Re: Semaphores or not?
Deniz Dogan wrote:
....
Is it better to create two threads which read information from each file
and use Semaphore based barrier synchronization to change values of a
row of the table only once (with both the information from original.txt
and translation.txt at once) ...OR... is it better to first sequentially
read original.txt and then use table.setValueAt(Object, int, int) to set
the correct values from translated.txt?
Phew, I hope you understand what I'm trying to say.
I'm assuming the processing is reasonably simple.
If the files are not cached in memory at the time the job runs, it
should run at disk read speed. If both files are on the same disk,
reading one file at a time will tend to be faster because it reduces
disk head movement. If they are on different disks reading them in
parallel may be faster than one at a time, because you get to make
effective use of both disk heads.
If the files are cached in memory, the job's CPU time becomes the
critical factor. On a dual processor, or higher, you may get some gain
from running two threads. However, there is a risk that the chunks of
parallel work may be too small, and the cost of synchronization too
high, for a net gain. Also, you may find data contention between the two
processors messes up caching, reducing performance.
Even if you have separate disk drives or a dual processor, I would start
with the simple single thread implementation, and only consider going to
two threads if this turns out to be performance critical relative to the
whole program.
Patricia