ManualResetEvent的简单理解

看了很久的ManualResetEvent，但还是没看明白官方的解释，不妨让我们来看看定义的英文注释，或许更容易理解：

// Summary:
 //     Initializes a new instance of the System.Threading.ManualResetEvent class
 //     with a Boolean value indicating whether to set the initial state to signaled.
 //
 // Parameters:
 //   initialState:
 //     true to set the initial state signaled; false to set the initial state to
 //     nonsignaled.
 [SecuritySafeCritical]
 public ManualResetEvent(bool initialState);
 
 //
 // Summary:
 //     Sets the state of the event to nonsignaled, causing threads to block.
 //
 // Returns:
 //     true if the operation succeeds; otherwise, false.
 [SecuritySafeCritical]
 public bool Reset();
 
 //
 // Summary:
 //     Blocks the current thread until the current System.Threading.WaitHandle receives
 //     a signal, using a 32-bit signed integer to measure the time interval.
 //
 // Parameters:
 //   millisecondsTimeout:
 //     The number of milliseconds to wait, or System.Threading.Timeout.Infinite
 //     (-1) to wait indefinitely.
 //
 // Returns:
 //     true if the current instance receives a signal; otherwise, false.
 //
 // Exceptions:
 //   System.ObjectDisposedException:
 //     The current instance has already been disposed.
 //
 //   System.ArgumentOutOfRangeException:
 //     millisecondsTimeout is a negative number other than -1, which represents
 //     an infinite time-out.
 //
 //   System.Threading.AbandonedMutexException:
 //     The wait completed because a thread exited without releasing a mutex. This
 //     exception is not thrown on Windows 98 or Windows Millennium Edition.
 //
 //   System.InvalidOperationException:
 //     The current instance is a transparent proxy for a System.Threading.WaitHandle
 //     in another application domain.
 public virtual bool WaitOne(int millisecondsTimeout);
 
 //
 // Summary:
 //     Sets the state of the event to signaled, allowing one or more waiting threads
 //     to proceed.
 //
 // Returns:
 //     true if the operation succeeds; otherwise, false.
 [SecuritySafeCritical]
 public bool Set();

总结：

• ManualResetEvent 实例时接收一个Boolean类型的参数来初始化其状态，true表示畅通无阻的状态(signaled)，线程不能阻塞，即使调用WaitOne也不能 阻塞；false表示是可阻塞的状态(nonsignaled)，可以调用WaitOne等方法来阻塞的。这里初始化的只是一个状态。
• Reset方法把 ManualResetEvent 的状态设置为可阻塞的(nonsignaled)，不管之前是什么状态，调用Reset都把状态设置为阻塞的(nonsignaled)。
• WaitOne 阻塞当前线程直到别的线程调用Set方法，只有ManualResetEvent 的状态是可阻塞(nonsignaled)时，WaitOne才能真正的起到作用；