|Perl: the Markov chain saw|
Re^5: question about running a system and a perl function backgroundby BrowserUk (Patriarch)
|on Dec 15, 2004 at 21:01 UTC||Need Help??|
The shared hash %lookfor is initalised with the search terms as the arguments and undef as the values;
In the thread, the keys are used to search the lines of input from the command, and if the key is found, then the line of text in which it is found is assigned to the hash as the value of that key:
When one occurance of each of the search terms has been seen, all the lvalues of %lookfor will have been defined (because they will have had the line they where found in assigned to them), so the test for whether all teh search terms have been located once) is:
That says, "We are done, when the number of defined values in this hash is equal to the number of keys".
Also, had a little trouble understanding what the following means... (what does < do ?)
The shared array @dones is initalised to zeros. One for each thread.
A reference to a different one of the array elements is passed to each thread on creation:
Each thread sets it's element of @dones to 1 as it exits.
The condition of the while modifier to the sleep statement use grep to count the number of elements of @dones that have a true value (1) and compares that with the number of threads (@cmds) started, and sleeps until all the threads are done.
I understood that when the keywords are found, kill 1, $pid immediatly kills the pid for that particular thread, but does it also stop the other 3 threads that are still going on?
Sorry. Your confusion is understandable as that was my 'deliberate omission' :) (I wish!). Basically, I forgot to implement that part of the algorithm and my testcase (such as it is) was insufficuent for me to notice. By way of recompense, here's a modified version with the 'stop the other threads' part implemented, along with a coupe of changes to do the 'stop immediately if you fond this term' bit you wanted.
The problem of getting the search to cease when a given term has been matched, regardless of whether the others have or not, becomes one of deciding how to indicate which of the terms is accorded this special treatment. First how do indicate this on the command line, and then how to indicate if in the hash. Though the former may not be a requirement for your application.
For simplicity, I've opted to use a trailing pling '!' to indicated show stoppers from the command line.
To convey the 'this is a stopper term' to the threads, I'm initialising the value associated with those term(s) in the hash to '1', and the others to 0. It then uses this information to decide whether to set the shared $quitNow flag and stop the other threads.
NOTE: As always, this isn't intended to totally solve the problem, or be fully tested code. Just an example of one way to approach the problem, that is tested in as much as it has appeared to do the right thing a few times :)
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