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def handle_call({:fetch_block, block_number}, state) do # Fetch block data from third-party API block_data = fetch_block(block_number) {:reply, block_data, state} end 13

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task = Task.async(fn -> fetch_block(1_000_000) end) Task.await(task) # {:ok, %Block{number: 1_000_000, ...}} 16

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Task.async_stream Task.yield_many 17

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block_range_batches |> Task.async_stream(&fetch_blocks(&1)) |> Task.yield_many() 18

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block_range_batches |> Task.async_stream( &fetch_blocks(&1), max_concurrency: 4 ) |> Task.yield_many() 21

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def init(_) do state = build_state() send(self(), :start_task) {:ok, state} end def handle_info(:start_task, state) %Task{ref: ref} = task = Task.async(fn -> do_expensive_work(state) end) Task.run(task) {:noreply, Map.put(state, :task_ref, ref)} end 36

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def handle_info({ref, expensive_work_result}, %{task_ref: ref} = state) # Flush messages related to the monitor Process.demonitor(ref, [:flush]) # Do something with the result process_result(expensive_work_result) send(self(), :start_task) {:noreply, %{state | task_ref: nil}} end 38

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children = [ {Task.Supervisor, name: BlockScout.TaskSupervisor} ] Supervisor.start_link(children, strategy: :one_for_one) 42

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def handle_info(:start_task, state) do %Task{ref: ref} = Task.Supervisor.async_nolink( BlockScout.TaskSupervisor, fn -> do_expensive_work(state) end ) {:noreply, Map.put(state, :task_ref, ref)} end 43

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def handle_info({ref, expensive_work_result}, %{task_ref: ref} = state) # Flush messages related to the monitor Process.demonitor(ref, [:flush]) # Do something with the result process_result(expensive_work_result) send(self(), :start_task) {:noreply, %{state | task_ref: nil}} end 45

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def handle_info({:DOWN, ref, :process, pid, reason}, %{task_ref: ref} = state) do # Decide how to respond to a failure handle_process_failure() {:noreply, %{state | task_ref: nil} end 47

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Repo.insert 51

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Ecto.Repo.insert_all/3 52

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blocks = [%{...}, %{...}, ...] Repo.insert_all(Block, blocks, []) 53

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blocks = [%{...}, %{...}, ...] Repo.insert_all( Block, blocks on_conflict: :replace_all, conflict_target: :number ) 55

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Ecto.Repo.stream/2 58

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query = unfetched_address_balances_query() reducer = fn (item, list) -> [item | list] end initial = [] Repo.transaction( fn -> query |> Repo.stream() |> Enum.reduce([], reducer) end ) 59

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query = unfetched_address_balances_query() reducer = fn (item, list) -> [item | list] end initial = [] Repo.transaction( fn -> query |> Repo.stream(timeout: :infinity) |> Enum.reduce([], reducer) end, timeout: :infinity ) 60

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defmodule BlockScout.MarketRates.Cache do use GenServer # ... def handle_info(:refresh_rates, _state) do rates = fetch_rates() {:noreply, rates} end def handle_call({:fetch_ticker, ticker}, state) do {:reply, Map.get(state, :ticker), state} end end 62

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def init(_) do :ets.new( :market_rates_cache, [:set, :named_table, :public, read_concurrency: true, write_concurrency: true] ) send(self(), :refresh_rates) {:ok, %{}} end 65

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def handle_info(:refresh_rates, state) do rates = fetch_rates() insert_into_ets(data) {:noreply, state} end def all_tickers do :ets.tab2list(:my_app_cache) end def fetch_ticker(ricker) do case :ets.lookup(:market_rates_cache, ticker) do [item] -> {:ok, item} _ -> {:error, :not_found} end end 66

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Phoenix.PubSub 69

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children = [ # ... {Registry, keys: :duplicate, name: Blockchain.Events} ] 70

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Registry.register(Blockchain.Events, :new_block, []) 71

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Registry.dispatch(Blockchain.Events, :new_block, fn entries -> for {subscriber_pid, _registered_val} <- entries do send(subscriber_pid, {:new_block, block}) end end) 72

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