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 mode=map 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?)

[Jeff McKenna]

Hit this again under heavy testing of the upcoming MS4W 5.2.1 release, on a long-running Firefox instance. But this time, after reloading the page, the map appears. Hopefully this will be the case for other MS4W 5.2.1 users, will be watching for reports once 5.2.1 is released.

[Jeff McKenna]

• please test with MS4W 5.2.1-rc1: https://ms4w.com/release/experimental/ms4w_5.2.1_rc1.zip