Hi guys,
I’d be grateful if someone could take a look at the following two test
cases I made after noticing some strange behavior with ruby threads. I
think the
code speaks clearer than I could, but in essence if you create a lot
of threads from the same block all reading from a single array, things
go wierd. It is almost as if variables get mixed up between the
threads. I am fairly sure this is not expected behavior… If I make
the threads as part of a class, this doesn’t seem to happen.
The first does as you’d expect and never terminates. The second
invariably stops after a few thousand iterations when my exception
gets raised.
I hope I am not wasting your time and have overlooked some glaringly
obvious details about threads, but I am banging my head on the wall
here 
Cheers,
Philip
################################ PROGRAM 1: WORKS, NEVER TERMINATES
require ‘thread’
require ‘digest/md5’
A little class that takes references to two arrays in its constructor
then starts a thread which compares random elements from the two and
throws an exception if they are ever different.
class Tester
def initialize (arrayA, arrayB)
@arrayA = arrayA
@arrayB = arrayB
Thread.start {mainloop}
end
def mainloop
testThread = Thread.new do
while true
i = rand(9)
if (@arrayA[i] != @arrayB[i])
raise Exception.new(“Threading Fuckup”)
end
end
end
end
end
a = []
b = []
Fill an array with 10 random strings, and mirror this
in another identical array.
for i in (0…9)
a[i] = Digest::MD5.hexdigest(rand(1000).to_s).to_s
b[i] = a[i]
end
print “Starting threads…\n”
Thread.abort_on_exception = true
Start 100 threads comparing the elements in the array
for x in (0…100)
Tester.new(a,b)
end
print “And we’re off”
And spin forever
while true do
end
######################################## PROGRAM 2: DOESNT WORK,
TERMINATES
require ‘thread’
require ‘digest/md5’
a = []
b = []
Fill two identical arrays full of 10 random strings
for i in (0…9)
a[i] = Digest::MD5.hexdigest(rand(1000).to_s).to_s
b[i] = a[i]
end
print “Starting threads\n”
Thread.abort_on_exception = true
Start a hundred threads reading items from the two arrays and
comparing them
for x in (0…100)
testThread = Thread.new do
while true
i = rand(9)
if (a[i] != b[i])
raise Exception.new(“Threading Broke”)
end
end
end
end
print “And we’re off”
Spin forever (or at least until an Exception gets thrown)
while true do
end
