Russ Cox's lecture on Go

Why Go?

• an answer to the problems of scalability at Google
  • 10^6+ machines design point
  • it's routine to be running on 1000 machines
  • constantly writing programs that coordinate with each other
    • sometimes MapReduce works, other times it doesn't

Who uses Go at Google

• SPDY proxy for Chrome on mobile devices uses a Go-written Data Compression Proxy
• dl.google.com
• YouTube MySQL balancer
• the target is network servers, but it's a great gen. purp. language
• Bitbucket, bitly, GitHub, Dropbox, MongoDB, Mozilla services, NY Times, etc.

Concurrency

• "Communicating Sequential Processes", by Hoare, 1978
  • strongly encouraged to read
  • in some sense, a generalization of UNIX pipelines
• Bell Labs had some languages developed for concurrency in 80's, 90's:
  • Pan, Promela, Newsqueak, Alef, Limbo, Libthread, Concurrent ML
• Google developed Go in the 2000s

There's no goroutine IDs

• "There's no goroutine IDs, so I can't kill my threads"
  • This is what channels are for: just tell your thread via a channel to shut itself off
  • Also, it's kind of "antisocial" to kill them.
    • What we mean is that your program is prolly not gonna work very well if you keep killing your threads like that

Channels vs. Mutexes

• if you need a mutex, use a mutex
• if you need condition variable, think about using a channel instead
• don't communicate by sharing memory, you share memory by communicating

Network channels

• it'd be great to have the equivalent for a network channel
• if you take local abstractions (like channels) and use them in a new context like a network, ignoring failure modes (etc), then you're gonna run into trouble

Scale of engineering efforts

In 2011, Google had:

• 5000+ developers
• 20+ changes per minute
• 50% code base changes every month (files? not lines probably)
• 50 million test cases executed per day
• single code tree projects

A new language was needed to fix the problems that other languages had with software engineering at this scale

The scale of compilation matters.

• When you compile a package A that depends on B, most (all?) languages need to compile B first
• Go doesn't.
• Dependencies like these at the scale of Google projects slow down compilation if you use a traditional language
  • gets worse with "deeper" dependencies A->B->C->D->...
• Example: at some point they found a postscript interpreter compiled in a server binary for no reason due to weird deps

Interfaces vs. inheritance

• inhertance hierarchies are hard to get right and if you don't they are hard to change later
• interfaces are much more informal and clearer about who owns and supplies what parts of the program

Readability and simplicity

• Dick Gabriel quote:

  "I'm always delighted by the light touch and stillness of early programming languages. Not much text; a lot gets done. Old programs read like quiet conversations between a well-spoken research worker and a well-studied mechanical colleague, not as a debate with a compiler. Who'd have guessed sophistication bought such noise?"

• Simplify syntax
• Avoid cleverness: ternary operators, macros
• Don't let code writing be like "arguing with your compiler"
• Don't want to puzzle through code 6 months later

Design criteria

• started by Rob Pike, Robert Griesemer and Ken Thompson in late 2007
• Russ Cox, Ian Lance Taylor joined in mid-2008
• design by consensus (everyone could veto a feature, if they didn't want it)

Generics

• Russ: "Don't use *list.List, you almost never need them. Use slices."
  • Generics are not bad, just hard to do right.
    • Early designers for Java generics also agreed and warned Go designers to be careful
      • Seems like they regretted getting into that business

Enginering tools

• when you have millions of lines of code, you need mechanical help
  • like changing an API
• Go designed to be easy to parse (not like C++)
• standard formatter
• Means you can't tell a mechanical change from a manual change
  • enables automated rewrites of code

More automation

• fix code for API updates
  • early Go versions API changed a lot
  • Google had a rewriter that would fix your code which used the changed APIs
• renaming struct fields, variables w/ conflict resolution
• moving packages
• splitting of packages
• code cleanup
• change C code to Go
• global analysis that figure out what are all the implementors of an interface for instance

State of Go

• Go 1.4 released in Decembeer 2014
• Go 1.5 has toolchain implemented in Go, not in C
  • concurrent GC
  • Go for mobile devices
  • Go on PowerPC, ARM64
• Lots of people use it
• Go conferences outside of Google/Go

Q&A

• Go vs C/C++
  • Go is garbage collected, biggest difference, so slower
  • Go can be faster than Java sometimes
  • once you're aware of that, you can write code that runs faster than C/C++ code
  • no reason that code that doesn't allocate memory shouldn't run as fast as C/C++
• Goal to use Go outside Google?
  • Yes! Otherwise the language would die?
  • You get a breadth of experts that give you advice and write tools, etc.
    • C++ memory model guy gave feedback on Go memory model
      • Very usefl
  • Not trying to replace anything like language X
    • but they were using C/C++ and didn't want to anymore
    • however Python and Ruby users are switching to Go more
      • Go feels just as light but statically type checked
• Studies about benefits of Go?
  • not a lot of data collected