Scramjet for UNIX: Java acceleration for terminal apps

Main applications

• UNIX command-line tools: Scramjet allows fast UNIX-style command-line tools to be written in Java by avoiding the JVM startup time.
• UNIX terminal applications: Scramjet allows writing efficient ncurses-style fullscreen Unicode ANSI text applications (editors, mail agents, viewers) in Java, with 256-colour support.
• Eclipse hooks: Scramjet allows monolithic Java applications such as Eclipse to be controlled from the UNIX command-line, running commands on demand within the Eclipse JVM, with input/output via the terminal.

Download and License

Hosted on github at http://github.com/uazu/scramjet, and released under the Apache License, Version 2.0

How it works

• On first invocation of Scramjet, a JVM is started for the user and detached.
• Communication with the JVM is via private named pipes (FIFOs) in the ~/.scramjet folder.
• The back-end is pure Java, and the front-end is pure C -- no JNI is used.
• The front-end communicates over the FIFOs to start a given Tool within the JVM and exchanges stdin/stdout/stderr/window-change data over the FIFOs with the Java back end as the tool runs.
• One JVM can serve multiple simultaneous invocations of the same or different tools.
• The background JVM shuts itself down if it has been idle for 15 minutes (configurable).

Advantages of Scramjet

Using Java and Scramjet for writing command-line tools and terminal applications has some advantages and disadvantages compared to starting a JVM each time or writing in C:

• Advantage: The cost of loading and JIT-compiling the classes is paid only once -- after that the tool is 'hot' and starts instantly.
• Advantage: Java and its libraries become convenient for writing small tools, longer than a script but too complex to write quickly in C.
• Advantage: Data may be kept in the JVM and shared between different instances of a tool, e.g. caches, or shared editor buffers.
• Limitation: Java applications use UTF-16 natively rather than UTF-8 or ISO-8859-x, putting them at a disadvantage for bulk text processing compared to C applications written to work with these encodings natively.
• Limitation: Existing Java tools that make use of static variables for per-invocation state may be more difficult to convert to Scramjet. If all else fails, global locks may be a work-around, serialising execution of the tool within the JVM.
• Limitation: Runaway threads in a JVM cannot be killed off. If a Java tool has bugs, the only way to resolve the problem may be to restart the JVM. (You can use the 'sj-threads -l' command to view the live stacktraces of all the running threads.)

Some features:

• Good Unicode handling. Standard input/output/error is converted according to the UNIX locale (e.g. LANG environment variable) as detected by Java on JVM startup.
• For full-screen applications, Unicode output is optimised for UTF-8 and Latin1, otherwise it goes via Java's character encoders. There is no handling of double-width characters yet, and it assumes a 1:1 mapping between Unicode code-points and displayed monospace characters.
• 256-colour output is supported if that is detected from the TERM environment variable and associated terminfo data.
• Raw byte output to standard output/error is possible via direct calls.

Comparison with 'nailgun'

This tool was inspired by nailgun, and has some advantages and disadvantages compared to that tool:

• Advantage: Scramjet is secure because the JVM runs as the user, and all communication passes over local named pipes protected by 0600 permissions.
• Advantage: Scramjet allows curses-style terminal apps to be written because it has a module to pass through window-size information and to enable raw input.
• Advantage: Scramjet has rich convenience classes to make it easy to get started writing various types of apps or tools.
• Same: Scramjet borrows the code from nailgun which diverts System.in/out/err and System.exit(rc) so that they operate as expected within the Tool context.
• Limitation: Scramjet only supports UNIX, because it uses named pipes (FIFOs).
• Limitation: On a multi-user system, each user will have their own Scramjet JVM running. This isn't shared, unlike the JVM in nailgun. In addition, a nailgun server could be run on some other machine on the network, even on another OS.

Using as an Eclipse plugin

Scramjet can be built as an Eclipse plugin. When installed in the Eclipse drop-in folder, Eclipse will load it up and then Eclipse effectively becomes a Scramjet server. Normal Scramjet command-line tools run within the Eclipse JVM, with access to the Eclipse classes. This opens up the possibility of writing command-line tools that query or modify the Eclipse data structures, or that automate Eclipse processes. It is even possible to write a curses-style front end to navigate the Eclipse environment.

Writing full-screen terminal apps

Scramjet provides a curses-like library (although obviously with a Java-oriented API) which supports ANSI terminals such as the Linux console, screen and the various terminals for X, including 256-colour support. The bulk of the code is in Java. The only part in C is the code that sets raw input mode, and that detects the terminal size and catches window-resize signals. The interface can be used directly for simple one-page applications, or via the TiledApp interface for multi-paged tiled applications (like editors).

These pages and files, including applets and artwork, are Copyright (c) 1997-2019 Jim Peters unless otherwise stated. Please contact me if you'd like to use anything not explicitly released, or if you have something interesting to discuss.