[FAB-10395] Synchronize access to version cache

This CR makes the access to version cache in couchdb synchronized
as the cache gets loaded during the commit phase but also gets used
during simulation

Change-Id: I1732cf6672fea2ce431b4d6970204f8916ddc527
Signed-off-by: manish <manish.sethi@gmail.com>

Author: manish-sethi

core/ledger/kvledger/txmgmt/statedb/statecouchdb/statecouchdb.go

@@ -74,6 +74,7 @@ type VersionedDB struct {
 	chainName          string                            // The name of the chain/channel.
 	namespaceDBs       map[string]*couchdb.CouchDatabase // One database per deployed chaincode.
 	committedDataCache *versionsCache                    // Used as a local cache during bulk processing of a block.
+	verCacheLock       sync.RWMutex
 	mux                sync.RWMutex
 }
 
@@ -168,6 +169,8 @@ func (vdb *VersionedDB) LoadCommittedVersions(keys []*statedb.CompositeKey) erro
 			}
 		}
 	}
+	vdb.verCacheLock.Lock()
+	defer vdb.verCacheLock.Unlock()
 	vdb.committedDataCache = committedDataCache
 	return nil
 }
@@ -190,6 +193,8 @@ func (vdb *VersionedDB) GetVersion(namespace string, key string) (*version.Heigh
 // GetCachedVersion returns version from cache. `LoadCommittedVersions` function populates the cache
 func (vdb *VersionedDB) GetCachedVersion(namespace string, key string) (*version.Height, bool) {
 	logger.Debugf("Retrieving cached version: %s~%s", key, namespace)
+	vdb.verCacheLock.RLock()
+	defer vdb.verCacheLock.RUnlock()
 	return vdb.committedDataCache.getVersion(namespace, key)
 }
 
@@ -314,6 +319,8 @@ func (vdb *VersionedDB) ApplyUpdates(updates *statedb.UpdateBatch, height *versi
 // ClearCachedVersions clears committedVersions and revisionNumbers
 func (vdb *VersionedDB) ClearCachedVersions() {
 	logger.Debugf("Clear Cache")
+	vdb.verCacheLock.Lock()
+	defer vdb.verCacheLock.Unlock()
 	vdb.committedDataCache = newVersionCache()
 }