在Windows操作系统中，事件日志是一种记录系统、应用程序和服务运行状态的重要方式。当需要实时监控事件日志时，如果日志生成速度非常快，使用传统的EventLog.EntryWritten事件来读取日志可能会导致应用程序响应变慢甚至挂起。为了解决这个问题，可以使用EventLogQuery和EventLogReader类来读取最新的事件日志。
以下是实现实时事件日志读取器的步骤和关键点：
首先，需要创建一个EventLogQuery对象，它允许基于创建时间来查询事件日志。然后，使用EventLogReader类来读取这些事件。这种方法可以避免应用程序因频繁触发EventLog.EntryWritten事件而变慢。
RealTimeEventLogReader是一个后台线程，它不会读取在运行之前已经存在于Windows事件日志中的日志。它只会在有新的日志写入时显示日志。
用户可以通过输入日志名称并点击确认按钮来启动实时日志读取器。如果输入的日志名称有效，应用程序将显示一个窗口，用户可以通过启动或停止某些服务来生成日志。
以下是一些关键的代码片段，展示了如何实现实时事件日志读取器：
public EventLogRecord(EventRecord eventdetail)
{
eventID = eventdetail.Id;
detailsXML = eventdetail.ToXml();
taskCategory = eventdetail.Task.Value;
timestamp = eventdetail.TimeCreated.Value;
source = eventdetail.ProviderName;
level = (LogLevel)eventdetail.Level.Value;
levelString = eventdetail.LevelDisplayName;
logName = eventdetail.LogName;
eventData = GetEventData(eventdetail);
}
public delegate void AddRecordDelegate(EventLogRecord record);
public AddRecordDelegate AddRecord;
private Thread readerThread = null;
private DateTime _lastReadTime = DateTime.UtcNow;
private const string TimeFormatString = "yyyy-MM-ddTHH:mm:ss.fffffff00K";
private const string EventReaderQuery = "*[System/TimeCreated/@SystemTime >='{0}']";
private void ReadLogs()
{
while (!Stop)
{
double elapsedTimeSincePreviousRead = (DateTime.UtcNow - _lastReadTime).TotalSeconds;
DateTime timeSpanToReadEvents = DateTime.UtcNow.AddSeconds(-elapsedTimeSincePreviousRead);
string strTimeSpanToReadEvents = timeSpanToReadEvents.ToString(TimeFormatString, CultureInfo.InvariantCulture);
string query = string.Format(EventReaderQuery, strTimeSpanToReadEvents);
int readEventCount = 0;
EventLogQuery eventsQuery = new EventLogQuery(LogName, PathType.LogName, query) { ReverseDirection = true };
EventLogReader logReader = new EventLogReader(eventsQuery);
_lastReadTime = DateTime.UtcNow;
for (EventRecord eventdetail = logReader.ReadEvent(); eventdetail != null; eventdetail = logReader.ReadEvent())
{
byte[] bytes = null;
if (eventdetail.Properties.Count >= 2)
{
bytes = (byte[])eventdetail.Properties[eventdetail.Properties.Count - 1].Value;
}
EventLogRecord record = new EventLogRecord(eventdetail);
if (parser.IsValid(temporaryRecord))
{
PostDetail(record);
}
if (++readEventCount >= LogLimit)
{
break;
}
}
Thread.Sleep(ReadInterval);
}
}
private void PostDetail(params EventLogRecord[] records)
{
if (AddRecord != null && records != null)
{
foreach (EventLogRecord record in records)
{
if (record != null)
{
AddRecord.BeginInvoke((EventLogRecord)record.Clone(), null, null);
}
}
}
}
private void AddRecord(EventLogRecord record)
{
eventLogRecordList.Add(record);
toolStripStatusLabelNumCount.Text = eventLogRecordList.Count.ToString();
toolStripStatusLabelStatusString.Text = "Started";
if (eventLogRecordList.Count >= reader.LogLimit)
{
eventLogRecordList.RemoveAt(0);
}
gvLogs.FirstDisplayedScrollingRowIndex = gvLogs.RowCount - 1;
}