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Learn channel-from-from-golang-source-code

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Genchi Lu

This document summarizes a Pull Request (PR) that improves the performance of receiving from an empty closed channel in Go. It begins by describing the PR title and motivation to speed up non-blocking receives on closed channels. It then provides background on how channels work in Go, explaining their circular queue mechanism and how goroutines can block on channel operations. The document details how the PR implementation checks if the channel is empty and closed before locking, avoiding the overhead of locking in this common case. It concludes with a demo of the performance improvement using benchmarks and profiling tools.

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source code W golang channel G7
Agenda A PR title : runtime: speed up receive on empty closed channel How channel work How the PR do to improve performance Analysis
A PR title : runtime: speed up receive on empty closed channel
runtime: speed up receive on empty closed channel Currently, nonblocking receive on an open channel is about 700 times faster than nonblocking receive on a closed channel. This change makes closed channels equally fast.
How channel work
channel mechanism: circular queue
channel mechanism: block goroutine would be blocked if executing channel operations. v <- chan chan <- v
channel mechanism: non-block select { case msg := <-chan fmt.Println(Receive msg from channel) default: fmt.Println(No message received) }
channel mechanism: send to full channel Keep data in goroutine Add goroutine to sendq
channel mechanism: send to full channel Add goroutine to recvq
source code: chan <- val close block full empty recvq return false false true true false true - - - panic false - - false true false - false true true false true true true (block until complete) true
source code: val <- chan close block empty empty sendq return (select, received) false false true true (false, false) true - - true (true, false) false - - false (true, true) - - false true (true, true) false true true true (block until complete) (true !close)
How the PR do to improve performance
partial pseudo code in receive: go1.14 if !block && empty && !close return lock() if close && empty unlock return true, false
partial pseudo code in receive: cb14bd8 if !block && empty if !close return else return true, false lock()
Analysis
Life demo demo: run benchmark & pporf
QA

More Related Content

Learn channel-from-from-golang-source-code

  • 1. source code W golang channel G7
  • 2. Agenda A PR title : runtime: speed up receive on empty closed channel How channel work How the PR do to improve performance Analysis
  • 3. A PR title : runtime: speed up receive on empty closed channel
  • 4. runtime: speed up receive on empty closed channel Currently, nonblocking receive on an open channel is about 700 times faster than nonblocking receive on a closed channel. This change makes closed channels equally fast.
  • 7. channel mechanism: block goroutine would be blocked if executing channel operations. v <- chan chan <- v
  • 8. channel mechanism: non-block select { case msg := <-chan fmt.Println(Receive msg from channel) default: fmt.Println(No message received) }
  • 9. channel mechanism: send to full channel Keep data in goroutine Add goroutine to sendq
  • 10. channel mechanism: send to full channel Add goroutine to recvq
  • 11. source code: chan <- val close block full empty recvq return false false true true false true - - - panic false - - false true false - false true true false true true true (block until complete) true
  • 12. source code: val <- chan close block empty empty sendq return (select, received) false false true true (false, false) true - - true (true, false) false - - false (true, true) - - false true (true, true) false true true true (block until complete) (true !close)
  • 13. How the PR do to improve performance
  • 14. partial pseudo code in receive: go1.14 if !block && empty && !close return lock() if close && empty unlock return true, false
  • 15. partial pseudo code in receive: cb14bd8 if !block && empty if !close return else return true, false lock()
  • 17. Life demo demo: run benchmark & pporf
  • 18. QA