"
    }).to_string().into_bytes().as_slice()
);

More low-level info here: near_vm_runner::logic::VMLogic::promise_yield_create See example of usage here and here