Use a class to hold state for Rust GbtGenerator

backend/rust-gbt/index.d.ts

@@ -3,8 +3,11 @@
 
 /* auto-generated by NAPI-RS */
 
-export function make(mempoolBuffer: Uint8Array): Promise<GbtResult>
-export function update(newTxs: Uint8Array, removeTxs: Uint8Array): Promise<GbtResult>
+export class GbtGenerator {
+  constructor()
+  make(mempoolBuffer: Uint8Array): Promise<GbtResult>
+  update(newTxs: Uint8Array, removeTxs: Uint8Array): Promise<GbtResult>
+}
 /**
  * The result from calling the gbt function.
  *

backend/rust-gbt/index.js

@@ -252,8 +252,7 @@ if (!nativeBinding) {
   throw new Error(`Failed to load native binding`)
 }
 
-const { make, update, GbtResult } = nativeBinding
+const { GbtGenerator, GbtResult } = nativeBinding
 
-module.exports.make = make
-module.exports.update = update
+module.exports.GbtGenerator = GbtGenerator
 module.exports.GbtResult = GbtResult

backend/rust-gbt/src/gbt.rs

@@ -4,9 +4,7 @@ use std::{
     collections::{HashMap, HashSet, VecDeque},
 };
 
-use crate::{
-    audit_transaction::AuditTransaction, thread_transaction::ThreadTransaction, GbtResult,
-};
+use crate::{audit_transaction::AuditTransaction, GbtResult, ThreadTransactionsMap};
 
 const BLOCK_WEIGHT_UNITS: u32 = 4_000_000;
 const BLOCK_SIGOPS: u32 = 80_000;
@@ -43,7 +41,7 @@ impl Ord for TxPriority {
 * (see BlockAssembler in https://github.com/bitcoin/bitcoin/blob/master/src/node/miner.cpp)
 * Ported from https://github.com/mempool/mempool/blob/master/backend/src/api/tx-selection-worker.ts
 */
-pub fn gbt(mempool: &mut HashMap<u32, ThreadTransaction>) -> Option<GbtResult> {
+pub fn gbt(mempool: &mut ThreadTransactionsMap) -> Option<GbtResult> {
     let mut audit_pool: HashMap<u32, AuditTransaction> = HashMap::new();
     let mut mempool_array: VecDeque<u32> = VecDeque::new();
     let mut clusters: Vec<Vec<u32>> = Vec::new();

backend/rust-gbt/src/lib.rs

@@ -1,9 +1,9 @@
 use napi::bindgen_prelude::*;
 use napi_derive::napi;
 
-use once_cell::sync::Lazy;
 use std::collections::HashMap;
-use std::sync::Mutex;
+use std::sync::{Arc, Mutex};
+use utils::U32HasherState;
 
 mod audit_transaction;
 mod gbt;
@@ -11,41 +11,48 @@ mod thread_transaction;
 mod utils;
 use thread_transaction::ThreadTransaction;
 
-static THREAD_TRANSACTIONS: Lazy<Mutex<HashMap<u32, ThreadTransaction>>> =
-    Lazy::new(|| Mutex::new(HashMap::new()));
+type ThreadTransactionsMap = HashMap<u32, ThreadTransaction, U32HasherState>;
 
-#[napi(ts_args_type = "mempoolBuffer: Uint8Array")]
-pub async fn make(mempool_buffer: Uint8Array) -> Result<GbtResult> {
-    let mut map = HashMap::new();
+#[napi]
+pub struct GbtGenerator {
+    thread_transactions: Arc<Mutex<ThreadTransactionsMap>>,
+}
+
+#[napi]
+impl GbtGenerator {
+    #[napi(constructor)]
+    #[allow(clippy::new_without_default)]
+    pub fn new() -> Self {
+        Self {
+            thread_transactions: Arc::new(Mutex::new(HashMap::with_capacity_and_hasher(
+                2048,
+                U32HasherState,
+            ))),
+        }
+    }
+
+    #[napi]
+    pub async fn make(&self, mempool_buffer: Uint8Array) -> Result<GbtResult> {
+        run_task(Arc::clone(&self.thread_transactions), move |map| {
             for tx in ThreadTransaction::batch_from_buffer(&mempool_buffer) {
                 map.insert(tx.uid, tx);
             }
-
-    {
-        let mut global_map = THREAD_TRANSACTIONS
-            .lock()
-            .map_err(|_| napi::Error::from_reason("THREAD_TRANSACTIONS Mutex poisoned"))?;
-        *global_map = map;
+        })
+        .await
     }
 
-    run_in_thread().await
-}
-
-#[napi(ts_args_type = "newTxs: Uint8Array, removeTxs: Uint8Array")]
-pub async fn update(new_txs: Uint8Array, remove_txs: Uint8Array) -> Result<GbtResult> {
-    {
-        let mut map = THREAD_TRANSACTIONS
-            .lock()
-            .map_err(|_| napi::Error::from_reason("THREAD_TRANSACTIONS Mutex poisoned"))?;
+    #[napi]
+    pub async fn update(&self, new_txs: Uint8Array, remove_txs: Uint8Array) -> Result<GbtResult> {
+        run_task(Arc::clone(&self.thread_transactions), move |map| {
             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);
             }
+        })
+        .await
     }
-
-    run_in_thread().await
 }
 
 /// The result from calling the gbt function.
@@ -61,11 +68,27 @@ pub struct GbtResult {
     pub rates: Vec<Vec<f64>>, // Tuples not supported. u32 fits inside f64
 }
 
