//The item is expired, call the "Refresh" action of this item to get a refresh value
//1. If there's not enough worker threads, the dispatching thread will wait until the below 2 conditions happend:
//(1). There is worker threads available
//(2). There is user event comming (Add/Remove etc.)
//2. If there's at least one worker thread, the dispatching thread will schedule the "Refresh" action in one worker thread
//after the worker thread end to refresh the cache item, it will release the worker thread resource, and notify the
//dispatching thread, so that other expired cache items wait for refresh worker thread can do their refresh job
private bool RefreshExpiredCache(SchedulerKey sk, CacheItem ci)
{
//Refresh the expired item now, but firstly we should get a token
if (Interlocked.Decrement(ref m_availRefreshThreadCount) < 0)
{
//Got an invalid token, return it
Interlocked.Increment(ref m_availRefreshThreadCount);
//No available refresh thread now, wait for one
LogManager.Info("CacheManager:ProcessTimerEvents", string.Format("Begin to wait for refreshing thread token with key [{0}]", sk.Key));
m_waitHandle.WaitOne();
//Either there's an user event comming or a refresh thread token is available
LogManager.Info("CacheManager:ProcessTimerEvents", string.Format("End to wait for refreshing thread token with key [{0}]", sk.Key));
//No need to wait again, start a new loop
return false;
}
//Save the last expiration time
ci.LastExpirationInfo.LastExpiration = ci.NextExpirationTime;
//Update the next expiration time for next schedule
ci.NextExpirationTime = ci.Expiration.NextExpiration(ci.LastExpirationInfo);
//Validation
TimeSpan ts = ci.NextExpirationTime - ci.LastExpirationInfo.LastExpiration;
if (ts.TotalMilliseconds < MIN_WAIT_TIME)
{
LogManager.Warn("CacheManager:ProcessTimerEvents", "Too short time interval, ts=" + ts.TotalMilliseconds);
//wait 3s
ci.NextExpirationTime = ci.LastExpirationInfo.LastExpiration.AddMilliseconds(3000);
}
//Re-schedule again
m_heap.Remove(sk);
m_heap.Add(new SchedulerKey(ci.NextExpirationTime, sk.Key), DUMMY);
//Fire the refresh action
Task.Factory.StartNew(() =>
{
try
{
ci.RefreshAsync();
//Release the token
Interlocked.Increment(ref m_availRefreshThreadCount);
//And notify the listeners
m_waitHandle.Set();
}
catch (Exception ex)
{
LogManager.Error(string.Format("Task for key [{0}] exception", ci.Key), ex);
}
});
return true;
}