How can I modify this method to call it asynchronously?
private void Write(string fileName, data)
{
File.WriteAllText(fileName, data);
}
Look into FileStream.WriteAsync (Note you have to use the proper overload which takes a bool indicating if it should run async:)
public async Task WriteAsync(string data)
{
var buffer = Encoding.UTF8.GetBytes(data);
using (var fs = new FileStream(#"File", FileMode.OpenOrCreate,
FileAccess.Write, FileShare.None, buffer.Length, true))
{
await fs.WriteAsync(buffer, 0, buffer.Length);
}
}
Edit
If you want to use your string data and avoid the transformation to a byte[], you can use the more abstracted and less verbose StreamWriter.WriteAsync overload which accepts a string:
public async Task WriteAsync(string data)
{
using (var sw = new StreamWriter(#"FileLocation"))
{
await sw.WriteAsync(data);
}
}
With .NetCore 2.0 you can just use File.WriteAllTextAsync
Related
Using C# 10 I am creating Stream extensions to get content into a String or Byte array.
Something similar to File.ReadAllTextAsync in Microsoft's Net 6.
public static async Task<string> ReadAllTextAsync(this Stream stream). {
string result;
using (var reader = new StreamReader(stream)) {
result = await reader.ReadToEndAsync().ConfigureAwait(false);
}
return result;
}
public static async Task<byte[]> ReadAllBytesAsync(this Stream stream) {
using (var content = new MemoryStream()) {
var buffer = new byte[4096];
int read = await stream.ReadAsync(buffer, 0, 4096).ConfigureAwait(false);
while (read > 0) {
content.Write(buffer, 0, read);
read = await stream.ReadAsync(buffer, 0, 4096).ConfigureAwait(false);
}
return content.ToArray();
}
}
public static async Task<List<string>> ReadAllLinesAsync(this Stream stream) {
var lines = new List<string>();
using (var reader = new StreamReader(stream)) {
string line;
while ((line = await reader.ReadLineAsync().ConfigureAwait(false)) != null) {
lines.Add(line);
}
}
return lines;
}
Is there a better way to do this?
I am not sure about the ConfigureAwait(false) that I picked on some code online.
A better alternative for the ReadAllBytesAsync is
public static async Task<byte[]> ReadAllBytesAsync(this Stream stream)
{
switch (stream)
{
case MemoryStream mem:
return mem.ToArray();
default:
using var m = new MemoryStream();
await stream.CopyToAsync(m);
return mem.ToArray();
}
}
For the ReadAllLinesAsync, the async stream in C# 8 can make the code cleaner:
public IAsyncEnumerable<string> ReadAllLinesAsync(this Stream stream)
{
using var reader = new StreamReader(stream)
while (await reader.ReadLineAsync() is { } line)
{
yield return line;
}
}
notice that the empty brace { } here is actually a property pattern that is only available after C# 8, it checks whether reader.ReadLineAsync() is null, if it's not, assign it to the line variable.
Usage:
var lines = await stream.ReadAllLinesAsync();
await foreach (var line in lines)
{
// write your own logic here
}
P.S.:
The ConfigureAwait(false) is kinda useless if your app is single-threaded like console apps, it instructs the awaiter not to capture the SynchronizationContext and let continuation run on the thread that runs the await statement, this method is useful when you're writing a library or SDK, since your user may use your library in a GUI application, and the combination of block waiting such as calling Task.Wait() and the capturing of SynchronizationContext often leads to deadlock, and ConfigureAwait(false) solves this. For detail explanation see ConfigureAwait FAQ
In my current code I have a method like this to read data from a device (pseudo code):
public async Task<string> ReadAllDataFromDevice()
{
var buffer = "";
using (var device = new Device())
{
while(device.HasMoreData)
{
buffer += await device.ReadLineAsync();
}
}
return buffer;
}
I then want to send all that data via the network to some receiver. The amount of data can be really large. So clearly the above design is not very memory-efficient since it requires to read all the data before I can start sending it to the network socket.
So what I'd like to have is a function that returns a stream instead. Something like this:
public async Task<Stream> ReadAllDataFromDevice()
{
var stream = new MemoryStream();
using (var device = new Device())
using (var streamWriter = new StreamWriter(stream, new UTF8Encoding(), 512, true))
{
while(device.HasMoreData)
{
var line = await device.ReadLineAsync();
await streamWriter.WriteLineAsync(line);
}
await streamWriter.FlushAsync();
}
return stream;
}
This returns a stream but it clearly does not solve my problem, because the stream is returned only after all the data has been read from the device.
So I came up with this:
public Stream ReadAllDataFromDevice()
{
var stream = new MemoryStream();
Task.Run(async () => {
using (var device = new Device())
using (var streamWriter = new StreamWriter(stream, new UTF8Encoding(), 512, true))
{
while(device.HasMoreData)
{
var line = await device.ReadLineAsync();
await streamWriter.WriteLineAsync(line);
}
await streamWriter.FlushAsync();
}
});
return stream;
}
Is this a good design? I'm especially concerned about thread-safety, lifetime of the stream object used in the lambda, and exception handling.
