作者：liuc | 来源：互联网 | 2023-05-18 09:02
一、这里主要说明2种异步写入文件的方法：1）异步编程模型API转为Task——使用Task.Factory.FromAsync方法2）对于StreamWriter使用WriteAs
一、这里主要说明2种异步写入文件的方法：
1）异步编程模型API转为Task——使用Task.Factory.FromAsync方法
2）对于StreamWriter使用WriteAsync方法
请记得对stream对象使用FileOptions.Asynchronous选项！
首先来看一下准备函数：
CreateFileContent是用来随机生成要写入的内容（字符串形式）；
SumFileContent
- static string CreateFileContent()
- {
- var sb = new StringBuilder();
- for (int i = 0; i < 100000; i++)
- {
- sb.AppendFormat("{0}", new Random(i).Next(0, 99999));
- sb.AppendLine();
- }
- return sb.ToString();
- }
-
- async static Task<long> SumFileContent(string fileName)
- {
- using (var stream = new FileStream(fileName, FileMode.Open, FileAccess.Read,FileShare.None, BUFFER_SIZE, FileOptions.Asynchronous))
- using (var sr = new StreamReader(stream))
- {
- long sum = 0;
- while (sr.Peek() > -1)
- {
- string line = await sr.ReadLineAsync();
- sum += long.Parse(line);
- }
-
- return sum;
- }
- }
-
- static Task SimulateAsynchronousDelete(string fileName)
- {
- return Task.Run(() => File.Delete(fileName));
- }
1）Task.Factory.FromAsync方法
- using (var stream = new FileStream("test2.txt", FileMode.Create, FileAccess.ReadWrite, FileShare.None, BUFFER_SIZE, FileOptions.Asynchronous))
- {
- Console.WriteLine("2. Uses I/O Threads: {0}", stream.IsAsync);
- byte[] buffer = Encoding.UTF8.GetBytes(CreateFileContent());
- var writeTask = Task.Factory.FromAsync(stream.BeginWrite, stream.EndWrite, buffer, 0, buffer.Length, null);
-
- await writeTask;
- }
2）StreamWriter.WriteAsync方法
- using (var stream = File.Create("test3.txt", BUFFER_SIZE, FileOptions.Asynchronous))
- using (var sw = new StreamWriter(stream))
- {
- Console.WriteLine("3. Uses I/O Threads: {0}", stream.IsAsync);
- await sw.WriteAsync(CreateFileContent());
- }
二、异步从文件中读取内容（四个Task来数字数，WhenAll后再相加）
- Console.WriteLine("Starting parsing files in parallel");
-
- Task<long>[] readTasks = new Task<long>[4];
- for (int i = 0; i < 4; i++)
- {
- readTasks[i] = SumFileContent(string.Format("test{0}.txt", i + 1));
- }
-
- long[] sums = await Task.WhenAll(readTasks);
-
- Console.WriteLine("Sum in all files: {0}", sums.Sum());
三、模拟异步删除（因为API中没有异步删除）
- Console.WriteLine("Deleting files...");
-
- Task[] deleteTasks = new Task[4];
- for (int i = 0; i < 4; i++)
- {
- string fileName = string.Format("test{0}.txt", i + 1);
- deleteTasks[i] = SimulateAsynchronousDelete(fileName);
- }
-
- await Task.WhenAll(deleteTasks);
-
- Console.WriteLine("Deleting complete.");
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