Question

我不到一周前开始使用Ruby，但已经开始使用了欣赏语言的力量。我正在尝试经典生产者 - 消费者问题，实施为橙树（c.f. http://pine.fm/LearnToProgram/?Chapter=09）。橘子树各生长直到它死亡并且每年产生随机数量的橙子（监制）。只要树上有任何东西，就可以采摘橘子（消费者）。

我在这里遇到两个问题：

以下代码给出了以下异常（无法附加，无选项）：

/Users/Abhijit/Workspace/eclipse/ruby/learn_to_program/orange_tree.rb:84:
warning: instance variable @orange_tree not initialized
/Users/Abhijit/Workspace/eclipse/ruby/learn_to_program/orange_tree.rb:84:in `':

undefined method `age' for nil:NilClass (NoMethodError) from
/Users/Abhijit/Workspace/eclipse/ruby/learn_to_program/orange_tree.rb:45:in `'

我不确定多线程部分是否正确编码。

我有几本书，包括“编程Ruby”和“Ruby编程语言”，但它们都没有包含真正的“生产者 - 消费者问题”。

P.S：为了充分披露，我也在Ruby论坛上发布了这个问题。但是，我已经看到了这里提供的优秀答案和/或建议，并希望我也能得到其中的一些。

require 'thread'

class OrangeTree
GROWTH_PER_YEAR = 1
AGE_TO_START_PRODUCING_ORANGE = 3
AGE_TO_DIE = 7
ORANGE_COUNT_RELATIVE_TO_AGE = 50
def initialize
  @height = 0
  @age = 0
  @orange_count = 0
end

def height
  return @height
end

def age
  return @age
end

def count_the_oranges
  return @orange_count
end

def one_year_passes
  @age += 1
  @height += GROWTH_PER_YEAR
  @orange_count = Math.rand(@age..AGE_TO_DIE) * Math.log(@age) * ORANGE_COUNT_RELATIVE_TO_AGE
end

def pick_an_orange
  if (@age == AGE_TO_DIE)
    puts "Sorry, the Orange tree is dead"
  elsif (@orange_count > 0)
    @orange_count -= 1
    puts "The Orange is delicious"
  else
    puts "Sorry, no Oranges to pick"
  end
end

end

class Worker
  def initialize(mutex, cv, orange_tree)
  @mutex = mutex
  @cv = cv
  @orange_tree = orange_tree
end

def do_some_work
  Thread.new do
    until (@orange_tree.age == OrangeTree.AGE_TO_DIE)
      @mutex.synchronize do
        sleep_time = rand(0..5)
        puts "Orange picker going to sleep for #{sleep_time}"
        sleep(sleep_time)
        puts "Orange picker woke up after sleeping for #{sleep_time}"
        @orange_tree.pick_an_orange
        puts "Orange picker waiting patiently..."
        @cv.wait(@mutex)
      end
    end
  end

  Thread.new do
    until (@orange_tree.age == OrangeTree.AGE_TO_DIE)
      @mutex.synchronize do
        sleep_time = rand(0..5)
        puts "Age increaser going to sleep for #{sleep_time}"
        sleep(sleep_time)
        puts "Age increaser woke up after sleeping for #{sleep_time}"
        @orange_tree.one_year_passes
        puts "Age increaser increased the age"
        @cv.signal
      end
    end
  end
end

Worker.new(Mutex.new, ConditionVariable.new, OrangeTree.new).do_some_work
until (@orange_tree.age == OrangeTree.AGE_TO_DIE)
  # wait for the Threads to finish
end

end

Answer 1

@orange_tree是Worker对象的实例变量，只能从对象内部访问。您试图在“直到”状态下从全局范围访问它，它不存在。有几种方法可以解决它，但这个方法需要的变化最少：

...

orange_tree = OrangeTree.new
Worker.new(Mutex.new, ConditionVariable.new, orange_tree).do_some_work
until (orange_tree.age == OrangeTree::AGE_TO_DIE)
...

您还应该查看Thread#join：http://www.ruby-doc.org/core-1.9.3/Thread.html#method-i-join。它将照顾你的等待。其余的多线程代码在技术上看起来是正确的。我相信你知道，如果这不仅仅是一个练习，你会想让互斥体更精细。正如他们现在所说的那样，两个线程几乎完全相互执行，哪种线程会破坏线程点。

另外，请查看attr_accessor或attr_reader。他们将节省您手动定义OrangeTree#height，age等

的费用

多个加入示例

threads = []

threads << Thread.new do
  ...
end

threads << Threads.new do
  ...
end

threads.each { |thread| thread.join }

Ruby多线程生产者 - 消费者

1 个答案: