Fixed data race in tx mempool

src/block_template.cpp

@@ -322,22 +322,18 @@ void BlockTemplate::update(const MinerData& data, const Mempool& mempool, const
 	}
 
 	// Only choose transactions that were received 5 or more seconds ago, or high fee (>= 0.006 XMR) transactions
-	size_t total_mempool_transactions;
-	{
-		m_mempoolTxs.clear();
-
-		ReadLock mempool_lock(mempool.m_lock);
+	m_mempoolTxs.clear();
 
-		total_mempool_transactions = mempool.m_transactions.size();
+	const uint64_t cur_time = seconds_since_epoch();
+	size_t total_mempool_transactions = 0;
 
-		const uint64_t cur_time = seconds_since_epoch();
+	mempool.iterate([this, cur_time, &total_mempool_transactions](const hash&, const TxMempoolData& tx) {
+		++total_mempool_transactions;
 
-		for (auto& it : mempool.m_transactions) {
-			if ((cur_time > it.second.time_received + 5) || (it.second.fee >= HIGH_FEE_VALUE)) {
-				m_mempoolTxs.emplace_back(it.second);
-			}
+		if ((cur_time > tx.time_received + 5) || (tx.fee >= HIGH_FEE_VALUE)) {
+			m_mempoolTxs.emplace_back(tx);
 		}
-	}
+	});
 
 	// Safeguard for busy mempool moments
 	// If the block template gets too big, nodes won't be able to send and receive it because of p2p packet size limit

src/mempool.h

@@ -34,7 +34,23 @@ class Mempool : public nocopy_nomove
 	void add(const TxMempoolData& tx);
 	void swap(std::vector<TxMempoolData>& transactions);
 
-public:
+	size_t size() const
+	{
+		ReadLock lock(m_lock);
+		return m_transactions.size();
+	}
+
+	template<typename T>
+	void iterate(T&& callback) const
+	{
+		ReadLock lock(m_lock);
+
+		for (const auto& it : m_transactions) {
+			callback(it.first, it.second);
+		}
+	}
+
+private:
 	mutable uv_rwlock_t m_lock;
 	unordered_map<hash, TxMempoolData> m_transactions;
 };

src/p2pool.cpp

@@ -361,7 +361,7 @@ void p2pool::handle_miner_data(MinerData& data)
 		"\ndifficulty              = " << data.difficulty <<
 		"\nmedian_weight           = " << data.median_weight <<
 		"\nalready_generated_coins = " << data.already_generated_coins <<
-		"\ntransactions            = " << m_mempool->m_transactions.size() <<
+		"\ntransactions            = " << m_mempool->size() <<
 		"\n---------------------------------------------------------------------------------------------------------------"
 	);