Or is there a better pattern for this kind of problem?
Edit
Actually I just came up with another design that looks much cleaner to me. Instead of having the ReadAllDataFromDevice() function returning a stream, I let the consumer of the data provide the stream, like this:
public async Task ReadAllDataFromDevice(Stream stream)
{
using (var device = new Device())
using (var streamWriter = new StreamWriter(stream, new UTF8Encoding(), 512, true))
{
while(device.HasMoreData)
{
var line = await device.ReadLineAsync();
await streamWriter.WriteLineAsync(line);
}
await streamWriter.FlushAsync();
}
}
This is the design I'm using now:
public async Task ReadAllDataFromDevice(Func<Stream, Task> readCallback)
{
using (var device = new Device())
{
await device.Initialize();
using (var stream = new DeviceStream(device))
{
await readCallback(stream);
}
}
}
The line-by-line device access is encapsulated in the custom DeviceStream class (not shown here).
The consumer of the data would look something like this:
await ReadAllDataFromDevice(async stream => {
using (var streamReader(stream))
{
var data = await streamReader.ReadToEndAsync();
// do something with data
}
});
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I started to learn about async programming and I stumbled across this problem. I call these functions over an Dispatcher.BeginInvoke.
I'm expecting to get file content form ReadText method, but all I get back is "System.Threading.Tasks.Task`1[System.String]"
So question is what's wrong with my code and which line should I fix?
Sadly I can't figure out where my problem is because I am looking at this peace of code for quite some time now.
I thought because I get back the time of the object and not the object itself that my ReadText method is wrong, but I don't see where. It seems there is something wrong with my part below the Stringbuilder or the way I made these methods async.
If you wonder why I used two methods is to get known with await and calling async Task methods. I also tried making the method a Tast method but that only resulted in even more problems.
Thanks for your help in advance.
public async void ReadFile()
{
string filePath = #"SampleFile.txt";
if (File.Exists(filePath) == false)
{
MessageBox.Show(filePath + " not found", "File Error", MessageBoxButton.OK);
}
else
{
try
{
string text = await ReadText(filePath);
txtContents.Text = text;
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
}
}
private async Task<string> ReadText(string filePath)
{
Task Readfile = Task.Run(() =>
{
using (FileStream sourceStream = new FileStream(filePath,
FileMode.Open, FileAccess.Read, FileShare.Read,
bufferSize: 4096, useAsync: true))
{
StringBuilder sb = new StringBuilder();
byte[] buffer = new byte[0x1000];
int numRead;
while ((numRead = sourceStream.Read(buffer, 0, buffer.Length)) != 0)
{
string text = Encoding.Unicode.GetString(buffer, 0, numRead);
sb.Append(text);
}
return sb.ToString();
}
}
);
await Readfile;
return Readfile.ToString();
}
You are returning a string, so make Readfile a Task<string>:
Task<string> Readfile = Task.Run<string>( ... )
Then you want to return Readfile.Result;, not Readfile.ToString();
But you can write this simpler:
return await Readfile;
or even:
return await Task.Run<string>( ... )
You don't need to use Task.Run for reading from the stream, there is convenient method ReadAsync that you can await:
public async Task ReadFile() {
string filePath = #"SampleFile.txt";
if (File.Exists(filePath) == false) {
MessageBox.Show(filePath + " not found", "File Error", MessageBoxButton.OK);
} else {
try {
string text = await ReadText(filePath);
txtContents.Text = text;
} catch (Exception ex) {
Debug.WriteLine(ex.Message);
}
}
}
private async Task<string> ReadText(string filePath) {
using (FileStream sourceStream = new FileStream(filePath,
FileMode.Open, FileAccess.Read, FileShare.Read,
bufferSize: 4096, useAsync: true)) {
StringBuilder sb = new StringBuilder();
byte[] buffer = new byte[0x1000];
int numRead;
while ((numRead = await sourceStream.ReadAsync(buffer, 0, buffer.Length)) != 0) {
string text = Encoding.Unicode.GetString(buffer, 0, numRead);
sb.Append(text);
}
return sb.ToString();
}
}
Also avoid async void is not recommended, try to avoid that.Async void methods have different error-handling semantics. When an exception is thrown out of an async Task or async Task method, that exception is captured and placed on the Task object. With async void methods, there is no Task object, so any exceptions thrown out of an async void method will be raised directly on the SynchronizationContext that was active when the async void method started.
