I am currently working on a C# project that uses a FileStream to open a file and passes the information to a StreamReader for it to be processed.
What I want to be able to do is I have a method which passes the stream to another method, that does the processing and once that method finishes, the original method calls another method passing it the same stream. However, when the first stream process completes when the second method is called it displays an exception saying that the thread is not readable.
When I look at debugging the stream, when I look at the details about the stream it says that it cannot be read, seek or write, and the length parameter of the stream says threw an exception of type System.ObjectDisposedException.
The question is, how can I keep the stream readable after the first method has completed so that the same stream can be processed in the second stream.
Thanks for any help you can provide.
if your streamReader is part of "using" statement, it disposes the file stream in the end of the statement block.
using (StreamReader reader = new StreamReader(fileStream))
{
..
}
Simple solution is not to dispose the reader explicitly, leaving it to GC
[More thoughts]
If most of the methods are accessing file stream through TextReader interface, you can pass reader thus avoiding the problem with the ownership.
If I understood you correctly, your stream is getting closed too fast. Based on what you say, it might be because you are Closing or Disposing StreamReader which, according to documentation, will close underlying stream.
Try not closing StreamReader (just ignore it, after it's not needed).
For example, if your code looks like this:
void P()
{
var stream = new FileStream();
P1(stream);
P2(stream);
}
void P1(FileStream stream)
{
using (var reader = new StreamReader(stream))
{
......
} //Here you would have disposed StreamReader and close FileStream
}
void P2(FileStream stream) // Stream is already closed
{
}
You have closed your stream in 1st method. You will have the same problem if you call:
reader.Dispose();
reader.Close();
stream.Dispose();
stream.Close();
using (stream);
So make sure aren't doing any of those things.
Btw: in C#5 I have heard, that Readers/Writers will be parametrized, if you want then to close underlying stream when they are closed (just like CryptoStream have right now)
Related
I was searching in StackOverflow about try-finally and using blocks and what are the best practices on using them.
I read in a comment here that if your application is terminated abruptly by killing the process, a finally block will not get executed.
I was wondering, does the same apply to the using blocks? Will for example a stream get closed if a Environment.exit() call occurs inside the using block?:
//....
using (FileStream fsSource1 = new FileStream(pathSource,
FileMode.Open, FileAccess.Read))
{
//Use the stream here
Environment.exit();
}
As a second thought on it, and knowing that CLR Garbage Collector will probably take care of the stream objects if not closed properly in the program calls, is it considered necessary to close a stream in code, if the program gets terminated for sure after the completion of the stream usage?
For example, is there any practical difference between:
//....
using (FileStream fsSource1 = new FileStream(pathSource,
FileMode.Open, FileAccess.Read))
{
//Use the stream here
}
Environment.exit();
And:
//....
FileStream fsSource1 = new FileStream(pathSource, FileMode.Open, FileAccess.Read);
//Use the stream here
Environment.exit();
Or even the example mentioned before?
It shouldn't make a difference in the specific case of FileStream, modulo a tricky corner case when you used its BeginWrite() method. Its finalizer attempts to complete writing any unwritten data still present in its internal buffer. This is however not generally true, it will make a difference if you use StreamWriter for example.
What you are leaving up to the .NET Framework to decide is whether you truly meant to jerk the floor mat and seize writing the file. Or whether it should make a last-gasp attempt to flush any unwritten data. The outcome in the case of StreamWriter will tend to be an unpleasant one, non-zero odds that something is going to fall over when it tries to read a half-written file.
Always be explicit, if you want to make sure this does not happen then it is up to you to ensure that you properly called the Close() or Dispose() method. Or delete the file.
I serve various TCP clients asynchronously via their respective TCP sockets. Currently, I have 3 tasks running simultaneously:
Await data from the NetworkStream using await StreamReader.ReadAsync()
Write data into the NetworkStream using await StreamWriter.WriteAsync()
Send watchdog messages periodically
Now, when I call something like this:
var stream = new NetworkStream(_socket);
// reading task
using (var reader = new StreamReader(stream)) {
// ...read...
}
The underlying NetworkStream gets eventually destroyed after reading has been done because StreamReader closes it on Dispose().
The easiest way would be not closing the StreamReader, but AFAIK this is a very bad idea. So, how can I handle asynchronous reading and writing while keeping the socket connection open?
From .NET 4.5 onwards, if you look through the constructor overloads for StreamReader and StreamWriter, there is one (and currently only one) constructor that takes a bool leaveOpen parameter. Use this overload and pass true - then it won't feel ownership of the underlying stream.
If this isn't available on your framework version, you'll have to create a NonClosingStream : Stream that decorates a stream using pass-thru implementations for everything except Close() and Dispose(), which should be no-ops (well, they could assign null to the field that represents the wrapped stream, but nothing more).
Since the StreamReader will always dispose the underling stream on its own disposal (that's why actually it is IDisposable), you do indeed have to not close it until you have no need in the network stream anymore.
So, this is very ok for the situation:
var stream = new NetworkStream(_socket);
var reader = new StreamReader(stream);
And when you are finish, you would close both of them, right?
reader.Dispose();
stream.Dispose();
I have a class that essentially wraps a Stream for reading/writing, but that stream is expected to be managed by the consumer of that class. For ease of use, I use StreamReader and StreamWriter classes to perform I/O operations on the stream. Normally I'd wrap the reader and writer in using blocks, but I want to avoid closing the reader and writer because doing so also closes the underlying stream and I have to keep it open.
