Low disk space detector (#277)

* - Feature: Disk writes are now blocked early and return an insufficient storage error if free disk space falls below the `--low-diskspace-threshold` value
* Never keep an entry in m_ChunkBlocks that points to a nullptr

1 files changed, 23 insertions, 6 deletions

diff --git a/src/zenstore/include/zenstore/gc.h b/src/zenstore/include/zenstore/gc.h
index e0354b331..fe9857e6a 100644
--- a/src/zenstore/include/zenstore/gc.h
+++ b/src/zenstore/include/zenstore/gc.h
@@ -27,6 +27,7 @@ class HashKeySet;
 class GcManager;
 class CidStore;
 struct IoHash;
+struct DiskSpace;
 
 /** GC clock
  */
@@ -121,6 +122,14 @@ private:
 	GcManager& m_Gc;
 };
 
+/** Interface for querying if we are running low on disk space, used to deny put/writes to disk
+ */
+class DiskWriteBlocker
+{
+public:
+	virtual bool AreDiskWritesAllowed() const = 0;
+};
+
 /** GC orchestrator
  */
 class GcManager
@@ -139,6 +148,9 @@ public:
 
 	GcStorageSize TotalStorageSize() const;
 
+	const DiskWriteBlocker* GetDiskWriteBlocker() { return m_DiskWriteBlocker; }
+	void					SetDiskWriteBlocker(const DiskWriteBlocker* Monitor) { m_DiskWriteBlocker = Monitor; }
+
 #if ZEN_USE_REF_TRACKING
 	void OnNewCidReferences(std::span<IoHash> Hashes);
 	void OnCommittedCidReferences(std::span<IoHash> Hashes);
@@ -151,7 +163,8 @@ private:
 	mutable RwLock				m_Lock;
 	std::vector<GcContributor*> m_GcContribs;
 	std::vector<GcStorage*>		m_GcStorage;
-	CidStore*					m_CidStore = nullptr;
+	CidStore*					m_CidStore		   = nullptr;
+	const DiskWriteBlocker*		m_DiskWriteBlocker = nullptr;
 };
 
 enum class GcSchedulerStatus : uint32_t
@@ -167,10 +180,11 @@ struct GcSchedulerConfig
 	std::chrono::seconds  MonitorInterval{30};
 	std::chrono::seconds  Interval{};
 	std::chrono::seconds  MaxCacheDuration{86400};
-	bool				  CollectSmallObjects = true;
-	bool				  Enabled			  = true;
-	uint64_t			  DiskReserveSize	  = 1ul << 28;
-	uint64_t			  DiskSizeSoftLimit	  = 0;
+	bool				  CollectSmallObjects				= true;
+	bool				  Enabled							= true;
+	uint64_t			  DiskReserveSize					= 1ul << 28;
+	uint64_t			  DiskSizeSoftLimit					= 0;
+	uint64_t			  MinimumFreeDiskSpaceToAllowWrites = 1ul << 28;
 };
 
 class DiskUsageWindow
@@ -196,7 +210,7 @@ public:
 /**
  * GC scheduler
  */
-class GcScheduler
+class GcScheduler : private DiskWriteBlocker
 {
 public:
 	GcScheduler(GcManager& GcManager);
@@ -220,6 +234,8 @@ private:
 	void			   CollectGarbage(const GcClock::TimePoint& ExpireTime, bool Delete, bool CollectSmallObjects);
 	GcClock::TimePoint NextGcTime(GcClock::TimePoint CurrentTime);
 	spdlog::logger&	   Log() { return m_Log; }
+	virtual bool	   AreDiskWritesAllowed() const override { return !m_AreDiskWritesBlocked.load(); }
+	void			   CheckDiskSpace(const DiskSpace& Space);
 
 	spdlog::logger&				 m_Log;
 	GcManager&					 m_GcManager;
@@ -232,6 +248,7 @@ private:
 	std::mutex					 m_GcMutex;
 	std::condition_variable		 m_GcSignal;
 	std::optional<TriggerParams> m_TriggerParams;
+	std::atomic_bool			 m_AreDiskWritesBlocked = false;
 
 	TCasLogFile<DiskUsageWindow::DiskUsageEntry> m_DiskUsageLog;
 	DiskUsageWindow								 m_DiskUsageWindow;