在 C# 中安全回显 MIDI 数据
作为一个业余项目，我正在实现一个 MIDI 矩阵，以将多个 MIDI 键盘与声源互连。这里的关键要求是将输入端口上接收到的 MIDI 数据回显到选定的输出端口。
创建必要的 P/Invoke 声明和包装器，我注意到 MidiInProc 的 Win32 MIDI 文档指出：“应用程序不应从回调函数内部调用任何多媒体函数，因为这样做可能会导致死锁”。
鉴于从 MidiInProc 中调用 midiOutShortMsg 是不安全的，我当前的解决方案是将 MIDI 数据写入队列并设置一个事件。工作线程等待该事件并调用 midiOutShortMsg。总体思路是这样的：-
static void InputCallback( int hMidiIn, uint wMsg, uint dwInstance, uint dwParam1, uint dwParam2 )
{
if( wMsg == MM_MIM_DATA )
{
data.EnQueue( dwParam1 ); //data is a Queue<uint>
dataReady.Set(); //dataReady is AutoResetEvent
}
}
void ThreadProc
{
while( !_done )
{
dataReady.WaitOne();
midiOutShortMsg( hMidiOut, data.DeQueue() );
}
}
然而，虽然这在测试中运行良好，但在调用 dataReady.Set() 和 InputCallBack 之间似乎存在一个机会之窗> 返回期间抢占可能允许工作线程调用 midiOutShortMsg（尽管在另一个线程中）。
这种方法安全吗？
As a side project, I am implementing a MIDI matrix to interconnect a number of MIDI keyboards with sound sources. The key requirement here is to echo MIDI data received on an input port to a selected output port.
Having created the necessary P/Invoke declarations & wrappers, I notice that the Win32 MIDI documentation for MidiInProc states: "Applications should not call any multimedia functions from inside the callback function, as doing so can cause a deadlock".
Given that it is unsafe to call midiOutShortMsg from within a MidiInProc, my current solution is to write MIDI data to a queue and set an event. A worker thread waits on the event and calls midiOutShortMsg. The general idea is this:-
static void InputCallback( int hMidiIn, uint wMsg, uint dwInstance, uint dwParam1, uint dwParam2 )
{
if( wMsg == MM_MIM_DATA )
{
data.EnQueue( dwParam1 ); //data is a Queue<uint>
dataReady.Set(); //dataReady is AutoResetEvent
}
}
void ThreadProc
{
while( !_done )
{
dataReady.WaitOne();
midiOutShortMsg( hMidiOut, data.DeQueue() );
}
}
However, whilst this has been working fine in testing, there appears to be a window of opportunity between the call to dataReady.Set() and InputCallBack returning during which preemption could allow the worker thread to call midiOutShortMsg (albeit in another thread).
Is this approach safe?
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评论（2）
对我来说看起来很安全：即使您的两个线程同时运行，它仍然只有工作线程可能会阻塞，因此这不会导致您的输入回调死锁。
Looks safe to me: even if your two threads are running at the same time, it's still only the worker thread that might block, so this won't deadlock your input callback.
您的问题可能有点针对 StackOverflow 领域。如果这里没有人回答，请查看：http://groups.google .com/group/mididev?hl=en&lnk=
Your question might be a bit domain-specific for StackOverflow. If no one here answers it, check out: http://groups.google.com/group/mididev?hl=en&lnk=