Detect number of IDLE processors ruby - ruby

Question

I work on shared linux machines with between 4 and 24 cores. To make best use of them, I use the following code to detect the number of processors from my ruby scripts:
return `cat /proc/cpuinfo | grep processor | wc -l`.to_i
(perhaps there is a pure-ruby way of doing this?)
But sometimes a colleague is using six or eight of the 24 cores. (as seen via top). How can I get an estimate of the number of currently unused processors that I can use without making anyone upset?
Thanks!

Answer 1

You can use the data in the /proc filesystem to get CPU affinity info for running processes. The following should give you the number of CPUs currently in use (Note: I don't have a Linux or Ruby box handy so this code is untested, but you can get the idea):
def processors_in_use
procs=[]
Dir.glob("/proc/*/stat") {|filename|
next if File.directory?(filename)
this_proc=[]
File.open(filename) {|file| this_proc = file.gets.split.values_at(2,38)}
procs << this_proc[1].to_i if this_proc[0]=="R"
}
procs.uniq.length
end
def num_processors
IO.readlines("/proc/cpuinfo").delete_if{|x| x.index("processor")==nil}.length
end
def num_free_processors
num_processors - processors_in_use
end
def estimate_free_cpus(count, waittime)
results=[]
count.times {
results << num_free_processors
sleep(waittime)
}
sum=0
results.each {|x| sum += x}
(sum.to_f / results.length).round
end
Edit: I verified that the above code works (I was using Ruby 1.9)

Answer 2

inspired by bta's reply, this is what i'm using:
private
def YWSystemTools.numberOfActiveProcessors # internal
processorForProcs = []
processFiles = Dir.glob("/proc/*/stat")
raise IOError, 'Cannot find /proc/*/stat files. Are you sure this is a linux machine?' if processFiles.empty?
processFiles.each do |filename|
next if File.directory?(filename) # because /proc/net/stat is a directory
next if !File.exists?(filename) # may have disappeared in the meantime
this_proc = []
File.open(filename) { |file| this_proc = file.gets.split.values_at(2,38) }
processorForProcs << this_proc[1].to_i if this_proc[0]=="R"
end
processorsInUse = processorForProcs.uniq
return(processorsInUse.length)
end
public
def YWSystemTools.numberOfAvailableProcessors
numberOfAttempts = 5
$log.info("Will determine number of available processors. Wait #{numberOfAttempts.to_s} seconds.")
#we estimate 5 times because of local fluctuations in procesor use. Keep minimum.
estimationsOfNumberOfActiveProcessors = []
numberOfAttempts.times do
estimationsOfNumberOfActiveProcessors << YWSystemTools.numberOfActiveProcessors
sleep(1)
end
numberOfActiveProcessors = estimationsOfNumberOfActiveProcessors.min
numberOfTotalProcessors = number_of_processors()
raise IOError, '!! # active Processors > # processors' if numberOfActiveProcessors > numberOfTotalProcessors
numberOfAvailableProcessors = numberOfTotalProcessors - numberOfActiveProcessors
$log.info("#{numberOfAvailableProcessors} out of #{numberOfTotalProcessors} are available!")
return(numberOfAvailableProcessors)
end