a2d5758 · distributed-process

251--

252-- Remote endpoints (basically, TCP connections) have the following lifecycle:

253--

254−-- Init ----+---> Invalid

254+-- Init ---+---> Invalid

255-- |

256−-- | /----------------\

256+-- | /--------------\

257−-- | | |

257+-- | | |

258−-- | v |

258+-- | v |

259−-- +---> Valid ----+---> Closing

259+-- +---> Valid ---+---> Closing ---+---> Closed

260−-- | | |

260+-- | | | |

261−-- | | v

261+-- | | | v

262−-- \---------------+---> Closed

262+-- \-------+--------------+------------> Failed

263--

264-- Init: There are two places where we create new remote endpoints: in

265-- requestConnectionTo (in response to an API 'connect' call) and in

266-- handleConnectionRequest (when a remote node tries to connect to us).

267-- 'Init' carries an MVar () 'resolved' which concurrent threads can use to

268−-- wait for the remote endpoint to finish initialization.

268+-- wait for the remote endpoint to finish initialization. We record who

269+-- requested the connection (the local endpoint or the remote endpoint).

269--

270--

270-- Invalid: We put the remote endpoint in invalid state only during

271-- Invalid: We put the remote endpoint in invalid state only during

271-- requestConnectionTo when we fail to connect.

272-- requestConnectionTo when we fail to connect.

281-- the request.

282-- the request.

282--

283--

283-- Closed: The endpoint is put in Closed state after a successful garbage

284-- Closed: The endpoint is put in Closed state after a successful garbage

285+-- collection.

286+--

287+-- Failed: If the connection to the remote endpoint is lost, or the local

284−-- collection, when the endpoint (or the whole transport) is closed manually,

288+-- endpoint (or the whole transport) is closed manually, the remote endpoint is

285−-- or when an IO exception occurs during communication.

289+-- put in Failed state, and we record the reason.

286--

290--

287-- Invariants for dealing with remote endpoints:

291-- Invariants for dealing with remote endpoints:

288--

292--

290-- interleaving bits of payload).

294-- interleaving bits of payload).

291--

295--

292-- INV-CLOSE: Local endpoints should never point to remote endpoint in closed

296-- INV-CLOSE: Local endpoints should never point to remote endpoint in closed

293−-- state. Whenever we put an endpoint in closed state we remove that

297+-- state. Whenever we put an endpoint in Closed state we remove that

294-- endpoint from localConnections first, so that if a concurrent thread reads

298-- endpoint from localConnections first, so that if a concurrent thread reads

295-- the MVar, finds RemoteEndPointClosed, and then looks up the endpoint in

299-- the MVar, finds RemoteEndPointClosed, and then looks up the endpoint in

296-- localConnections it is guaranteed to either find a different remote

300-- localConnections it is guaranteed to either find a different remote