Screen cache expiration should consider embedded screens

[slominskir]

If an embedded screen is modified, but the parent screen is not the cache does not clear and the old embedded screen continues to be used. See:

wedm/src/main/java/org/jlab/wedm/business/service/ScreenService.java

Line 44 in acf464a

public HtmlScreen load(String name, List<Macro> macros) throws FileNotFoundException,

[kasemir]

Yes, just noticed that as well.

ScreenService#load does check the modification time of the top level screen.
In many cases the cache thus magically clears.
The web browser might do its own caching, so sometimes need to refresh the web browser a few times, but then the latest version of a display is shown.

.. but the ScreenService doesn't check each embedded display for its modification time.
I'm afraid doing so would be prohibitively slow, especially when displays are fetched via HTTP. The cache offers significant speedup which would be lost by performing an HTTP 'HEAD' check for each embedded screen.

When editing embedded screens, this unfortunately currently requires either a bogus change to the top level screen to force it out of the cache, or a tomcat restart.

A simple 'clear cache' option might be a good middle way. So people working on a screen can access some URL to clear the cache. In the most comfortable version, the https://.../wedm/cache table that shows all files in the cache would have some "Clear" button for each line, plus an overall "Clear All" button.

[slominskir]

Using UNIX touch or on Windows just adding/removing an empty line from parent screen is what I've been doing in development / testing.

In production we happen to have a nightly Tomcat restart CRON job (due to hung PV issue) that also minimizes this issue.

The WEDM app does not set a cache header for text/html so browsers should not be caching screens unless a reverse proxy is setting cache headers.

[kasemir]

We have a few instances of the same smaller screen being embedded in several higher-level screens, but that's actually rare, so it's in fact quite practical to simply touch the higher level screen while editing the embedded one.
So bottom line this is no show stopper.