OpenLayers map on homepage may appear blank on new install

[Jeff McKenna]

• initially reported by @tchaddad
• honestly I once saw this happen during the 5.2.0 release candidate process
  • in my case, it only happened on my heavily used machine, with tons of tabs open, in Firefox (that was running a long time, weeks likely, without an update)
    • by "heavily used" I mean I was running the setup.exe installer over and over again into different ports and folders and tabs, and eventually one run caused a blank map in the OpenLayers map on MS4W's homepage (127.0.0.1)
  • clearing the browser cache didn't fix it
  • magically, I closed Firefox (hard restarted it) and I have never seen this issue since

Needs more research (and hopefully steps to replicate here). From quick research I notice other OpenLayers users with somewhat similar reports:

• ​https://github.com/openlayers/openlayers/issues/15839

This will be a tough one. Hmm. Any more findings @tchaddad??

Seems like some sort of memory issue.

Difficult to know yet if a change is needed inside the actual MapServer source code, or to MS4W's embedded OpenLayers code.

[Jeff McKenna]

Oh also, back when it happened, I remember checking and the embedded OpenLayers code wasn't even being called by the browser (and that absolutely confused me).

Eventually I tried a browser restart and have never hit that issue since.

[Jeff McKenna]

and honestly, I can't remember exactly if I needed a browser restart, or hard reboot on that machine, that solved it. In my case it was definitely a memory/CPU issue, on a long running and over-used Firefox instance.

[Jeff McKenna]

related ticket: #543 (upgrade MS4W's embedded ol.js and also make it more lightweight/only include required modules, to hopefully prevent eventual empty map canvas issue)

[TC Haddad]

Agree with your first thought that this could be a resource issue and that smaller OL might help. I went back and double checked, and the server this happened on actually operates on just 4GB RAM, so perhaps under-resourced overall?

[Jeff McKenna]

Hit this again today, after heavy testing in Firefox for the upcoming MS4W 5.2.1 release. Some notes from today's incident:

• this was with a lightweight embedded OpenLayers
• only occurred in Firefox, with template=openlayers calls (CGI GetMap requests are fine, other browsers are fine)
• if I zoomed-in once, map appears
• completely shutdown Firefox, re-opened, and it works fine again on first load

Odd. I wonder if this is related to recent OpenLayers library changes.

Must research more into similar reports filed on the OpenLayers issue tracker (is there a possible workaround?)