Re: NSTask interactive question
Re: NSTask interactive question
- Subject: Re: NSTask interactive question
- From: Chris Suter <email@hidden>
- Date: Thu, 30 Nov 2006 09:39:06 +1100
One thing to be wary of (although it might not occur in your case),
is that both writeData and availableData can block if there isn't
sufficient buffer space. I'm guessing that Ruby's gets, puts and
$stdout.flush might also block. So, in certain circumstances, you
could get a deadlock.
You could demonstrate the deadlock by making s have more than one
suitably large lines. Of course this may not be possible in your case
but I think there would still be other circumstances where you'd get
a deadlock (they're slightly more difficult to demonstrate).
- Chris
On 30/11/2006, at 7:17 AM, Shawn Erickson wrote:
On 11/29/06, Matt Neuburg <email@hidden> wrote:
I have an NSTask which is a Ruby interactive script. The Ruby
script just
loops on standard input, like this:
while (s = gets)
puts gk.crunch(s) # never mind what that does
$stdout.flush
end
I'm launching this NSTask and then I'm repeatedly sending input at
it and
retrieving the output, all in a single routine, without using
notifications,
like this:
NSString* input = [NSString stringWithFormat: @"%@\n", s];
NSFileHandle* fh = [[task standardInput] fileHandleForWriting];
[fh writeData:[input dataUsingEncoding: NSMacOSRomanStringEncoding]];
NSFileHandle* fh2 = [[task standardOutput] fileHandleForReading];
NSString* output = [[[NSString alloc] initWithData: [fh2
availableData]
encoding: NSUTF8StringEncoding] autorelease];
I'm just doing that over and over again, supplying input and
retrieving
output in a single step. It's working fine. My question is: even
though it's
working, am I in fact cruising for a bruising? Must I instead use
the more
complicated readInBackgroundAndNotify architecture? m.
Nothing in the above is ensuring that you get a complete response from
the task since availableData may be a subset of what the task has so
far been able to generate after you send out the input. Also nothing
ensures that you might not flood the task with input so that the
output you read is unrelated to what you just sent down.
You don't need to use read in background but you do need to ensure you
are in sync with your task in some fashion (note read in background
wouldn't solve this issue for you either).
-Shawn
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