futures::join! two Futures from api

[lx38]

Trying to understand how to make parallel calls , just like I can do via polkadotjs/api via Promises.all()

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>>{

    let api = ClientBuilder::new()
        .set_url("wss://rpc.polkadot.io:443")
        .build()
        .await?
        .to_runtime_api::<polkadot::api::RuntimeApi<DefaultConfig, SubstrateExtrinsicParams<DefaultConfig>>>();


    let addr = AccountId32::from_str("13Ybj8CPEArUee78DxUAP9yX3ABmFNVQME1ZH4w8HVncHGzc").unwrap();

    let controller = api.storage().staking().bonded(&addr, None);
    let ledger = api.storage().staking().ledger(&addr, None);

    let (a, b) = join!(controller, ledger);

    Ok(())
}

What I get is the following:

22 |     let controller = api.storage().staking().bonded(&addr, None);
   |                      ^^^^^^^^^^^^^^^^^^^^^^^                    - temporary value is freed at the end of this statement
   |                      |
   |                      creates a temporary which is freed while still in use
...
25 |     let (a, b) = join!(controller, ledger);
   |                        ---------- borrow later used here

I can extract staking and ledger as variables, but maybe I do something wrong? probably I do not understand the concept.

[lx38]

PS. extracting vars does not help too much. I doing lotsa requests for multiple accounts and Rust code operates 2 times slower than equivalent Nodejs code..

[jsdw]

Your above example doesn't work becuase the bonded()/ledger() calls are both async functions that borrow self (eg borrow the thing returned from staking(). Extracting that variable out so that it lives long enough makes it compile:

use subxt::sp_core::crypto::AccountId32;
use futures::join;
use std::str::FromStr;
use subxt::{
    PolkadotExtrinsicParams,
    ClientBuilder,
    DefaultConfig,
};

#[subxt::subxt(runtime_metadata_path = "../artifacts/polkadot_metadata.scale")]
pub mod polkadot {}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>>{

    let api = ClientBuilder::new()
        .set_url("wss://rpc.polkadot.io:443")
        .build()
        .await?
        .to_runtime_api::<polkadot::RuntimeApi<DefaultConfig, PolkadotExtrinsicParams<DefaultConfig>>>();


    let addr = AccountId32::from_str("13Ybj8CPEArUee78DxUAP9yX3ABmFNVQME1ZH4w8HVncHGzc").unwrap();

    let staking = api.storage().staking();
    let controller = staking.bonded(&addr, None);
    let ledger = staking.ledger(&addr, None);

    let (a, b) = join!(controller, ledger);

    Ok(())
}

We might be able to improve the ergonomics here by, instead of having async fns, being a bit more explicit and generating code like:

fn bonded(&self, ...) -> impl Future<Item=Foo> + 'a {
    let client = &self.client;
    async move {
        // take ownership of client, not all of self in the future, so that we dont rely on borrow,
        // and put rest of generated logic in here.
    }
}

[jsdw]

The above PR should make what you originally tried to do work (although note that you should use PolkadotExtrinsicParams, not SubstrateExtrinsicParams really if you're connecting to a polkadot node (for accessing storage items it makes no difference, but you'd run into issues trying to submit transactions)

[lx38]

@jsdw thanks for clarification/example on usage. I can use features w/o any issues now. Thanks for spotting incorrect struct usage. This was taken from README.md, where it uses SubstrateExtrinsicParams instead of PolkadotExtrinsicParams, so I think you shall amend it too..

[jsdw]

Ah you're right; I'll tweak the README to fix that error :)