Notes: https://pdos.csail.mit.edu/6.824/notes/l-rpc.txt
Video: https://youtu.be/oZR76REwSyA
Prep:
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Golang & it’s RPC package
Why Go?
- support for threads/rpc
- gc
- type safe
Thread Of Execution
Threads from same address space share memory
start (green) thread with go keyword, can exit, stop, resume
Why Threads?
- Express concurrency with threads, IO concurrency
- Multi core parallellism
Challenges
- Race condition
- overcome by avoid sharing
- use locks, race detector from Go (sharing)
- Coordination
- Channels or conditional variables (no sharing)
- Deadlock
Vote
use -race arg with go run to detect race conditions
Crawler
Goals
- IO concurrency
- Fetch url once (no looping)
- Exploit parallellism
RPC
Remotely calling functions(procedures)
f(x, y) function call that happens client side but function is actually implemented at some server f(x, y) {}
https://excalidraw.com/#json=h_2qEFT7-EAPO-r36lXyh,mOxtxUkz5S5Lft2ZvgxG-Q
stubs are automatically generated by compiler
KV Store
rpc.NewServer() to init server
svr.Register()with arg as obj/struct, this will expose public methods of that obj for RPC- public methods starts with uppercase, private’s lowercase
svr.ServeConn(conn)
rpc.Dial() for client init
RPC Semantics Under Failures
- at-least once
- duplicates can occur, exec once or more
- at-most once
- duplicates shouldn’t occur, exec once or don’t (the above KV server)
- exactly once
- very hard, exec exactly once