From b335dd7cccd20a539e165145e7e89b2b2e185ab4 Mon Sep 17 00:00:00 2001
From: Stefan Boberg <stefan@boberg.org>
Date: Thu, 27 May 2021 18:14:44 +0200
Subject: Added locks to protect against races in parallel oplog updates

---
 zenserver/projectstore.cpp | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

(limited to 'zenserver/projectstore.cpp')

diff --git a/zenserver/projectstore.cpp b/zenserver/projectstore.cpp
index c94a8fe35..6cf5dc161 100644
--- a/zenserver/projectstore.cpp
+++ b/zenserver/projectstore.cpp
@@ -269,13 +269,19 @@ ProjectStore::Oplog::ReplayLog()
 IoBuffer
 ProjectStore::Oplog::FindChunk(Oid ChunkId)
 {
+	RwLock::SharedLockScope _(m_OplogLock);
+
 	if (auto ChunkIt = m_ChunkMap.find(ChunkId); ChunkIt != m_ChunkMap.end())
 	{
+		_.ReleaseNow();
+
 		return m_CasStore.FindChunk(ChunkIt->second);
 	}
 
 	if (auto FileIt = m_FileMap.find(ChunkId); FileIt != m_FileMap.end())
 	{
+		_.ReleaseNow();
+
 		std::filesystem::path FilePath = m_OuterProject->RootDir / FileIt->second.ServerPath;
 
 		return IoBufferBuilder::MakeFromFile(FilePath.native().c_str());
@@ -283,6 +289,8 @@ ProjectStore::Oplog::FindChunk(Oid ChunkId)
 
 	if (auto MetaIt = m_MetaMap.find(ChunkId); MetaIt != m_MetaMap.end())
 	{
+		_.ReleaseNow();
+
 		return m_CasStore.FindChunk(MetaIt->second);
 	}
 
@@ -292,6 +300,8 @@ ProjectStore::Oplog::FindChunk(Oid ChunkId)
 void
 ProjectStore::Oplog::IterateFileMap(std::function<void(const Oid&, const std::string_view&)>&& Fn)
 {
+	RwLock::SharedLockScope _(m_OplogLock);
+
 	for (const auto& Kv : m_FileMap)
 	{
 		Fn(Kv.first, Kv.second.ClientPath);
@@ -301,6 +311,8 @@ ProjectStore::Oplog::IterateFileMap(std::function<void(const Oid&, const std::st
 bool
 ProjectStore::Oplog::AddFileMapping(Oid FileId, IoHash Hash, std::string_view ServerPath, std::string_view ClientPath)
 {
+	// NOTE: Caller must hold an exclusive lock on m_OplogLock
+
 	if (ServerPath.empty() || ClientPath.empty())
 	{
 		return false;
@@ -328,12 +340,16 @@ ProjectStore::Oplog::AddFileMapping(Oid FileId, IoHash Hash, std::string_view Se
 void
 ProjectStore::Oplog::AddChunkMapping(Oid ChunkId, IoHash Hash)
 {
+	// NOTE: Caller must hold an exclusive lock on m_OplogLock
+
 	m_ChunkMap.emplace(ChunkId, Hash);
 }
 
 void
 ProjectStore::Oplog::AddMetaMapping(Oid ChunkId, IoHash Hash)
 {
+	// NOTE: Caller must hold an exclusive lock on m_OplogLock
+
 	m_MetaMap.emplace(ChunkId, Hash);
 }
 
@@ -342,6 +358,11 @@ ProjectStore::Oplog::RegisterOplogEntry(CbObject Core, const OplogEntry& OpEntry
 {
 	ZEN_UNUSED(TypeOfUpdate);
 
+	// For now we're assuming the update is all in-memory so we can hold an exclusive lock without causing
+	// too many problems. Longer term we'll probably want to ensure we can do concurrent updates however
+
+	RwLock::ExclusiveLockScope _(m_OplogLock);
+
 	using namespace std::literals;
 
 	// Update chunk id maps
-- 
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