Question

可能重复：
Does ruby have the Java equivalent of synchronize keyword?

在Java中，我们可以通过在函数定义中使用'synchronized'关键字来使方法“同步”。

我们如何在Ruby中做到这一点？

Answer 1

Ruby中不存在Synchronize关键字。或者，只需将方法调用包装到Mutex（即锁定的奇特单词）。

为该类创建新的共享互斥锁（每个人都必须使用相同的互斥锁（锁）来访问相同的变量）：

NUM_THREADS = 4

class Foo
  def initialize
    @my_mutex = Mutex.new
    @my_val = 0 # should be private
  end

  def synchronize(&block)
    # to see what it does without the mutex in this example:
    # 1) comment this line
    @my_mutex.synchronize(&block)
    # 2) uncomment this line
    # yield
  end

  def current_value
    synchronize do
      @my_val
    end
  end

  def modify
    # the value should be 0 before and 0 after, if the Mutex is used correctly
    synchronize do
      @my_val += 1
      sleep 0.25
      @my_val -= 1
      sleep 0.25
    end
  end
end

foo = Foo.new

threads = []

# spawn N threads, all trying to change the value
threads += (1..NUM_THREADS).map { |i|
  Thread.new {
    puts "thread [##{i}]: modifying"
    foo.modify
  }
}

# spawn checking thread
threads << Thread.new {
  # print the value twice as fast as the other threads are changing it, so we are more likely to stumble upon wrong state
  (NUM_THREADS * 2).times {
    puts "thread [check]: checking..."
    raise if foo.current_value != 0 # locking failed, crash
    sleep 0.25
  }
}

threads.map { |t| t.join } # wait for all threads

puts "even though it took a while longer, it didn't crash, everyone is happy, managers didn't fire me... it worked!"

请参阅http://apidock.com/ruby/Mutex

由于所有这些锁定，程序运行时间更长。速度取决于您的ruby实现（例如绿色线程，本机线程......）和核心数量。如果您在上面的示例中禁用了互斥锁，程序会立即崩溃，因为检查线程中有加强保护。请注意，检查线程也必须使用互斥锁，否则它仍然能够读取其他线程在更改过程中的值。即每个人都必须使用相同的互斥锁来访问该变量。

为了解决缺少synchronized关键字的问题，我定义了方法synchronize，该方法使用了定义的Mutex类。

Ruby中并发的同步方法

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