8000 Add comments to aec_block_generator by richcarl · Pull Request #4529 · aeternity/aeternity · GitHub
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Jan 21, 2025
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Add comments to aec_block_generator #4529

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55 changes: 48 additions & 7 deletions apps/aecore/src/aec_block_generator.erl
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Original file line number Diff line number Diff line change
@@ -1,11 +1,27 @@
%%%=============================================================================
%%% @copyright 2018, Aeternity Anstalt
%%% @doc
%%% Module that handle candidate block generation.
%%% Server for collecting transactions into microblocks
%%% @end
%%%=============================================================================
-module(aec_block_generator).

%% The server builds one microbolock at a time, starting with transactions
%% already in the transaction pool. It also subscribes to events about new
%% transactions, adding them to the current microblock as they arrive,
%% avoiding having to query the pool again.
%%
%% When the chain top changes, the current microblock candidate is
%% discarded and a new candidate microblock is started.
%%
%% When a candidate is ready, this fact is published as a `candidate_block`
%% event, and the `get_candidate()` API function can be used to fetch the
%% current candidate (see the `aec_conductor` module). There is however no
%% guarantee that the candidate has not been discarded in the meantime.
%%
%% A single worker process is used for doing the heavy work in the
%% background, for better responsiveness.

%% API
-export([start_link/0, stop/0]).

Expand Down Expand Up @@ -91,13 +107,13 @@ handle_cast(start_generation, State) ->
{noreply, do_start_generation(State)};
handle_cast({worker_done, Pid, {candidate, Candidate, CandidateState}},
State = #state{ worker = {Pid, _} }) ->
%% Only publish non-empty micro-blocks
%% Only publish non-empty microblocks
case aec_blocks:txs(Candidate) of
[] ->
lager:debug("New empty microblock candidate generated, and discarded", []),
lager:debug("Empty microblock candidate prepared", []),
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discarded was the important bit here, I don't like it being removed from the message.

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I was trying to find a wording that made sense. It's not discarded, just not published, and stays in the state ready to be filled when there are incoming tx events. Any better suggestion?

ok;
_ ->
epoch_mining:info("New microblock candidate generated", []),
epoch_mining:info("New microblock candidate ready", []),
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Not an improvement?

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Well, it's getting published as being ready to fetch. Tried to make it contrast with the alternative message above

publish_candidate(Candidate)
end,
State1 = finish_worker(State),
Expand Down Expand Up @@ -149,6 +165,7 @@ code_change(_OldVsn, State, _Extra) ->

%% -- Local functions --------------------------------------------------------

%% When server is told to start generation
do_start_generation(S = #state{ generating = false }) ->
S1 = start_worker(S),
S1#state{ generating = true };
Expand All @@ -158,25 +175,30 @@ do_start_generation(S = #state{ candidate = Candidate }) ->
|| Candidate /= undefined andalso aec_blocks:txs(Candidate) /= [] ],
S.

%% When server is told to stop generation
do_stop_generation(S = #state{ generating = true }) ->
S1 = stop_worker(S),
S1#state{ generating = false };
do_stop_generation(S) ->
S.

%% When a new transaction arrives, either cache it until the current worker
%% has finished, or start a new worker to add it right away.
add_new_tx(S = #state{ worker = Worker }, Tx) ->
case Worker of
undefined -> start_worker_txs(S, [Tx]);
{_WPid, _WRef} -> S#state{ new_txs = [Tx | S#state.new_txs] }
end.

%% Terminate current worker and start a new one
%% (used when the top has changed)
preempt_generation(S, #{ block_hash := NewTop }) ->
S1 = stop_worker(S),
start_worker_block(S1, NewTop).

stop_worker(S = #state{ worker = {WPid, WRef} }) ->
erlang:demonitor(WRef, [flush]),
erlang:exit(WPid, finished),
erlang:exit(WPid, finished), % kill worker process
lager:debug("stopped worker ~p", [WPid]),
S#state{ worker = undefined };
stop_worker(S) ->
Expand All @@ -190,34 +212,50 @@ worker_failed(Reason, S) ->
S1 = finish_worker(S),
start_worker(S1).

%% Update server side bookkeeping when worker is already terminated
finish_worker(S = #state{ worker = {_WPid, WRef} }) ->
erlang:demonitor(WRef, [flush]),
S#state{ worker = undefined }.

%% Creates a fresh microblock candidate on the current top block (used when
%% generation goes from stopped to started)
start_worker(S) ->
case aec_chain:top_block() of
undefined -> S;
Block -> start_worker_block(S, Block)
end.

%% Creates a fresh microblock candidate by querying the transaction pool.
%% Used when the top has changed; there must be no current worker running.
%% Discards and clears the new_tx cache and sets the current candidate to
%% `undefined` so any previously existing candidate can no longer be
%% fetched.
start_worker_block(S = #state{ worker = undefined }, BlockOrBlockHash) ->
{Pid, Ref} = spawn_monitor(fun() -> create_block_candidate(BlockOrBlockHash) end),
lager:debug("Worker ~p created", [Pid]),
S#state{ worker = {Pid, Ref}, new_txs = [], candidate = undefined }.

%% Starts a worker to add transactions from the new_tx cache to the current
%% candidate and clear the new_tx cache. There must be no current worker
%% running. The worker will get the current candidate microblock, returning
%% the updated candidate when done.
start_worker_txs(S = #state{ worker = undefined, candidate = Candidate
, candidate_state = CState }, Txs) ->
, candidate_state = CState }, Txs)
when Candidate =/= undefined ->
{Pid, Ref} = spawn_monitor(fun() -> update_block_candidate(Candidate, CState, Txs) end),
lager:debug("Worker ~p created", [Pid]),
S#state{ worker = {Pid, Ref}, new_txs = [] }.

%% Used when the worker has finished but we may have cached transactions
%% and if so start a new worker to handle them
maybe_start_worker_txs(S) ->
case S#state.new_txs of
[] -> S;
Txs -> start_worker_txs(S, Txs)
end.

%% Generate block candidate
%% Worker: generate a fresh microblock candidate, taking transactions
%% from the transaction pool
create_block_candidate(BlockOrBlockHash) ->
case aec_block_micro_candidate:create(BlockOrBlockHash) of
{ok, NewBlock, NewBlockInfo} ->
Expand All @@ -227,6 +265,7 @@ create_block_candidate(BlockOrBlockHash) ->
end,
ok.

%% Worker: take a microblock candidate and update it, adding transactions
update_block_candidate(Block, BlockInfo, Txs) ->
case aec_block_micro_candidate:update(Block, Txs, BlockInfo) of
{ok, NewBlock, NewBlockInfo} ->
Expand All @@ -235,9 +274,11 @@ update_block_candidate(Block, BlockInfo, Txs) ->
failed_attempt(Reason)
end.

%% Report error and terminate worker
failed_attempt(Reason) ->
gen_server:cast(?MODULE, {worker_done, self(), {failed, Reason}}).

%% Report new candidate microblock and terminate worker
new_candidate(NewBlock, NewBlockInfo) ->
gen_server:cast(?MODULE, {worker_done, self(), {candidate, NewBlock, NewBlockInfo}}).

Expand Down
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