On Mon, Nov 30, 2009 at 1:42 PM, David Schmidt <zivildie...@gmail.com> wrote:
> On Mon, Nov 30, 2009 at 5:57 PM, John W. Krahn <jwkr...@shaw.ca> wrote:
>> David Schmidt wrote:
>>> Yes my program has to continue while waiting for the timeout.
>>> You code example doesn't work for me because my program is an entire
>>> Catalyst application which I dont think is a good idea to put into an
>>> eval block.
>>
>> You may not need an eval block:
>>
>> perldoc -f alarm
>> [ SNIP ]
>> If you want to use "alarm" to time out a system call you
>> need to use an "eval"/"die" pair. You can’t rely on the
>> alarm causing the system call to fail with $! set to "EINTR"
>> because Perl sets up signal handlers to restart system calls
>> on some systems. Using "eval"/"die" always works, modulo
>> the caveats given in "Signals" in perlipc.
>>
>>
>> And besides, an eval with a block is compiled at the same time as the rest
>> of your program and doesn't have the run-time overhead of a string eval.
>>
>
> So basically I could create my Signalhandler for the alarm signal, do
> my calculations in the signalhandler and then start another alarm()?
>
> $SIG{ALRM} = {
> # do stuff
> alarm($timeout_2);
> };
> alarm $timeout_1;
>
> And in case this works, is it a good and stable way to solve my problem?
Almost certainly not. *If* it works for you it is relying on some
features specific to your specific operating system and version, and
is not portable, and probably not reliable. Unless have written all
the modules yourself (which is unlikely, as you said this is involves
catalyst), you also don't know everything else that is going on in
your scope. Make sure you read the alarm and perlipc perldocs before
attempting something like this, and pay special attention to both your
OS and Perl version. You *may* not need eval, but it is almost
certainly a good idea. Think of eval {} / if $@ as Perl's approach to
the try/catch idiom of some other languages. You might also want to
take a look at Exception::Base.
We're still not certain what your problem is, though. That makes it
difficult to give you specific advice. The purpose of an alarm or
timeout is normally to interrupt the flow of the program and take some
action when the time is up or if something doesn't happen in the
allotted time.
What you seem to be doing is setting up two independent execution
paths: none of your psuedocode indicates that the alarm breaks into
the main routine or that the execution paths rejoin. If that is really
the case, what you probably really need to do is just spawn a child
process with fork() or IPC::Open3 or similar.
In any case, a real working (or not working as the case may be)
example would go a long way toward helping us help you.
HTH,
-- jay
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