我遇到了FileSystemWatcher的问题。我在Windows服务中使用它来监视某些文件夹，并且在复制文件时，它使用SSIS包来处理该文件。一切正常，但FileWatcher每隔一段时间就会获取同一个文件并在infinate循环中多次触发Created事件。以下代码的工作原理如下：
首先，这个方法由windows服务调用并创建一个观察者：
private void CreateFileWatcherEvent(SSISPackageSetting packageSettings)
{
// Create a new FileSystemWatcher and set its properties.
FileSystemWatcher watcher = new FileSystemWatcher();
watcher.IncludeSubdirectories = false;
watcher.Path = packageSettings.FileWatchPath;
/* Watch for changes in LastAccess and LastWrite times, and
the renaming of files or directories. */
watcher.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite
| NotifyFilters.FileName | NotifyFilters.DirectoryName | NotifyFilters.Size;
//Watch for all files
watcher.Filter = "*.*";
watcher.Created += (s, e) => FileCreated(e, packageSettings);
// Begin watching.
watcher.EnableRaisingEvents = true;
}
接下来，Watcher.Created事件看起来像这样：
private void FileCreated(FileSystemEventArgs e, SSISPackageSetting packageSettings)
{
//Bunch of other code not important to the issue
ProcessFile(packageSettings, e.FullPath, fileExtension);
}
ProcessFile方法如下所示：
private void ProcessFile(SSISPackageSetting packageSetting,string Filename,string fileExtension)
{
//COMPLETE A BUNCH OF SSIS TASKS TO PROCESS THE FILE
//NOW WE NEED TO CREATE THE OUTPUT FILE SO THAT SSIS CAN WRITE TO IT
string errorOutPutfileName = packageSetting.ImportFailurePath + @"\FailedRows" + System.DateTime.Now.ToFileTime() + packageSetting.ErrorRowsFileExtension;
File.Create(errorOutPutfileName).Close();
MoveFileToSuccessPath(Filename, packageSetting);
}
最后，MoveFile方法如下所示：
private void MoveFileToSuccessPath(string filename, SSISPackageSetting ssisPackage)
{
try
{
string newFilename = MakeFilenameUnique(filename);
System.IO.File.Move(filename, ssisPackage.ArchivePath.EndsWith("\\") ? ssisPackage.ArchivePath + newFilename : ssisPackage.ArchivePath + "\\" + newFilename);
}
catch (Exception ex)
{
SaveToApplicationLog(string.Format
("Error ocurred while moving a file to the success path. Filename {0}. Archive Path {1}. Error {2}", filename, ssisPackage.ArchivePath,ex.ToString()), EventLogEntryType.Error);
}
}
所以在那里，我们进入一个无限循环，FileWatcher继续拾取同一个文件。任何人都有任何想法？这是随机和间歇发生的。
答案 0 :(得分：1)
使用FileSystemWatcher时，我倾向于使用字典将文件添加到通知事件触发时。然后我有一个单独的线程使用一个计时器，当它们超过几秒钟时，从这个集合中挑选文件，大约5秒钟。
如果我的处理也可能改变上次访问时间，我也会观察，那么我也实现了一个校验和，我将其保存在字典中，同时保存每个文件的文件名和最后处理时间，并使用它来抑制它的触发连续多次。您不必使用昂贵的计算，我使用md5甚至crc32 - 您只是试图阻止多个通知。
修改
此示例代码特定于情境，并且您可能需要更改许多假设。它没有列出你所有的代码，只是像你需要添加的那些代码一样：
// So, first thing to do is add a dictionary to store file info:
internal class FileWatchInfo
{
public DateTime LatestTime { get; set; }
public bool IsProcessing { get; set; }
public string FullName { get; set; }
public string Checksum { get; set; }
}
SortedDictionary<string, FileWatchInfo> fileInfos = new SortedDictionary<string, FileWatchInfo>();
private readonly object SyncRoot = new object();
// Now, when you set up the watcher, also set up a [`Timer`][1] to monitor that dictionary.
CreateFileWatcherEvent(new SSISPackageSetting{ FileWatchPath = "H:\\test"});
int processFilesInMilliseconds = 5000;
Timer timer = new Timer(ProcessFiles, null, processFilesInMilliseconds, processFilesInMilliseconds);
// In FileCreated, don't process the file but add it to a list
private void FileCreated(FileSystemEventArgs e) {
var finf = new FileInfo(e.FullPath);
DateTime latest = finf.LastAccessTimeUtc > finf.LastWriteTimeUtc
? finf.LastAccessTimeUtc : finf.LastWriteTimeUtc;
latest = latest > finf.CreationTimeUtc ? latest : finf.CreationTimeUtc;
// Beware of issues if other code sets the file times to crazy times in the past/future
lock (SyncRoot) {
// You need to work out what to do if you actually need to add this file again (i.e. someone
// has edited it in the 5 seconds since it was created, and the time it took you to process it)
if (!this.fileInfos.ContainsKey(e.FullPath)) {
FileWatchInfo info = new FileWatchInfo {
FullName = e.FullPath,
LatestTime = latest,
IsProcessing = false, Processed = false,
Checksum = null
};
this.fileInfos.Add(e.FullPath, info);
}
}
}
最后，这是现在的处理方法
private void ProcessFiles(object state) {
FileWatchInfo toProcess = null;
List<string> toRemove = new List<string>();
lock (this.SyncRoot) {
foreach (var info in this.fileInfos) {
// You may want to sort your list by latest to avoid files being left in the queue for a long time
if (info.Value.Checksum == null) {
// If this fires the watcher, it doesn't matter, but beware of big files,
// which may mean you need to move this outside the lock
string md5Value;
using (var md5 = MD5.Create()) {
using (var stream = File.OpenRead(info.Value.FullName)) {
info.Value.Checksum =
BitConverter.ToString(md5.ComputeHash(stream)).Replace("-", "").ToLower();
}
}
}
// Data store (myFileInfoStore) is code I haven't included - use a Dictionary which you remove files from
// after a few minutes, or a permanent database to store file checksums
if ((info.Value.Processed && info.Value.ProcessedTime.AddSeconds(5) < DateTime.UtcNow)
|| myFileInfoStore.GetFileInfo(info.Value.FullName).Checksum == info.Value.Checksum) {
toRemove.Add(info.Key);
}
else if (!info.Value.Processed && !info.Value.IsProcessing
&& info.Value.LatestTime.AddSeconds(5) < DateTime.UtcNow) {
info.Value.IsProcessing = true;
toProcess = info.Value;
// This processes one file at a time, you could equally add a bunch to a list for parallel processing
break;
}
}
foreach (var filePath in toRemove) {
this.fileInfos.Remove(filePath);
}
}
if (toProcess != null)
{
ProcessFile(packageSettings, toProcess.FullName, new FileInfo(toProcess.FullName).Extension);
}
}
最后，ProcessFile需要处理您的文件，然后在完成锁定后，将fileInfos字典中的信息标记为Processed，设置ProcessedTime，然后退出锁并移动文件。如果校验和在可接受的时间过后发生变化，您还需要更新校验和。
提供完整的样本非常困难，因为我对你的情况一无所知，但这是我使用的一般模式。您需要考虑文件速率，更新频率等等。您可以将时间间隔缩短到亚秒而不是5秒，仍然可以。