What does “Lock” mean in the Firebug Net panel?

Question

I use Firebug 1.5.2, and when testing a site before releasing products, I see a huge amount of time spent on parts of the "Block" requests.

What does blocking mean?

Answer 1

The “lock” previously (earlier versions of FireBug) was called “Queuing”. In fact, this means that the request is in the queue, waiting for an available connection. As far as I know, the number of permanent connections by default is limited in recent versions of Firefox to 6, IE8 is also 6. Previously, it was only 2. It can be changed by the user in the browser settings.
Also, as I know, when loading a javascript file, all other resources (css, images) are blocked

Answer 2

Blocking is a term used to describe an event that stops other events or code from being processed (within the same thread).

For example, if you use “blocking” sockets, then the code after the socket request will not be processed until the request is complete (within the same thread).

Asynchronous actions (without blocking) would simply execute the request and let another code run while the request was running in the background.

In your situation, this basically means that certain parts of the firebug / browser cannot be activated until the other parts are completed. That is, it waits for the image to load before uploading.

Answer 3

As far as I know, two reasons make components block other users from loading.

• The browser forces (but usually customizable) the limit on how many concurrent resources can be downloaded from a specific host at a time.
• Built-in javascript that can make the browser wait and see if you need to continue loading the rest of the components (just in case javascript redirects or replaces the contents of the page)

Answer 4

This means waiting for a connection. As explained by the official Mozilla documentation , “Lock” is “Time spent in queue waiting to connect to the network.” This may be due to Firefox putting its internal limit on parallel connections, as explained here and in the answers here.

It can also mean "wait because the server is busy." One of the possible reasons for "blocking" the time is missing in the official documentation given above: this can happen when the server cannot provide the connection on time, because it is overloaded. In this case, the connection request is queued on the server until it is processed after the workflow becomes free [ source ].

In a technical sense, such a connection has not yet been established, because the request is waiting for accept() from the server [ source ]. And perhaps that is why it is included in the "Blocking" of Firefox, since it can also be considered "Time spent in the queue waiting for a network connection."

(This behavior is not compatible with Firefox 51, though: for the first URL that is called on a new tab, the time before the server accepts the connection request does not count at all in the Timing tab - only for subsequent URLs. Any of both behaviors can be a mistake, I don’t know which one.)