Handle Already Dropped Caller

[samharnack]

I periodically get a match error when a caller is dropped that doesn't exist in Terminator.calls. I'm not sure how to test for this or even how it gets in this state in the first place. Does anyone have any insight into this?

[chrismccord]

Can you share a specific match error, or the line that fails? We are matching on state.calls in a couple places, so I just want to be sure before I review. Thanks!

[samharnack]

It was matching against an empty map %{}.

I don't have the exact error anymore; I'll see if I can get it to happen again and provide the stack trace.

This could also be added as another case here: https://github.com/phoenixframework/flame/blob/main/lib/flame/terminator.ex#L202

I don't know if its related, but I'm also seeing this error occasionally:

** (ErlangError) Erlang error: :timeout

lib/flame/runner.ex:143 FLAME.Runner.call/4
lib/flame/pool.ex:250 anonymous fn/6 in FLAME.Pool.do_call/4
lib/flame/pool.ex:326 FLAME.Pool.caller_checkout!/5
lib/task/supervised.ex:101 Task.Supervised.invoke_mfa/2
lib/task/supervised.ex:36 Task.Supervised.reply/4

[samharnack]

Finally got the exception 🎉

** (MatchError) no match of right hand side value: %{
#Reference<70218.4250035323.1243086849.196657> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4631.0>, timer: #Reference<70218.4250035323.1243086849.196658>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196670> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4632.0>, timer: #Reference<70218.4250035323.1243086849.196671>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196712> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4636.0>, timer: #Reference<70218.4250035323.1243086849.196713>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196880> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4646.0>, timer: #Reference<70218.4250035323.1243086849.196881>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196901> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4650.0>, timer: #Reference<70218.4250035323.1243086849.196902>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196908> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4651.0>, timer: #Reference<70218.4250035323.1243086849.196909>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196919> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4652.0>, timer: #Reference<70218.4250035323.1243086849.196920>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086849.196941> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4661.0>, timer: #Reference<70218.4250035323.1243086849.196942>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086853.194886> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4656.0>, timer: #Reference<70218.4250035323.1243086853.194887>, placed_child_ref: nil, placed_caller_ref: nil, link?: false},
#Reference<70218.4250035323.1243086853.194899> => %FLAME.Terminator.Caller{from_pid: #PID<70218.4657.0>, timer: #Reference<70218.4250035323.1243086853.194900>, placed_child_ref: nil, placed_caller_ref: nil, link?: false}
}


lib/flame/terminator.ex:333 FLAME.Terminator.drop_caller/2
lib/flame/terminator.ex:203 FLAME.Terminator.handle_info/2
gen_server.erl:2173 :gen_server.try_handle_info/3
gen_server.erl:2261 :gen_server.handle_msg/6
proc_lib.erl:329 :proc_lib.init_p_do_apply/3

[josevalim]

It may be better to make sure we don't call drop_caller if it has been dropped already, rather than making every call now potentially "soft"?