[leo_storage] replicator/5 can receive messages generated by gen_server:call/cast

[mocchira]

Background

• We call erlang:receive at https://github.com/leo-project/leofs/blob/1.3.3-rc3/apps/leo_storage/src/leo_storage_replicator.erl#L106-L125 when leo_storage_replicator:replicate/5 called.
• There are two kind of caller processes
  • process spawned by rex when handling a request from leo_gateway (online task)
  • process spawned as a gen_server (leo_mq_consumer) when consuming an item stored in leo_mq (offline task)

Problem

No problem when handling online tasks.
The problem can happen when handling offline tasks because a caller process is a gen_server so calling erlang:receive can receive messages unintentionally generated by gen_server:call/cast.

Solution

We are going to add a tag (in order to receive messages ONLY we are using in leo_storage_replicator) into all messages.

Reference

How the gen_server manages send/receive messages.

• https://github.com/erlang/otp/blob/OTP-19.3.1/lib/stdlib/src/gen_server.erl