-async fn run_in_thread() -> Result<GbtResult> {
+/// All on another thread, this runs an arbitrary task in between
+/// taking the lock and running gbt.
+///
+/// Rather than filling / updating the HashMap on the main thread,
+/// this allows for HashMap modifying tasks to be run before running and returning gbt results.
+///
+/// `thread_transactions` is a cloned Arc of the Mutex for the HashMap state.
+/// `callback` is a `'static + Send` `FnOnce` closure/function that takes a mutable reference
+/// to the HashMap as the only argument. (A move closure is recommended to meet the bounds)
+async fn run_task<F>(
+    thread_transactions: Arc<Mutex<ThreadTransactionsMap>>,
+    callback: F,
+) -> Result<GbtResult>
+where
+    F: FnOnce(&mut ThreadTransactionsMap) + Send + 'static,
+{
     let handle = napi::tokio::task::spawn_blocking(move || {
-        let mut map = THREAD_TRANSACTIONS
+        let mut map = thread_transactions
             .lock()
             .map_err(|_| napi::Error::from_reason("THREAD_TRANSACTIONS Mutex poisoned"))?;
+        callback(&mut map);
         gbt::gbt(&mut map).ok_or_else(|| napi::Error::from_reason("gbt failed"))
     });
 

backend/rust-gbt/src/utils.rs

@@ -1,5 +1,8 @@
 use bytes::buf::Buf;
-use std::io::Cursor;
+use std::{
+    hash::{BuildHasher, Hasher},
+    io::Cursor,
+};
 
 pub fn txids_from_buffer(buffer: &[u8]) -> Vec<u32> {
     let mut txids: Vec<u32> = Vec::new();
@@ -11,3 +14,56 @@ pub fn txids_from_buffer(buffer: &[u8]) -> Vec<u32> {
 
     txids
 }
+
+pub struct U32HasherState;
+
+impl BuildHasher for U32HasherState {
+    type Hasher = U32Hasher;
+
+    fn build_hasher(&self) -> Self::Hasher {
+        U32Hasher(0)
+    }
+}
+
+pub struct U32Hasher(u32);
+
+impl Hasher for U32Hasher {
+    fn finish(&self) -> u64 {
+        // Safety: Two u32s next to each other will make a u64
+        unsafe { core::mem::transmute::<(u32, u32), u64>((self.0, 0_u32)) }
+    }
+
+    fn write(&mut self, bytes: &[u8]) {
+        // Assert in debug builds (testing too) that only 4 byte keys (u32, i32, f32, etc.) run
+        debug_assert!(bytes.len() == 4);
+        // Safety: We know that the size of the key is at least 4 bytes
+        self.0 = unsafe { *bytes.as_ptr().cast::<u32>() };
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashMap;
+
+    use super::U32HasherState;
+
+    #[test]
+    fn test_me() {
+        let mut hm: HashMap<u32, String, U32HasherState> = HashMap::with_hasher(U32HasherState);
+
+        hm.insert(0, String::from("0"));
+        hm.insert(42, String::from("42"));
+        hm.insert(256, String::from("256"));
+        hm.insert(u32::MAX, String::from("MAX"));
+        hm.insert(u32::MAX >> 2, String::from("MAX >> 2"));
+
+        assert_eq!(hm.get(&0), Some(&String::from("0")));
+        assert_eq!(hm.get(&42), Some(&String::from("42")));
+        assert_eq!(hm.get(&256), Some(&String::from("256")));
+        assert_eq!(hm.get(&u32::MAX), Some(&String::from("MAX")));
+        assert_eq!(hm.get(&(u32::MAX >> 2)), Some(&String::from("MAX >> 2")));
+        assert_eq!(hm.get(&(u32::MAX >> 4)), None);
+        assert_eq!(hm.get(&3), None);
+        assert_eq!(hm.get(&43), None);
+    }
+}

backend/src/api/mempool-blocks.ts

@@ -1,4 +1,4 @@
-import * as napiAddon from '../../rust-gbt';
+import { GbtGenerator } from '../../rust-gbt';
 import logger from '../logger';
 import { MempoolBlock, MempoolTransactionExtended, TransactionStripped, MempoolBlockWithTransactions, MempoolBlockDelta, Ancestor, CompactThreadTransaction, EffectiveFeeStats, AuditTransaction } from '../mempool.interfaces';
 import { Common, OnlineFeeStatsCalculator } from './common';
@@ -11,6 +11,7 @@ class MempoolBlocks {
   private mempoolBlockDeltas: MempoolBlockDelta[] = [];
   private txSelectionWorker: Worker | null = null;
   private rustInitialized: boolean = false;
+  private rustGbtGenerator: GbtGenerator = new GbtGenerator();
 
   private nextUid: number = 1;
   private uidMap: Map<number, string> = new Map(); // map short numerical uids to full txids
@@ -342,7 +343,7 @@ class MempoolBlocks {
     // run the block construction algorithm in a separate thread, and wait for a result
     try {
       const { blocks, rates, clusters } = this.convertNapiResultTxids(
-        await napiAddon.make(new Uint8Array(mempoolBuffer)),
+        await this.rustGbtGenerator.make(new Uint8Array(mempoolBuffer)),
       );
       this.rustInitialized = true;
       const processed = this.processBlockTemplates(newMempool, blocks, rates, clusters, saveResults);
@@ -376,7 +377,7 @@ class MempoolBlocks {
     // run the block construction algorithm in a separate thread, and wait for a result
     try {
       const { blocks, rates, clusters } = this.convertNapiResultTxids(
-        await napiAddon.update(
+        await this.rustGbtGenerator.update(
             new Uint8Array(addedBuffer),
             new Uint8Array(removedBuffer),
         ),