13.1.4 实现会合点并拦截返回值

t1 = Thread.new { do_something_long() }
do_something_brief()
t1.join              # Wait for t1

meaning_of_life = Thread.new do
puts "The answer is..."
sleep 10
puts 42
end
sleep 9
meaning_of_life.join  

Thread.list.each { |t| t.join if t != Thread.main } 

thr = Thread.new { sleep 1; Thread.main.join }
thr.join         # Deadlock results!   

max = 10000
thr = Thread.new do
sum = 0
1.upto(max) { |i| sum += i }
sum
end
guess = (max*(max+1))/2
print "Formula is "
if guess == thr.value
puts "right."
else
puts "wrong."
end