When does the process done?

I am using browserify and this factor-bundle plugin within gulp. I am outputting the result to writable streams (this is from browserify init):

```
            entries: bundleEntries,
            plugin: [ [ 'factor-bundle', { outputs: bundleOutputs.map(writeScript) } ] ]
```

How can I know when the gulp tasks ends (after all writeScript() calls done)?
