Fixes issues related to parallel updates.

spec/test.cr

@@ -545,6 +545,31 @@ describe "DODB::DataBase" do
 				end
 			end
 		end
+
+		it "does parallel-safe updates" do
+			db = DODB::SpecDataBase.new
+			db_entries_by_name = db.new_index "name", &.name
+
+			# We’ll be storing an integer in the "klass" field, and incrementing
+			# it in forks in a second time.
+			db << Ship.new("test", "0")
+
+			processes = [] of Process
+			fork_count.times do |fork_id|
+				processes << Process.fork do
+					entries_per_fork.times do |entry_id|
+						db_entries_by_name.safe_get "test" do |entry|
+							entry.klass = (entry.klass.to_i + 1).to_s
+
+							db_entries_by_name.update "test", entry
+						end
+					end
+				end
+			end
+			processes.each &.wait
+
+			db_entries_by_name.get("test").klass.should eq((fork_count * entries_per_fork).to_s)
+		end
 	end
 end
 

src/dodb/index.cr

@@ -72,13 +72,16 @@ class DODB::Index(V) < DODB::Indexer(V)
 		nil
 	end
 
+	# FIXME: Unlock on exception.
 	def safe_get(index : String) : Nil
+		@storage.request_lock @name, index
 		internal_key = get_key(index).to_s
 		@storage.request_lock internal_key
 
 		yield get index
 
 		@storage.release_lock internal_key
+		@storage.release_lock @name, index
 	end
 
 	def safe_get?(index : String, &block : Proc(V | Nil, Nil)) : Nil