On 11 Jun 2008, at 2:40 pm, j o a r wrote:
On Jun 10, 2008, at 3:17 AM, Graham Cox wrote:
though out of curiosity I wonder if there is a way to do this
"cooperatively" on the main thread without having to break up the
loop doing the actual work. For example, in Carbon one can run the
event loop for a short period or just for one event on each cycle
of the loop - and this code can live in the progress dialog
controller, so it works transparently with respect to the loop that
drives the progress indicator. I'm not sure that approach is
considered "good" in this day and age though I used it a lot on Mac
OS 6/7/8/9. Just wondered if such an approach is feasible in Cocoa.
Yes, you can do that. You would typically use a NSTimer to
repeatedly schedule small pieces of work to be performed on the main
thread. You wouldn't have to use a modal session to do this - It is
certainly not a requirement to lock out the user while processing
data.
Sure, I can easily implement piecemeal work using a timer. That's not
quite the same as I was asking. I was wondering if I could do
something like:
while( notFinished )
{
/* do some work */
letTheEventLoopRunABit();
}
This was a pretty common idiom in the pre-OS X days, though of course
one must bear in mind what the stack looks like when the event loop is
allowed to run. It ain't pretty ;-)
That said - No, it is not considered to be a good approach. It's
almost impossible to implement it in such a way that it doesn't
affect the user experience. It's typically much better, and more
"future safe", to invest your time in a multi-threaded implementation.
Yep, seems to be the way to go. In this case it was an easy change to
allow the work to run on a separate thread. I guess the only thing
that scares me about threads are the sheer number of classes that are
not considered thread-safe, and so calling one accidentally from
another thread.
cheers, Graham
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