Alex Tweedly wrote:
When you run this script and you're not connected to the internet here's what happens:
1) If I open the socket with an ip address, e.g. 64.125.128.80, my 5 second timer will fire, and I can close the socket and exit from the routine.
2) If I open the socket with a domain address, e.g. www.webphotospro.com, Mac OS X does a DNS lookup, puts up the rainbow rotating color cursor, and hangs until the DNS lookup fails. On my machine this takes 60 seconds (apparently it's dependent on how many dns servers you have listed).
I'm guessing this is a RunRev bug, but I can't be sure. Basically RunRev hangs for 60 seconds while the DNS lookup takes place during the "open socket" call -- it doesn't send a socket timeout, and it doesn't the "My5SecondTimeout" message either.
Can confirm this?
Yes.
you may have missed the email I sent earlier in this thread, re bug 2117 Engine blocks on DNS query
Take a look at that bug report for more details. You can check for dnsservers - which will prevent the problem occurring in most cases, but there are still some cases where it will fail.
Unfortunately, BZ 2117 is currently being treated as a problem with RevOnline, rather than dealing with the fundamental problem of there being no way to query DNS without the risk of blocking for 40-120 seconds (or longer). Your experiments above prove that it is a fundamental problem, applying even to the "non-blocking" parts of libURL.
Since BZ 2117 has been closed once already as "can't be fixed", you may want to open a Bugzilla report to record the general problem, and simply mention 2117 as a special case of it. Even though it can't be fixed in the normal case (of, e.g., put URL ...) it can easily be provided as a non-blocking function, for use within non-blocking functions such as libURL, or revonline checks.
In the meantime, there is a work-around - but it's pretty ugly .....
1. write a shell script which does a ping to the machine you need to talk to, and saves its results to a log file.
In my case, I created a file called C:\MYPING.BAT which contains
ping www.tweedly.net > c:\ping.txt
(of course, you could create this dynamically, so as to handle any target machine).
2. In your app, "launch" this shell script then start a timer to check for the existence of the log file, and then check the results
local lStart
on mouseUp
delete file "C:/ping.txt"
set hideconsolewindows to true -- Win only
put the seconds into lStart
launch "C:/myping.bat"
send "tryNow" to me in 5 seconds
end mouseUp
on tryNow
local tFile
put "trying" && (the seconds - lStart) & cr after field "lockedField"
if there is a file "C:/ping.txt" then
put URL "file:c:/ping.txt" into tFile
filter tFile with "*Reply*"
if the number of lines in tFile > 0 then
put "success " & word 3 of line 1 of tFile & cr after field "lockedField"
exit "tryNow"
end if
end if
if (the seconds - lStart) > 80 then
put "failure after 80 secs" & cr after field "lockedField"
else
send "tryNow" to me in 5 seconds
end if
end tryNow
3. handle the minor variants needed for each platform ....
(note - tested in my situation where I regularly encounter the problem you described. While I can't think of other circumstances where I would expect this to fail, I haven't done extensive testing of other scenarios).
Or, alternatively, .....
instead of using www.webphotospro.com, use the hard-wired IP address; when that fails, use another hard-wired address to check for the presence of an Internet connection - and only then try again using the hostname (and store the IP address used). This last (blocking) case will only happen when your web site address has changed, and the user has an internet connection, but his DNS servers are either dead or unreachable - which is going to be very rare for any reasonable ISP.
-- Alex.
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