From Newsgroup: comp.lang.tcl

Hi,

for starters, sorry - long post - but does the following trigger
anything with someone that suggests what I should be looking for in my
script?

this is running on ubuntu, tcl version 8.6.14.

I have a somewhat complicated script that its scanning lines from my
webserver access logs to find bad actors and block them. The main
process is a long if then else chain of regexp looking for known attack patterns. The script shuts itself down once a day after midnight, and is restarted by a cron job at 12.15am.

Up to a certain point, it would run without this problem, and now it's
coming up at least once a day.

After running for some time it keeps throwing "too many nested
evaluations (infinite loop?)" errors- and the places it throws the error
from changes.

the script is event based. This is open log file proc
proc openAccessLog {} {
log "[now] Opening log file"
set ::accessLog [open "|tail -f -n 30 /var/log/apache2/access.log" r]
fconfigure $::accessLog -blocking 0 -buffering line
fileevent $::accessLog readable [list checkForError $::accessLog]

#initial run after 2 minutes
after 120000 clearExpired
}

it also runs a couple of event procs like this one

proc stopper {} {
set stop_file "/var/tmp/http.stop"
if {[file exists $stop_file]} {
log "[now] closing"
file delete $stop_file
saveSeen
set ::stop "stop"
} else {
#log "." false
}
after 61000 stopper
}

and FYI,

proc now {} {
clock format [clock seconds] -format {%e/%m/%y %T}
}

a recent error is in this proc:

too many nested evaluations (infinite loop?)
while executing
"ParseFormatArgs {*}$args"
(procedure "::tcl::clock::format" line 6)
invoked from within
"clock format [clock seconds] -format {%e/%m/%y %T}"
(procedure "now" line 2)
invoked from within
"now"
(procedure "stopper" line 4)
invoked from within
"stopper"
("after" script)

Also note this script is using ::http::geturl to talk to external APIs, ("https://api.abuseipdb.com/api/v2/check")
and i THINK, this is where the problem starts. From the most recent
crash, the first error was ...

too many nested evaluations (infinite loop?)
while executing
"variable $token"
(procedure "Finish" line 10)
invoked from within
"Finish $token $msg"
(procedure "::http::Connected" line 231)
invoked from within
"::http::Connected $token $proto $phost $srvurl"
(procedure "http::Connect" line 28)
invoked from within
"http::Connect ::http::250 https {} /api/v2/check?ipAddress=172.192.10.125&maxAgeInDays=30"

thanks
Jonathan.
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From Newsgroup: comp.lang.tcl

On 6/21/2025 8:17 PM, Jonathan Kelly wrote:

Hi,

for starters, sorry - long post - but does the following trigger
anything with someone that suggests what I should be looking for in my script?

Hard to say without a more complete code snippet and lots of time. I
suspect your "after" callbacks are interfering with each other, perhaps
over the log file access. You already have two in the sample code, and
there may be more, in ClearExpired, saveSeen, etc. How large does the
log file get?

Also note that the two errors do not seem to be related or due to the
same root cause. The second one with http errors, do you have any
handlers in there if the api is late in responding? You will need to add
code to limit it (like max 5 tries or so) and then just give up on that
call.





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From Newsgroup: comp.lang.tcl

On 23/6/25 03:48, saito wrote:

Hard to say without a more complete code snippet and lots of time. I
suspect your "after" callbacks are interfering with each other, perhaps
over the log file access.  You already have two in the sample code, and there may be more, in ClearExpired, saveSeen, etc. How large does the
log file get?

But isn't the TCL event loop single threaded?
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From Newsgroup: comp.lang.tcl

Jonathan Kelly <jonkelly@fastmail.fm> wrote:

On 23/6/25 03:48, saito wrote:

Hard to say without a more complete code snippet and lots of time.
I suspect your "after" callbacks are interfering with each other,
perhaps over the log file access.  You already have two in the
sample code, and there may be more, in ClearExpired, saveSeen, etc.
How large does the log file get?

But isn't the TCL event loop single threaded?

It is, but you can still get into these situations (usually caused by a
bug).

You mentioned you were also making http calls. Is it possible that
your log entries are arriving faster than the http calls complete (http
is event driven behind the scenes, so calling into http to make a call
will restart the event loop again) causing requests to 'stack up'?


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From Newsgroup: comp.lang.tcl

On 6/22/2025 3:27 PM, Jonathan Kelly wrote:

But isn't the TCL event loop single threaded?

This is a good question. With event driven applications, you usually
don't have a main line of thread that is executing constantly. In that
case, yes, the events may not fire.

However, with such applications, events are fired and processed
repeatedly. So they may indeed interfere with each other.

Here is a nice sample code. See how they intermingle:


proc timer1 {} {puts -nonewline .; after 100 timer1}
proc timer2 {} {puts TIMER....................; after 1000 timer2}

after 1000 timer2; after 100 timer1


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From Newsgroup: comp.lang.tcl

On 6/22/2025 4:10 PM, saito wrote:

proc timer1 {} {puts -nonewline .; after 100 timer1}
proc timer2 {} {puts TIMER....................; after 1000 timer2}

after 1000 timer2; after 100 timer1

Oops, clicked the send button too early. Please change what they print.
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