1. You can use the lazy_static crate to create a global thread-local hasher in risingwave.

2. Here's an example of how you can achieve this:

use lazy_static::lazy_static;
use std::cell::RefCell;
use sha1::{Sha1, Digest};

lazy_static! {
    static ref HASHER: RefCell<Sha1> = RefCell::new(Sha1::new());
}

pub fn sha1(data: &[u8]) -> Result<Box<[u8]>> {
    let mut hasher = HASHER.borrow_mut();
    // Use the hasher for processing data
    let result = hasher.result();
    hasher.reset(); // Reset the hasher for the next function call
    Ok(result.into_boxed_slice())
}