Concurrency and Message Passing in Newsqueak

前言

参见链接： Concurrency and Message Passing in Newsqueak

Rob Pike 介绍自己在 Plan 9 发明的 Newsqueak 语言的演讲。对于Golang 或者Erlang的理解很有帮助。

讲义

Concurrency

The world is concurrent, but computers are not.

This is a profound(深远的) mismatch

Two approches:

1. Make(interface to) the world sequential
2. Make software concurrent

This talk is about approach 2.

NOT

A common approach to concurrency is to consider it a necessary evil.

The world is concurrent, computers are becoming multicore,
it's all ugly, yuck, better learn it.

NO!

This talk is about how concurrent software makes programmers - not machines - more effcient.

Concurrency Programming provides a model for interface and design the simplifies even nonparallel software.

But still, when it’s parallel you want…

State

an executing process has:

* program counter(PC)
* stack

Write this as (PC, stack). This is a powerful way to represent state. (Consider stack traceback.)

A concurrent program is (PC, stack)+.

Exponentially more powerful, yet conceptually just as easy to understand - and only linearly harder to debug.

What do we need to do?

The Model

Think about software as

* interacting
* independently executing
* processes

In Hoare’s original formulation,

Communicating Sequential Processes

Deliberately(故意的) missing terminology(专有名词):

* threads, share memory, locks, semaphores, ...

This is not Andrew Birrell’s model, which is too low-level for easy programming.

Selected History

Hoare, 1978:CSP

- processes and communication

Cardelli & Pike, 1985:Squeak

- CSP with channels(but really just a toy)
- for interactive programs

Pike, 1988:Newsqueak

- a full, interpreted, experimental language

Winterbottom, 1995:Alef

- a full, compiled, systems language

Dorward, Pike, Winterbottom, 1996:Limbo

- approximately JIT-ed Newsqueak

Overview

* An overview of Newsqueak
* Processes
* Channels
* Programs
* Interface design
* System software

An overview of Newsqueak

* Looks a lot like Sawzall(but recher)
* Pascal-like type declarations
* C-like control structures
* Functions are just variables(lambdas, prog)
* Process controls(begin, become)
* Channels are first-class citizens
* Memory: value semantics(警戒)(no sharing)