A way to track the current block level for instance block-methods, which is completely thread-safe

thread_safe_block_depth.rb

class MyObject
  
  def block_depth=(value)
    Thread.current[:block_depth] = value
  end
  
  def block_depth
    Thread.current[:block_depth] || 0
  end
  
  def track_block_depth(&block)
    self.block_depth += 1
    yield
    ensure
      self.block_depth -= 1
  end
  
  def method1(stuff, &block)
    track_block_depth do
      puts "This is #{stuff}... #{self.block_depth} level deep\n"
      yield
    end
  end
  
  def method2(stuff, &block)
    track_block_depth do
      puts "This is #{stuff}... #{self.block_depth} levels deep\n"
      yield
    end
  end

end

obj = MyObject.new

t1 = Thread.new do
  obj.method1 "something" do
    obj.method2 "something else" do
      puts "hiya\n"
    end
    puts "Back to #{obj.block_depth} level deep\n"
  end
end

t2 = Thread.new do
  obj.method1 "something" do
    obj.method2 "something else" do
      puts "hiya\n"
    end
    puts "Back to #{obj.block_depth} level deep\n"
  end
end

t1.join
t2.join

# => This is something... 1 level deep
# => This is something... 1 level deep
# => This is something else... 2 levels deep
# => This is something else... 2 levels deep
# => hiya
# => hiya
# => Back to 1 level deep
# => Back to 1 level deep