Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Rich <rich@example.invalid>
Newsgroups: comp.lang.tcl
Subject: Re: Event loop and http::geturl
Date: Tue, 24 Jun 2025 04:21:01 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 38
Message-ID: <103d93c$1q263$1@dont-email.me>
References: <103cf0h$1glgk$1@dont-email.me>
Injection-Date: Tue, 24 Jun 2025 06:21:01 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="49cadd6aad52ccb5031efc129f606c64";
	logging-data="1902787"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1/2C3PNOk19mCtqF+S2m2jC"
User-Agent: tin/2.6.1-20211226 ("Convalmore") (Linux/5.15.139 (x86_64))
Cancel-Lock: sha1:gcTgu5oPN0KQb/xgN70fqfjzyk4=

Jonathan Kelly <jonkelly@fastmail.fm> wrote:
> So, it looks like ::http::geturl is operating asynchronously, despite my 
> program NOT using -command.

It does.  It is documented as such:

man n http:

  Note: The event queue is even used without the -command option.   As a
  side effect, arbitrary commands may be processed while http::geturl is
  running.


The code snippets below are from http-2.9.5.tm which was distributed 
(at least) with 8.6.12:

Buried deep in http::geturl:

        # geturl does EVERYTHING asynchronously, so if the user
        # calls it synchronously, we just do a wait here.
        http::wait $token

And the implementation of http::wait is:

    proc http::wait {token} {
        variable $token
        upvar 0 $token state

        if {![info exists state(status)] || $state(status) eq ""} {
            # We must wait on the original variable name, not the upvar alias
            vwait ${token}(status)
        }

        return [status $token]
    }

And the 'vwait' there reenters the event loop and allows other events 
to be processed.