mempool/backend/rust-gbt/src/lib.rs

use napi::{
    bindgen_prelude::*,
    threadsafe_function::{ErrorStrategy, ThreadsafeFunction, ThreadsafeFunctionCallMode},
};
use napi_derive::napi;

use once_cell::sync::Lazy;
use std::collections::HashMap;
use std::sync::Mutex;

mod audit_transaction;
mod gbt;
mod thread_transaction;
mod utils;
use thread_transaction::ThreadTransaction;

/// Used for ThreadsafeFunction's queue size parameter
const UNBOUNDED_QUEUE: usize = 0;

static THREAD_TRANSACTIONS: Lazy<Mutex<HashMap<u32, ThreadTransaction>>> =
    Lazy::new(|| Mutex::new(HashMap::new()));

#[napi(ts_args_type = "mempoolBuffer: Uint8Array, callback: (result: GbtResult) => void")]
pub fn make(mempool_buffer: Uint8Array, callback: JsFunction) -> Result<()> {
    let mut map = HashMap::new();
    for tx in ThreadTransaction::batch_from_buffer(&mempool_buffer) {
        map.insert(tx.uid, tx);
    }

    let mut global_map = THREAD_TRANSACTIONS.lock().unwrap();
    *global_map = map;

    run_in_thread(callback)
}

#[napi(
    ts_args_type = "newTxs: Uint8Array, removeTxs: Uint8Array, callback: (result: GbtResult) => void"
)]
pub fn update(new_txs: Uint8Array, remove_txs: Uint8Array, callback: JsFunction) -> Result<()> {
    let mut map = THREAD_TRANSACTIONS.lock().unwrap();
    for tx in ThreadTransaction::batch_from_buffer(&new_txs) {
        map.insert(tx.uid, tx);
    }
    for txid in &utils::txids_from_buffer(&remove_txs) {
        map.remove(txid);
    }
    drop(map);

    run_in_thread(callback)
}

/// The result from calling the gbt function.
///
/// This tuple contains the following:
///   blocks: A 2D Vector of transaction IDs (u32), the inner Vecs each represent a block.
/// clusters: A 2D Vector of transaction IDs representing clusters of dependent mempool transactions
///    rates: A Vector of tuples containing transaction IDs (u32) and effective fee per vsize (f64)
#[napi(constructor)]
pub struct GbtResult {
    pub blocks: Vec<Vec<u32>>,
    pub clusters: Vec<Vec<u32>>,
    pub rates: Vec<Vec<f64>>, // Tuples not supported. u32 fits inside f64
}

fn run_in_thread(callback: JsFunction) -> Result<()> {
    let thread_safe_callback: ThreadsafeFunction<GbtResult, ErrorStrategy::Fatal> =
        callback.create_threadsafe_function(UNBOUNDED_QUEUE, |ctx| Ok(vec![ctx.value]))?;

    let handle = std::thread::spawn(move || {
        let mut map = THREAD_TRANSACTIONS
            .lock()
            .map_err(|_| napi::Error::from_reason("THREAD_TRANSACTIONS Mutex poisoned"))?;
        let result = gbt::gbt(&mut map).ok_or_else(|| napi::Error::from_reason("gbt failed"))?;

        // Note: A call mode of Blocking does not mean it will block, but rather it tells
        // the N-API what to do in the event of a full queue.
        // The queue will never be full, so Blocking is fine.
        thread_safe_callback.call(result, ThreadsafeFunctionCallMode::Blocking);
        Ok(())
    });

    handle
        .join()
        .map_err(|_| napi::Error::from_reason("thread panicked"))?
}