Is it safe in terms of memory/resource management to not close a StreamReader/StreamWriter if I expect the underlying Stream to be managed by the caller? Will the reader and writer be garbage collected when the stream is explicitly closed elsewhere?
public class Wrapper
{
private Stream _underlyingStream;
public Wrapper(Stream underlyingStream)
{
_underlyingStream = underlyingStream;
}
public string GetValue()
{
_underlyingStream.Seek(0, SeekOrigin.Begin);
var reader = new StreamReader(_underlyingStream);
return reader.ReadToEnd(); // we're done, but the stream is not ours to close
}
}
If nobody closes the streams then ultimately the finalizer will be called which should call dispose and close them upon GC. But that's quite a crap-shoot resource-wise because it leaves whatever possibly-expensive resources allocated until GC. It could get worse the longer your object lives, especially if it survives collections to be promoted to gen 1 or even 2.
It sure would be nice if you could present something to your caller that isolates this. Perhaps you can cache something from the stream so you can close it while still serving the content to your caller?
EDIT after your edit: Now that I see your caller PASSES you a stream to operate on, my answer has to be different! It's very clear that your caller should be managing the stream's lifetime. I had the impression at first that your class created a stream and hoped the caller managed it.
The easiest way to solve this is to wrap the stream in your own class that derives from System.IO.Stream
Example:
http://csharptest.net/browse/src/Library/IO/NonClosingStream.cs
It is definetelly not ok.
read this from msdn
The close calls the Dispose method passing a true value.
Flushing the stream will not flush its underlying encoder unless you explicitly call Close.
Try to encapsulate all IO in a class.
Using method: System.IO.File.Create()
After the file gets created, it still remains used by a process, and I can't delete it.
Any idea how I can better create the file, should be a 0byte file, and then somehow close and dispose?
JL,
You should wrap your call to .Create in a using statement so that the FileStream that .Create returns will be closed properly. IE:
using (File.Create("path")){...}
The Create method not only creates the file, it opens it and return a FileStream object that you can use to write to the file.
You have to close the file after yourself, otherwise it will not be closed before the garbage collector cleans up the FileStream object.
The easiest way is to simply close the file using the reference that the Create method returns:
File.Create(fileName).Close();
nikmd23 has the short answer, the long answer is: the FileStream that File.Create(...) is returning is not being deterministically disposed of, therefore it's file handle is not closed when you're trying to delete it.
As nikmd23 put it, wrapping your File.Create(...) call will with a using statement will make sure the stream is closed and disposed of:
using (FileStream fs = File.Create(path)) {
// do anything with the stream if need-be...
}
File.Delete(path); //after it's been disposed of.
The using(...) block is really just compiler-sugar for:
FileStream fs = File.Create(path);
try {
// do anything with the stream if need-be...
}
finally {
fs.Dispose();
}
File.Delete(path)
You should use nikmd23's answer in almost all cases. If you can't, because you need to pass the FileStream somewhere else, make sure to call the FileStream.Close method eventually. Preferably you would have the class that 'owns' the FileStream implement IDisposable itself, and close the stream in its Dispose method.
For more information on implementing IDisposable, refer to the MSDN documentation. Easier reading, and more up to date, is Joe Duffy's post on the subject.
using(FileStream f = File.Create(file_path))
{
// ... do something with file
f.Close();
}
The "f.Close();" line closing file immediately. If not close manually, Disposing may not close it.
See System.IO.File.Create(String) Method paramter and return value description
Parameters
path
Type: System.String
The path and name of the file to create.
Return Value
Type: System.IO.FileStream
A FileStream that provides read/write access to the file specified in path.
The FileStream return value is there for IO access to the created file. If you are not interested in writing (or reading) the newly created file, close the stream. That is what the using block is ensuring.
Given a method
public static string[] Foo(System.IO.Stream stream)
{
XmlTextWriter xmlWriter = new XmlTextWriter(stream, System.Text.Encoding.ASCII);
xmlWriter.WriteStartDocument();
xmlWriter.WriteStartElement("Element");
xmlWriter.WriteEndElement();
xmlWriter.WriteEndDocument();
xmlWriter.Flush();
return new string[3]{"1", "2", "3"};
}
and a calling code
using(MemoryStream memStream = new MemoryStream())
{
string[] playerIDs = PlayerCommand.Foo(stream);
// do some stuff with stream and playerIDs
}
When the control passes out of the using directive, is there a problem that xmlWriter was not explicitly closed in Foo (which would make the stream useless)?
Also, is passing a Stream between methods unsavory, is there a better way to pass the results of XMLWriting back to the calling code (which will zip it up and file it away)?
Thanks in advance,
Greg
No problem here. A StreamWriter's Dispose() method basically first calls Flush() and then disposes the underlying stream, so as long as you have the Flush() covered yourself (which you do above) it's OK to leave it hanging as long as the stream's alive.
The other answers suggest disposing the Writer itself, but that's not really an option here, because it will dispose the underlying stream as well.
That said, if you're just putting an XML document in the stream and then using it later, I'd rather pass the XML document itself around instead of keeping track of the stream. But perhaps your code isn't as simple as all that.