Erlang 及其应用

Erlang及其应用 余锋 2009/03/11 http://blog.yufeng.info

What is Erlang Erlang is a general-purpose programming language and runtime environment. Erlang has built-in support for concurrency, distribution and fault tolerance. Erlang is used in several large telecommunication systems from Ericsson.

What sort of applications is Erlang particularly suitable for Distributed, reliable, soft real concurrent systems. Telecommunication systems, e.g. controlling a switch or converting protocols. Servers for Internet applications, e.g. a mail transfer agent, an IMAP-4 server, an HTTP server or a wap stack Telecommunication applications, e.g. handling mobility in a mobile network or providing unified messaging. Database applications which require soft realtime behaviour. Erlang is good at solving these sorts of problems because this is the problem domain it was originally designed for. Stating the above in terms of features: Erlang provides a simple and powerful model for error containment and fault tolerance (supervised processes).

续上页 Concurrency and message passing are a fundamental to the language. Applications written in Erlang are often composed of hundreds or thousands of lightweight processes. Context switching between Erlang processes is typically one or two orders of magnitude cheaper than switching between threads in a C program. Writing applications which are made of parts which execute on different machines (i.e. distributed applications) is easy. Erlang's distribution mechanisms are transparent: programs need not be aware that they are distributed. The OTP libraries provide support for many common problems in networking and telecommunications systems. The Erlang runtime environment (a virtual machine, much like the Java virtual machine) means that code compiled on one architecture runs anywhere. The runtime system also allows code in a running system to be updated without interrupting the program.

What is OTP? OTP (Open Telecom Platform) is a large collection of libraries for Erlang to do everything from compiling ASN.1 to providing a WWW server. Most projects using "Erlang" are actually using "Erlang/OTP", i.e. the language and the libraries. OTP is also open source.

Erlang的优势 高性能多核心SMP的支持透明分布的支持完善的监控信息商业产品上经过时间的验证成熟轻量进程的支持

为什么其他语言要移植到Erlang虚拟机 语言Reia会成功吗作者看中什么？框架概念成熟度性能模型

Erlang语言特性 简单小巧模式匹配变量单次赋值丰富的库灵活多样的错误处理代码热替换天生的分布式多核支持

Erlang的代码规模 200K行C代码几千行Erlang代码同等的ACE框架代码成熟度尺寸很小适合于嵌入式 1.5M 也适合做桌面程序如p2p

Erlang ERTS是个典型的网络服务器框架 IO处理 kernel poll 如epoll kqueue 定时器处理 timewheel 逻辑处理处理 process coroutine fiber smp

纯消息驱动的系统 多核心处理消息调度器平衡迁移同步和异步无锁编程

多处理器利用技术 线程调度器异步线程 driver发起的线程精巧的锁 process_lock 快速的mutex 进程 PORT 管道通讯

强大的PORT 仿照Unix的哲学: 一切都是文件管道通讯类似CGI 对外世界的重要通道整合其他语言写的模块

与其他系统整合 C节点（EI) Java (jinterface) Cobra TCP/HTTP

RPC 内置的RPC 自动维护节点的up down 知道节点名称就可以通讯轻松分拆服务

热部署功能 不停机维护在线升级系统同时跑新旧代码发现问题在线降级工具化一切自动化

监控功能 OS mon SNMP HTTP

代码安全 代码可远程从网络加载 Diskless 代码可加密强加密防止反编译开源协议

远程维护 强大的内置shell ssh sftp 日志系统

平台移植 Windows （smp支持的不好） *nix 关键语义屏蔽平台变化

和其他网络库的比较 Erlang 相对于 ACE 完整的平台工具开发工具调优工具排错工具跟踪工具

应用障碍 FP语言独特的哲学社区小库偏少

应用案例 Facebook 盛大金山校内很多小startup公司

Q&A 谢谢大家

Erlang 及其应用