Introduction

Filewatcher-4D is a proof of concept which demonstrates the interaction of 4D.SystemWorker, the 4D statement CALL WORKER and a platform-native backend (developed with Rust, especially for 4D project structures, safe and highly performant).

Neither 4D plugins nor 4D components need to be used, nor any other runtimes or JIT compilers.

It also demonstrates the possibility to run the above processes completely async, avoiding blocking views and the main loop, but still update relevant objects in your UI (or any other application context) live.

The main use case

for the backend tool was to replace the 4D full text code-search with our own 4D introspection component by introducing a customizable full text search over our 4D code.

Usage

In 4D compiled mode, the app starts immediately with the "Monitor" view. In 4D interpreted mode, you'll have to run the project method launch. The monitoring of a selectable directory can be toggled via the Start/Stop button. The filewatcher settings can only be changed when monitoring is stopped. It can be restarted afterwards.

Some details about design of the 4D app

It should be trivial to extract only the 4D filewatcher backend functionality. The class for the main view controller provides a kind of API for the filewatcher service even without a view. Also, all other classes have been designed in such a way that they can be easily incorporated into existing projects; possibly into 4D components as well.

Also note there is an indicator for cooperative/preemptive mode in the UI. When running compiled, it should switch to preemptive when the watcher is up.

The monitoring on the part of the backend is currently throttled (a.k.a. bounced) to 1 second by the 4D config within the 4D launch project method, because the recorded changes, even with nested directories with ~70.000 files, are so fast that they would be recorded up to 3 times for the same file with different Git events (delete, create, modify) in case you monitor a Git repo. Anyway, this value is configurable.

Some details about the backend

The backend is written in Rust. It is specialized for 4D application structures and performs at C++ speed. Anyway, you may use it for any other needs. To get some infos about this command line app, just run it natively in your terminal and apply argument -h or --help.

We have implemented a cheap async stdin/stdout broker, so it is possible to communicate with the backend over stdin while it is asynchronously streaming file system events to stdout. You may, at any time, pass the following strings, followed by a newline char, to stdin:

version: Writes the SemVer of the backend to stdout
teardown: Initiates a graceful shutdown, which writes some additional feedback to stdout

Excluded files and directories (hard coded defaults)

The following items are invisible for the backend watcher, using glob patterns. See https://en.wikipedia.org/wiki/Glob_(programming) for an explanation what globbing means in the context of OS paths.