FileSystemWatcher 的问题，你会发现很多关于 FileSystemWatcher 跳过某些事件（未触发所有事件）的文章。基本上，如果你在监视的文件夹中更改了很多文件，其中一些文件将不会被 FileSystemWatcher 处理。FileSystemWatcher正在监视某个文件夹中发生的更改。当文件被更改时（例如文件被创建），FileSystemWatcher会触发相应的事件。事件处理程序可以解压缩文件，读取其内容以确定如何进一步处理它，在数据库日志表中写入记录并将文件移动到另一个文件夹。文件的处理可能需要一些时间。
在此期间，可能会在所监视的文件夹中创建另一个文件。由于FileSystemWatcher的事件处理程序正在处理第一个文件，因此无法处理第二个文件的创建事件。因此，FileSystemWatcher会错过第二个文件。
由于文件处理可能需要一些时间，并且其他文件的创建可能无法被FileSystemWatcher检测到，因此应该将文件处理与文件更改检测分开，并且文件更改检测应该非常短，以便它永远不会错过单个文件更改。文件处理可以分成两个线程：一个用于文件更改检测，另一个用于文件处理。当文件被更改并且被FileSystemWatcher检测到时，适当的事件处理程序应仅读取其路径，将其转发到文件处理线程并关闭本身，以便FileSystemWatcher可以检测到另一个文件更改并使用相同的事件处理程序。处理线程可以花费任意时间来处理该文件。队列用于将文件路径从事件处理程序线程转发到处理线程。
这是经典的生产者-消费者问题。有关生产者-消费者队列的更多信息，请参见此处。
using System;
using System.IO;
using System.Threading;
using System.Collections.Generic;
namespace FileSystemWatcherExample {
class Program {
static void Main(string[] args) {
// If a directory and filter are not specified, exit program
if (args.Length !=2) {
// Display the proper way to call the program
Console.WriteLine("Usage: Watcher.exe \"directory\" \"filter\"");
return;
}
FileProcessor fileProcessor = new FileProcessor();
// Create a new FileSystemWatcher
FileSystemWatcher fileSystemWatcher1 = new FileSystemWatcher();
// Set FileSystemWatcher's properties
fileSystemWatcher1.Path = args[0];
fileSystemWatcher1.Filter = args[1];
fileSystemWatcher1.IncludeSubdirectories = false;
// Add event handlers
fileSystemWatcher1.Created += new System.IO.FileSystemEventHandler(this.fileSystemWatcher1_Created);
// Start to watch
fileSystemWatcher1.EnableRaisingEvents = true;
// Wait for the user to quit the program
Console.WriteLine("Press \'q\' to quit the program.");
while(Console.Read()!='q');
// Turn off FileSystemWatcher
if (fileSystemWatcher1 != null) {
fileSystemWatcher1.EnableRaisingEvents = false;
fileSystemWatcher1.Dispose();
fileSystemWatcher1 = null;
}
// Dispose fileProcessor
if (fileProcessor != null)
fileProcessor.Dispose();
}
// Define the event handler
private void fileSystemWatcher1_Created(object sender, FileSystemEventArgs e) {
// If file is created...
if (e.ChangeType == WatcherChangeTypes.Created) {
// ...enqueue it's file name so it can be processed...
fileProcessor.EnqueueFileName(e.FullPath);
}
// ...and immediately finish event handler
}
}
// File processor class
class FileProcessor : IDisposable {
// Create an AutoResetEvent EventWaitHandle
private EventWaitHandle eventWaitHandle = new AutoResetEvent(false);
private Thread worker;
private readonly object locker = new object();
private Queue<string> fileNamesQueue = new Queue<string>();
public FileProcessor() {
// Create worker thread
worker = new Thread(Work);
// Start worker thread
worker.Start();
}
public void EnqueueFileName(string FileName) {
// Enqueue the file name
// This statement is secured by lock to prevent other thread to mess with queue while enqueuing file name
lock (locker) fileNamesQueue.Enqueue(FileName);
// Signal worker that file name is enqueued and that it can be processed
eventWaitHandle.Set();
}
private void Work() {
while (true) {
string fileName = null;
// Dequeue the file name
lock (locker)
if (fileNamesQueue.Count > 0) {
fileName = fileNamesQueue.Dequeue();
// If file name is null then stop worker thread
if (fileName == null) return;
}
if (fileName != null) {
// Process file
ProcessFile(fileName);
} else {
// No more file names - wait for a signal
eventWaitHandle.WaitOne();
}
}
}
private ProcessFile(string FileName) {
// Maybe it has to wait for file to stop being used by process that created it before it can continue
// Unzip file
// Read its content
// Log file data to database
// Move file to archive folder
}
#region IDisposable Members
public void Dispose() {
// Signal the FileProcessor to exit
EnqueueFileName(null);
// Wait for the FileProcessor's thread to finish
worker.Join();
// Release any OS resources
eventWaitHandle.Close();
}
#endregion
}
}