Watchman

2020-04-29
5 min read

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Insert Lead paragraph here.

Alternatives to monitor a folder.

facebook/watchman

A possible alternative to look at [watchman](https://facebook.github.io/watchman). This tool is a native process with Java bindings

Watchman is known to compile and pass its test suite on:

Linux systems with inotify

macOS (uses FSEvents on 10.7+, kqueue(2) on earlier versions)

Windows x64 on Windows 7, Windows Server 2012 R2 and later is currently in beta status.

Their install procedure is currently a bit messy in my opinion, it’s hard to actually find an exact version for linux. You currently have to search through the Github Actions jobs and search for an artifact with a positive size (around 8 MB).

The following artifacts have expired and are no longer able to be downloaded.

watchman does not follow semantic versioning! (Source)

This tool is native however it does have several language bindings, C++ and NodeJS are the one that are documented. However the source code shows additional languages including Java.

Usage of this code is not documented at this time. But by looking at the code, the Java client (and probalby in other languages as well) uses Unix domain socket (named pipe) and Windows Pipes to communicate with the watchman process. Like Docker, with Java Client example there.

Java API usage

// Identifiy the actual socket depending on the platform
WatchmanTransport socket = WatchmanTransportBuilder.discoverTransport(1, SECOND);

WatchmanClient client = new WatchmanClientImpl(WatchmanTransportBuilder.discoverTransport());
client.start();
ListenableFuture<SubscriptionDescriptor> sd = client.subscribe(Paths.get("/etc"), null, new Callback() { (1)
      @Override
      public void call(Map<String, Object> event) {
        // act on event
      }
    });

// unsubscribe
client.unsbscribe(sd.get());

client.close();

1	Use the same semantic as the `subscribe` command internally.

The WatchmanClient exposes almost the same API as the watchman cli tool.

watchexec/watchexec

https://github.com/watchexec/watchexec