Erlang
From AlwaysInnovating
Contents |
Introduction
Erlang is a programming language which has many features more commonly associated with an operating system than with a programming language: concurrent processes, scheduling, memory management, distribution, networking, etc.
Concurrency
- Erlang has extremely lightweight processes whose memory requirements can vary dynamically. Processes have no shared memory and communicate by asynchronous message passing. Erlang supports applications with very large numbers of concurrent processes. No requirements for concurrency are placed on the host operating system.
Distribution
- Erlang is designed to be run in a distributed environment. An Erlang virtual machine is called an Erlang node. A distributed Erlang system is a network of Erlang nodes (typically one per processor). An Erlang node can create parallel processes running on other nodes, which perhaps use other operating systems. Processes residing on different nodes communicate in exactly the same was as processes residing on the same node.
Robustness
- Erlang has various error detection primitives which can be used to structure fault-tolerant systems. For example, processes can monitor the status and activities of other processes, even if these processes are executing on other nodes. Processes in a distributed system can be configured to fail-over to other nodes in case of failures and automatically migrate back to recovered nodes.
Soft real-time
- Erlang supports programming "soft" real-time systems, which require response times in the order of milliseconds. Long garbage collection delays in such systems are unacceptable, so Erlang uses incremental garbage collection techniques.
Hot code loading
- Many systems cannot be stopped for software maintenance. Erlang allows program code to be changed in a running system. Old code can be phased out and replaced by new code. During the transition, both old code and new code can coexist. It is thus possible to install bug fixes and upgrades in a running system without disturbing its operation.
Incremental code loading
- Users can control in detail how code is loaded. In embedded systems, all code is usually loaded at boot time. In development systems, code is loaded when it is needed, even when the system is running. If testing uncovers bugs, only the buggy code need be replaced.
External interfaces
- Erlang processes communicate with the outside world using the same message passing mechanism as used between Erlang processes. This mechanism is used for communication with the host operating system and for interaction with programs written in other languages. If required for reasons of efficiency, a special version of this concept allows e.g. C programs to be directly linked into the Erlang runtime system.
Installation on Touch Book
The minimal erlang system is only 4 MB.
Download cean_installer.bin from CEAN http://cean.process-one.net/downloads/ At the CEAN Downloads page, select "Installer" and "Production" and "Linux ARMEL" and Download.
Before you can install erlang you have to get a copy of the file libsctp.so.1. You can get a compatible .so out of the .deb package from this link [1]. Find the file libsctp.so.1.0.9, and save it to /usr/lib/libsctp.so.1.
Now you are ready to install erlang. Type
chmod 774 cean_installer.bin ./cean_installer.bin
If all goes well you will see the erlang console prompt
Erlang (BEAM) emulator version 5.6.3 [source] [async-threads:0] [kernel-poll:false] Eshell V5.6.3 (abort with ^G) 1>
I use ^G and then "q" to exit the shell. Start it up again with ./cean/start.sh
Install a decent developer editor. SciTE is a nice dev editor and compiles on TB. Download source from [2] and compile:
sudo -s tar -xzvf scite201.tgz cd scintilla/gtk make cd ../.. cd scite/gtk make make install
