reduce lock in disklayer (#447)

* Don't block all write access to all buckets when doing GatherReferences/CollectGarbage

2 files changed, 23 insertions, 10 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1badacf21..1ce5c9dc6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,6 +20,7 @@
   - Garbage collect references to currently writing block but keep the block as new data may be added
   - Fix BlockStore::Prune used disk space calculation
   - Don't materialize data in filecas when we just need the size
+  - Don't lock entire disk cache layer when doing GatherReferences/CollectGarbage
 - Improvement: Catch Out Of Memory and Out Of Disk exceptions and report back to requester without reporting an error to Sentry
 - Improvement: If creating bucket fails when storing an item in the structured cache, log a warning and propagate error to requester without reporting an error to Sentry
 - Improvement: Make an explicit flush of the active block written to in blockstore flush
diff --git a/src/zenserver/cache/cachedisklayer.cpp b/src/zenserver/cache/cachedisklayer.cpp
index 7ce713de9..fafc6bbee 100644
--- a/src/zenserver/cache/cachedisklayer.cpp
+++ b/src/zenserver/cache/cachedisklayer.cpp
@@ -1805,12 +1805,18 @@ ZenCacheDiskLayer::CollectGarbage(GcContext& GcCtx)
 {
 	ZEN_TRACE_CPU("Z$::Disk::CollectGarbage");
 
-	RwLock::SharedLockScope _(m_Lock);
-
-	for (auto& Kv : m_Buckets)
+	std::vector<CacheBucket*> Buckets;
+	{
+		RwLock::SharedLockScope _(m_Lock);
+		Buckets.reserve(m_Buckets.size());
+		for (auto& Kv : m_Buckets)
+		{
+			Buckets.push_back(Kv.second.get());
+		}
+	}
+	for (CacheBucket* Bucket : Buckets)
 	{
-		CacheBucket& Bucket = *Kv.second;
-		Bucket.CollectGarbage(GcCtx);
+		Bucket->CollectGarbage(GcCtx);
 	}
 }
 
@@ -2261,12 +2267,18 @@ ZenCacheDiskLayer::GatherReferences(GcContext& GcCtx)
 {
 	ZEN_TRACE_CPU("Z$::Disk::GatherReferences");
 
-	RwLock::SharedLockScope _(m_Lock);
-
-	for (auto& Kv : m_Buckets)
+	std::vector<CacheBucket*> Buckets;
+	{
+		RwLock::SharedLockScope _(m_Lock);
+		Buckets.reserve(m_Buckets.size());
+		for (auto& Kv : m_Buckets)
+		{
+			Buckets.push_back(Kv.second.get());
+		}
+	}
+	for (CacheBucket* Bucket : Buckets)
 	{
-		CacheBucket& Bucket = *Kv.second;
-		Bucket.GatherReferences(GcCtx);
+		Bucket->GatherReferences(GcCtx);
 	}
 }