流程是: User Interface 需要query資料 >> producer 就produce一個delegate(就是c++ 的function pointer) >> 一大堆的query(其實是fucntion), 就由consumer來執行 >> 等所有有關的query都做完, 就invoke main thread(interface的thread) 的有關control refresh一下, 讓它顯示query了回來的資料
e.g. 有一個label要顯示用戶名稱
labelA.Text = queryUserName(userId, labelA);
public static string queryUserName(uint id, Control control)
{
QueryFunction threadStart = delegate { StaticRes.queryUserNameThread(id, control); };
Program.g_QueryThread.Enqueue(threadStart);
return "Querying User Name...";
}
StaticRes.queryUserNameThread 就是雖要時間較長, 用來query資料的function
以下是class QueryThread的implementation:
public delegate void QueryFunction();
/// <summary>
/// Act as a consumer to the queries produced by the DataGridViewCustomCell
/// </summary>
public class QueryThread
{
private struct QueueItem
{
public Delegate _target;
public UInt64 _id;
public QueueItem(Delegate target, UInt64 id)
{
_target = target;
_id = id;
}
}
private Object _syncEvents = new Object();
private Queue<QueueItem> _queryQueue = new Queue<QueueItem>();
private EventWaitHandle _waitHandle = new EventWaitHandle(false, EventResetMode.AutoReset);
Producer queryProducer;
Consumer queryConsumer;
public QueryThread()
{
queryProducer = new Producer(_queryQueue, _syncEvents, _waitHandle);
queryConsumer = new Consumer(_queryQueue, _syncEvents);
Thread producerThread = new Thread(queryProducer.ThreadRun);
Thread consumerThread = new Thread(queryConsumer.ThreadRun);
producerThread.IsBackground = true;
consumerThread.IsBackground = true;
producerThread.Start();
consumerThread.Start();
}
public void Enqueue(Delegate item, UInt64 id)
{
QueueItem queueItem = new QueueItem(item, id);
_queryQueue.Enqueue(queueItem);
_waitHandle.Set();
}
}
按下來就是producer 跟consumer thread
producer主要是fire event 使consumer thread 開始digest那些query
consumer就是執行enqueue了的query function
class Producer
{
private readonly Queue<QueueItem> _queue;
private Object _sync;
private EventWaitHandle _handle;
public Producer(Queue<QueueItem> q, Object sync, EventWaitHandle waitHandle)
{
_queue = q;
_sync = sync;
_handle = waitHandle;
}
public void ThreadRun()
{
lock (_sync)
{
while (true)
{
//wait until item is enqueued
_handle.WaitOne();
//enqueued, tell worker thread
if (_queue.Count > 0)
{
Monitor.Pulse(_sync);
Monitor.Wait(_sync,0);
}
}
}
}
}
class Consumer
{
private readonly Queue<QueueItem> _queue;
private Object _sync;
public Consumer(Queue<QueueItem> q, Object sync)
{
_queue = q;
_sync = sync;
}
public void ThreadRun()
{
lock (_sync)
{
Delegate query;
while (true)
{
while (_queue.Count == 0)
{
if (Program.g_CustomDialog.Visible == true)
{
Program.g_CustomDialog.DialogResult = DialogResult.OK;
}
Monitor.Wait(_sync);
}
QueueItem item = _queue.Dequeue();
query = item._target;
query.DynamicInvoke(null);
}
}
}
}
後來有人在stackoverflow上說 lock後的 while(true) loop 會容易引致deadlock
由於我的threading implementation比較簡單, 就不作改動了, 下次記緊就好
msdn上對c# threading的教學: How to: Synchronize a Producer and a Consumer Thread
但不要跟他的implementation, 看一看這裡