Best practice for async methods
I was using this code to redirect my console output to file and then read and display it. I want to go away from using files because I'm polluting my folders with those console files. How can I do this in memory ? I don't want any files to pollute the system. Maybe I'm trying something weird here. I just want 1 thread to read the console output of the very same application:
1 application
multiple threads write to console
1 thread reads from console
My working file code:
private StreamWriter currentOut = null;
private void RedirectConsole()
{
currentOut = new StreamWriter(new FileStream(filename,
FileMode.Create, FileAccess.Write, FileShare.Read));
currentOut.AutoFlush = true;
Console.SetOut(currentOut);
ThreadPool.QueueUserWorkItem(o => { Listen(); });
}
private void Listen()
{
StreamReader fileIn = new StreamReader(new FileStream(filename,
FileMode.Open, FileAccess.Read, FileShare.ReadWrite));
while (true)
{
try
{
if (!fileIn.EndOfStream)
{
string a = fileIn.ReadLine();
MessageBox.Show(a);
}
Thread.Sleep(25);
}
catch { }
}
}
This seems to be what I want. But I'm unable to implement that (help?). File is like a buffer. You write to it from one end and read from another. I need the same in memory.
Try:
private StreamWriter currentOut = null;
private MemoryStream ms = new MemoryStream();
private void RedirectConsole()
{
currentOut = new StreamWriter(ms);
currentOut.AutoFlush = true;
Console.SetOut(currentOut);
ThreadPool.QueueUserWorkItem(o => { Listen(); });
}
private void Listen()
{
StreamReader fileIn = new StreamReader(ms);
// ...
}
The problem with using MemoryStream is that the read position advances with the write position. Pipes (System.IO.Pipes namespace) are a better choice for use as temporary buffers where the read position needs to advance independent of the write position. Admittedly, this more or less does exactly what your working solution does, though it removes the need to implement the buffer yourself.
class ConsoleRedirector : IDisposable
{
private TextWriter originalOut = Console.Out;
private AnonymousPipeServerStream consoleOutServerPipe;
private StreamWriter currentOut;
public ConsoleRedirector()
{
this.consoleOutServerPipe = new AnonymousPipeServerStream(PipeDirection.Out);
this.currentOut = new StreamWriter(this.consoleOutServerPipe);
this.currentOut.AutoFlush = true;
Console.SetOut(this.currentOut);
ThreadPool.QueueUserWorkItem(o => { this.Listen(); });
}
private void Listen()
{
AnonymousPipeClientStream consoleOutClientPipe = new AnonymousPipeClientStream(PipeDirection.In, this.consoleOutServerPipe.ClientSafePipeHandle);
using (StreamReader fileIn = new StreamReader(consoleOutClientPipe))
{
// ...
}
}
public void Dispose()
{
this.currentOut.Dispose();
Console.SetOut(this.originalOut);
}
}
I ended up writing a derived stream class and replaced the FileStream with my own stream. I probably should have avoided that. But since I couldn't find a working solution, it was also a good practice. Something like this:
public class MyStream: Stream
{
private byte[] internalBuffer = new byte[4096];
// ...
public override int Read(byte[] buffer, int offset, int count)
{
// used by StreamReader
}
public override void Write(byte[] buffer, int offset, int count)
{
// used by StreamWriter
}
}
override all the other stuff, handle multi-threading while enlarging internalBuffer and disposing passed data.
I have a problem on a few systems that when we are trying to load the RichTextBox the program becomes unresponsive, we cannot do anything and will have to kill it via Taskmanager.
its working on most systems but a few systems located in a different country there seems to be problem.
we have tried something as simple as :
private void testing4()
{
richTextBox1.LoadFile(#"C:\testing.logs", RichTextBoxStreamType.PlainText);
}
If we decide to use a normal TextBox it appears to be working using .net 4.5, but it still becomes unresponsive. Any ideas?
This may help you:
foreach(var line in File.ReadLines(#"C:\testing.logs"))
{
richTextBox1.AppendText(line+Environment.NewLine);
}
Since you are using framework 4.5, you can do it async, as in MSDN example:
public async void ReadFile()
{
string filePath = #"C:\testing.logs";
if (File.Exists(filePath) == false)
{
Debug.WriteLine("file not found: " + filePath);
}
else
{
try
{
string text = await ReadTextAsync(filePath);
richTextBox1.AppendText(text);
}
catch (Exception ex)
{
Debug.WriteLine(ex.Message);
}
}
}
private async Task<string> ReadTextAsync(string filePath)
{
using (FileStream sourceStream = new FileStream(filePath,
FileMode.Open, FileAccess.Read, FileShare.Read,
bufferSize: 4096, useAsync: true))
{
StringBuilder sb = new StringBuilder();
byte[] buffer = new byte[0x1000];
int numRead;
while ((numRead = await sourceStream.ReadAsync(buffer, 0, buffer.Length)) != 0)
{
string text = Encoding.Unicode.GetString(buffer, 0, numRead);
sb.Append(text);
}
return sb.ToString();
}
}
Source: Using Async for File Access