Merge pull request #2780 from cuberite/SpawnRace

Fix race condition

src/SpawnPrepare.cpp

@@ -119,7 +119,7 @@ void cSpawnPrepare::PreparedChunkCallback(int a_ChunkX, int a_ChunkZ)
 		float PercentDone = static_cast<float>(m_NumPrepared * 100) / m_MaxIdx;
 		float ChunkSpeed = static_cast<float>((m_NumPrepared - m_LastReportChunkCount) * 1000) / std::chrono::duration_cast<std::chrono::milliseconds>(Now - m_LastReportTime).count();
 		LOG("Preparing spawn (%s): %.02f%% (%d/%d; %.02f chunks / sec)",
-			m_World.GetName().c_str(), PercentDone, m_NumPrepared, m_MaxIdx, ChunkSpeed
+			m_World.GetName().c_str(), PercentDone, m_NumPrepared.load(std::memory_order_seq_cst), m_MaxIdx, ChunkSpeed
 		);
 		m_LastReportTime = Now;
 		m_LastReportChunkCount = m_NumPrepared;

src/SpawnPrepare.h

@@ -1,6 +1,8 @@
 
 #pragma once
 
+#include <atomic>
+
 class cWorld;
 	
 
@@ -25,7 +27,7 @@ protected:
 	int m_MaxIdx;
 
 	/** Total number of chunks already finished preparing. Preparation finishes when this number reaches m_MaxIdx. */
-	int m_NumPrepared;
+	std::atomic<int> m_NumPrepared;
 
 	/** Event used to signal that the preparation is finished. */
 	cEvent m_EvtFinished;