tendermint/docs/spec/reactors/block_sync/impl.md

## Blockchain Reactor v0 Modules

### Blockchain Reactor

- coordinates the pool for syncing
- coordinates the store for persistence
- coordinates the playing of blocks towards the app using a sm.BlockExecutor
- handles switching between fastsync and consensus
- it is a p2p.BaseReactor
- starts the pool.Start() and its poolRoutine()
- registers all the concrete types and interfaces for serialisation

#### poolRoutine

- listens to these channels:
  - pool requests blocks from a specific peer by posting to requestsCh, block reactor then sends
    a &bcBlockRequestMessage for a specific height
  - pool signals timeout of a specific peer by posting to timeoutsCh
  - switchToConsensusTicker to periodically try and switch to consensus
  - trySyncTicker to periodically check if we have fallen behind and then catch-up sync
    - if there aren't any new blocks available on the pool it skips syncing
- tries to sync the app by taking downloaded blocks from the pool, gives them to the app and stores
  them on disk
- implements Receive which is called by the switch/peer
  - calls AddBlock on the pool when it receives a new block from a peer

### Block Pool

- responsible for downloading blocks from peers
- makeRequestersRoutine()
  - removes timeout peers
  - starts new requesters by calling makeNextRequester()
- requestRoutine():
  - picks a peer and sends the request, then blocks until:
    - pool is stopped by listening to pool.Quit
    - requester is stopped by listening to Quit
    - request is redone
    - we receive a block
      - gotBlockCh is strange


### Go Routines in Blockchain Reactor

![Go Routines Diagram](img/bc-reactor-routines.png)