Add ChainstateManager::GetMutex(), an alias for ::cs_main

src/validation.h

@@ -868,6 +868,19 @@ class ChainstateManager
     const CChainParams& GetParams() const { return m_chainparams; }
     const Consensus::Params& GetConsensus() const { return m_chainparams.GetConsensus(); }
 
+    /**
+     * Alias for ::cs_main.
+     * Should be used in new code to make it easier to make ::cs_main a member
+     * of this class.
+     * Generally, methods of this class should be annotated to require this
+     * mutex. This will make calling code more verbose, but also help to:
+     * - Clarify that the method will acquire a mutex that heavily affects
+     *   overall performance.
+     * - Force call sites to think how long they need to acquire the mutex to
+     *   get consistent results.
+     */
+    RecursiveMutex& GetMutex() const LOCK_RETURNED(::cs_main) { return ::cs_main; }
+
     std::thread m_load_block;
     //! A single BlockManager instance is shared across each constructed
     //! chainstate to avoid duplicating block metadata.