Chrome DevTools - what does 'Queueing' means in the Timing tab?

Question

In DevTools on the Timing tab you can see the following states:

_

Except 'Queueing' all states are explained in the DevTools documentation. Do you know what browser does in the Queueing phase ? What queue are we talking about ?

Thx

Additionally it seems that Queueing can take place at the beginning of connection setup and also at the beginning of the 'Request/Response' phase ?

Answer 1

From: https://developers.google.com/web/tools/chrome-devtools/network-performance/understanding-resource-timing

Queuing

If a request is queued it indicated that:

• The request was postponed by the rendering engine because it's considered lower priority than critical resources (such as scripts/styles). This often happens with images.
• The request was put on hold to wait for an unavailable TCP socket that's about to free up.
• The request was put on hold because the browser only allows six TCP connections per origin on HTTP 1.
• Time spent making disk cache entries (typically very quick.)

Update from @cyptus comment:

With chrome v76 the network tabs will hide the CORS preflight (OPTIONS) request. The request that triggered this CORS will include the time the (invisible) OPTIONS request took in the queueing timing.

Update from @tamilsweet comment:

To show the CORS preflight follow Chrome not showing OPTIONS requests in Network tab