Add GC Cancel/Stop (#568)

- GcScheduler will now cancel any running GC when it shuts down.
  - Old GC is rather limited in *when* it reacts to cancel of GC. GCv2 is more responsive.

2 files changed, 16 insertions, 5 deletions

diff --git a/src/zenstore/include/zenstore/blockstore.h b/src/zenstore/include/zenstore/blockstore.h
index 1429a6b02..b748fc8f6 100644
--- a/src/zenstore/include/zenstore/blockstore.h
+++ b/src/zenstore/include/zenstore/blockstore.h
@@ -126,7 +126,7 @@ public:
 	typedef std::vector<size_t>								   ChunkIndexArray;
 
 	typedef std::function<void(const MovedChunksArray& MovedChunks, const ChunkIndexArray& RemovedChunks)> ReclaimCallback;
-	typedef std::function<void(const MovedChunksArray& MovedChunks, uint64_t FreedDiskSpace)>			   CompactCallback;
+	typedef std::function<bool(const MovedChunksArray& MovedChunks, uint64_t FreedDiskSpace)>			   CompactCallback;
 	typedef std::function<uint64_t()>																	   ClaimDiskReserveCallback;
 	typedef std::function<void(size_t ChunkIndex, const void* Data, uint64_t Size)>						   IterateChunksSmallSizeCallback;
 	typedef std::function<void(size_t ChunkIndex, BlockStoreFile& File, uint64_t Offset, uint64_t Size)>   IterateChunksLargeSizeCallback;
@@ -163,7 +163,7 @@ public:
 	void CompactBlocks(
 		const BlockStoreCompactState&	CompactState,
 		uint64_t						PayloadAlignment,
-		const CompactCallback&			ChangeCallback		= [](const MovedChunksArray&, uint64_t) {},
+		const CompactCallback&			ChangeCallback		= [](const MovedChunksArray&, uint64_t) { return true; },
 		const ClaimDiskReserveCallback& DiskReserveCallback = []() { return 0; });
 
 	static const char*			 GetBlockFileExtension();
@@ -230,14 +230,18 @@ public:
 
 	const BlockStoreLocation& GetLocation(size_t Index) const { return m_ChunkLocations[Index]; }
 
-	void IterateBlocks(std::function<void(uint32_t								 BlockIndex,
+	void IterateBlocks(std::function<bool(uint32_t								 BlockIndex,
 										  const std::vector<size_t>&			 KeepChunkIndexes,
 										  const std::vector<BlockStoreLocation>& ChunkLocations)> Callback) const
 	{
 		for (auto It : m_BlockIndexToChunkMapIndex)
 		{
 			size_t ChunkMapIndex = It.second;
-			Callback(It.first, m_KeepChunks[ChunkMapIndex], m_ChunkLocations);
+			bool   Continue		 = Callback(It.first, m_KeepChunks[ChunkMapIndex], m_ChunkLocations);
+			if (!Continue)
+			{
+				break;
+			}
 		}
 	}
 
diff --git a/src/zenstore/include/zenstore/gc.h b/src/zenstore/include/zenstore/gc.h
index f50af8006..486dca3c6 100644
--- a/src/zenstore/include/zenstore/gc.h
+++ b/src/zenstore/include/zenstore/gc.h
@@ -121,6 +121,8 @@ struct GcResult
 	std::chrono::milliseconds WriteBlockMS = {};
 
 	std::chrono::milliseconds ElapsedMS = {};
+
+	bool WasCancelled = false;
 };
 
 class CbObjectWriter;
@@ -129,7 +131,8 @@ void WriteGCResult(CbObjectWriter& Writer, const GcResult& Result, bool HumanRea
 
 struct GcCtx
 {
-	const GcSettings Settings;
+	const GcSettings  Settings;
+	std::atomic_bool& IsCancelledFlag;
 };
 
 typedef tsl::robin_set<IoHash> HashSet;
@@ -341,6 +344,7 @@ public:
 	void RemoveGcReferenceStore(GcReferenceStore& ReferenceStore);
 
 	GcResult CollectGarbage(const GcSettings& Settings);
+	void	 SetCancelGC(bool CancelFlag);
 
 	//////// End GC V2
 
@@ -359,6 +363,7 @@ public:
 	void					SetDiskWriteBlocker(const DiskWriteBlocker* Monitor) { m_DiskWriteBlocker = Monitor; }
 
 private:
+	bool						CheckGCCancel() { return m_CancelGC.load(); }
 	LoggerRef					Log() { return m_Log; }
 	LoggerRef					m_Log;
 	mutable RwLock				m_Lock;
@@ -369,6 +374,8 @@ private:
 
 	std::vector<GcReferencer*>	   m_GcReferencers;
 	std::vector<GcReferenceStore*> m_GcReferenceStores;
+
+	std::atomic_bool m_CancelGC{false};
 };
 
 enum class GcSchedulerStatus : uint32_t