Fix new block mempool deletion race condition

backend/src/api/blocks.ts

@@ -529,13 +529,14 @@ class Blocks {
     return await BlocksRepository.$validateChain();
   }
 
-  public async $updateBlocks() {
+  public async $updateBlocks(): Promise<number> {
     // warn if this run stalls the main loop for more than 2 minutes
     const timer = this.startTimer();
 
     diskCache.lock();
 
     let fastForwarded = false;
+    let handledBlocks = 0;
     const blockHeightTip = await bitcoinApi.$getBlockHeightTip();
     this.updateTimerProgress(timer, 'got block height tip');
 
@@ -697,11 +698,15 @@ class Blocks {
       this.updateTimerProgress(timer, `waiting for async callbacks to complete for ${this.currentBlockHeight}`);
       await Promise.all(callbackPromises);
       this.updateTimerProgress(timer, `async callbacks completed for ${this.currentBlockHeight}`);
+
+      handledBlocks++;
     }
 
     diskCache.unlock();
 
     this.clearTimer(timer);
+
+    return handledBlocks;
   }
 
   private startTimer() {

backend/src/api/disk-cache.ts

@@ -52,7 +52,7 @@ class DiskCache {
       const mempool = memPool.getMempool();
       const mempoolArray: TransactionExtended[] = [];
       for (const tx in mempool) {
-        if (mempool[tx] && !mempool[tx].deleteAfter) {
+        if (mempool[tx]) {
           mempoolArray.push(mempool[tx]);
         }
       }

backend/src/api/mempool-blocks.ts

@@ -178,7 +178,7 @@ class MempoolBlocks {
     // prepare a stripped down version of the mempool with only the minimum necessary data
     // to reduce the overhead of passing this data to the worker thread
     const strippedMempool: { [txid: string]: ThreadTransaction } = {};
-    Object.values(newMempool).filter(tx => !tx.deleteAfter).forEach(entry => {
+    Object.values(newMempool).forEach(entry => {
       strippedMempool[entry.txid] = {
         txid: entry.txid,
         fee: entry.fee,

backend/src/api/mempool.ts

@@ -12,7 +12,6 @@ import rbfCache from './rbf-cache';
 
 class Mempool {
   private static WEBSOCKET_REFRESH_RATE_MS = 10000;
-  private static LAZY_DELETE_AFTER_SECONDS = 30;
   private inSync: boolean = false;
   private mempoolCacheDelta: number = -1;
   private mempoolCache: { [txId: string]: TransactionExtended } = {};
@@ -119,7 +118,7 @@ class Mempool {
     return txTimes;
   }
 
-  public async $updateMempool(): Promise<void> {
+  public async $updateMempool(transactions: string[]): Promise<void> {
     logger.debug(`Updating mempool...`);
 
     // warn if this run stalls the main loop for more than 2 minutes
@@ -128,7 +127,6 @@ class Mempool {
     const start = new Date().getTime();
     let hasChange: boolean = false;
     const currentMempoolSize = Object.keys(this.mempoolCache).length;
-    const transactions = await bitcoinApi.$getRawMempool();
     this.updateTimerProgress(timer, 'got raw mempool');
     const diff = transactions.length - currentMempoolSize;
     const newTransactions: TransactionExtended[] = [];
@@ -207,13 +205,15 @@ class Mempool {
       const transactionsObject = {};
       transactions.forEach((txId) => transactionsObject[txId] = true);
 
-      // Flag transactions for lazy deletion
+      // Delete evicted transactions from mempool
       for (const tx in this.mempoolCache) {
-        if (!transactionsObject[tx] && !this.mempoolCache[tx].deleteAfter) {
+        if (!transactionsObject[tx]) {
           deletedTransactions.push(this.mempoolCache[tx]);
-          this.mempoolCache[tx].deleteAfter = new Date().getTime() + Mempool.LAZY_DELETE_AFTER_SECONDS * 1000;
         }
       }
+      for (const tx of deletedTransactions) {
+        delete this.mempoolCache[tx.txid];
+      }
     }
 
     const newTransactionsStripped = newTransactions.map((tx) => Common.stripTransaction(tx));
@@ -270,10 +270,6 @@ class Mempool {
       if (this.mempoolCache[rbfTransaction] && rbfTransactions[rbfTransaction]?.length) {
         // Store replaced transactions
         rbfCache.add(rbfTransactions[rbfTransaction], this.mempoolCache[rbfTransaction]);
-        // Erase the replaced transactions from the local mempool
-        for (const replaced of rbfTransactions[rbfTransaction]) {
-          delete this.mempoolCache[replaced.txid];
-        }
       }
     }
   }
@@ -291,17 +287,6 @@ class Mempool {
     }
   }
 
-  public deleteExpiredTransactions() {
-    const now = new Date().getTime();
-    for (const tx in this.mempoolCache) {
-      const lazyDeleteAt = this.mempoolCache[tx].deleteAfter;
-      if (lazyDeleteAt && lazyDeleteAt < now) {
-        delete this.mempoolCache[tx];
-        rbfCache.evict(tx);
-      }
-    }
-  }
-
   private $getMempoolInfo() {
     if (config.MEMPOOL.USE_SECOND_NODE_FOR_MINFEE) {
       return Promise.all([

backend/src/index.ts

@@ -2,6 +2,7 @@ import express from 'express';
 import { Application, Request, Response, NextFunction } from 'express';
 import * as http from 'http';
 import * as WebSocket from 'ws';
+import bitcoinApi from './api/bitcoin/bitcoin-api-factory';
 import cluster from 'cluster';
 import DB from './database';
 import config from './config';
@@ -179,12 +180,15 @@ class Server {
           logger.debug(msg);
         }
       }
-      await blocks.$updateBlocks();
-      memPool.deleteExpiredTransactions();
-      await memPool.$updateMempool();
+      const newMempool = await bitcoinApi.$getRawMempool();
+      const numHandledBlocks = await blocks.$updateBlocks();
+      if (numHandledBlocks === 0) {
+        await memPool.$updateMempool(newMempool);
+      }
       indexer.$run();
 
-      setTimeout(this.runMainUpdateLoop.bind(this), config.MEMPOOL.POLL_RATE_MS);
+      // rerun immediately if we skipped the mempool update, otherwise wait POLL_RATE_MS
+      setTimeout(this.runMainUpdateLoop.bind(this), numHandledBlocks > 0 ? 1 : config.MEMPOOL.POLL_RATE_MS);
       this.backendRetryCount = 0;
     } catch (e: any) {
       this.backendRetryCount++;

backend/src/mempool.interfaces.ts

@@ -80,7 +80,6 @@ export interface TransactionExtended extends IEsploraApi.Transaction {
   descendants?: Ancestor[];
   bestDescendant?: BestDescendant | null;
   cpfpChecked?: boolean;
-  deleteAfter?: number;
   position?: {
     block: number,
     vsize: number,