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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System;
using System.Collections.Immutable;
using System.Diagnostics;
using System.IO;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Host;
using Microsoft.CodeAnalysis.Internal.Log;
using Microsoft.CodeAnalysis.Text;
using Roslyn.Utilities;
namespace Microsoft.CodeAnalysis
{
[DebuggerDisplay("{GetDebuggerDisplay(), nq}")]
public class FileTextLoader : TextLoader
{
private static readonly ConditionalWeakTable<Type, StrongBox<bool>> s_isObsoleteCreateTextOverriden = new();
/// <summary>
/// Absolute path of the file.
/// </summary>
public string Path { get; }
/// <summary>
/// Specifies an encoding to be used if the actual encoding of the file
/// can't be determined from the stream content (the stream doesn't start with Byte Order Mark).
/// If <c>null</c> auto-detect heuristics are used to determine the encoding.
/// Note that if the stream starts with Byte Order Mark the value of <see cref="DefaultEncoding"/> is ignored.
/// </summary>
public Encoding? DefaultEncoding { get; }
/// <summary>
/// Creates a content loader for specified file.
/// </summary>
/// <param name="path">An absolute file path.</param>
/// <param name="defaultEncoding">
/// Specifies an encoding to be used if the actual encoding can't be determined from the stream content (the stream doesn't start with Byte Order Mark).
/// If not specified auto-detect heuristics are used to determine the encoding.
/// Note that if the stream starts with Byte Order Mark the value of <paramref name="defaultEncoding"/> is ignored.
/// </param>
/// <exception cref="ArgumentNullException"><paramref name="path"/> is null.</exception>
/// <exception cref="ArgumentException"><paramref name="path"/> is not an absolute path.</exception>
public FileTextLoader(string path, Encoding? defaultEncoding)
{
CompilerPathUtilities.RequireAbsolutePath(path, "path");
Path = path;
DefaultEncoding = defaultEncoding;
}
/// <summary>
/// We have this limit on file size to reduce a chance of OOM when user adds massive files to the solution (often by accident).
/// The threshold is 100MB which came from some internal data on big files and some discussion.
/// </summary>
internal virtual int MaxFileLength => 100 * 1024 * 1024;
internal sealed override string FilePath => Path;
internal override bool CanReloadText => !IsObsoleteCreateTextOverridden;
#pragma warning disable CS0618 // Type or member is obsolete
private bool IsObsoleteCreateTextOverridden
=> s_isObsoleteCreateTextOverriden.GetValue(
GetType(), _ => new StrongBox<bool>(new Func<Stream, Workspace, SourceText>(CreateText).Method.DeclaringType != typeof(FileTextLoader))).Value;
#pragma warning restore
/// <summary>
/// Creates <see cref="SourceText"/> from <see cref="Stream"/>.
/// </summary>
/// <param name="stream">Stream.</param>
/// <param name="workspace">Obsolete. Null.</param>
protected virtual SourceText CreateText(Stream stream, Workspace? workspace)
=> EncodedStringText.Create(stream, DefaultEncoding, checksumAlgorithm: SourceHashAlgorithms.Default);
/// <summary>
/// Creates <see cref="SourceText"/> from <see cref="Stream"/>.
/// </summary>
#pragma warning disable CS0618 // Type or member is obsolete
private protected virtual SourceText CreateText(Stream stream, LoadTextOptions options, CancellationToken cancellationToken)
=> IsObsoleteCreateTextOverridden
? CreateText(stream, workspace: null)
: EncodedStringText.Create(stream, DefaultEncoding, checksumAlgorithm: options.ChecksumAlgorithm);
#pragma warning restore
[Obsolete("Use/override LoadTextAndVersionAsync(LoadTextOptions, CancellationToken)", false)]
public override Task<TextAndVersion> LoadTextAndVersionAsync(Workspace? workspace, DocumentId? documentId, CancellationToken cancellationToken)
=> base.LoadTextAndVersionAsync(workspace, documentId, cancellationToken);
/// <summary>
/// Load a text and a version of the document in the workspace.
/// </summary>
/// <exception cref="IOException"></exception>
/// <exception cref="InvalidDataException"></exception>
public override async Task<TextAndVersion> LoadTextAndVersionAsync(LoadTextOptions options, CancellationToken cancellationToken)
{
ValidateFileLength(Path);
var prevLastWriteTime = FileUtilities.GetFileTimeStamp(Path);
TextAndVersion textAndVersion;
// In many .NET Framework versions (specifically the 4.5.* series, but probably much earlier
// and also later) there is this particularly interesting bit in FileStream.BeginReadAsync:
//
// // [ed: full comment clipped for brevity]
// //
// // If we did a sync read to fill the buffer, we could avoid the
// // problem, and any async read less than 64K gets turned into a
// // synchronous read by NT anyways...
// if (numBytes < _bufferSize)
// {
// if (_buffer == null) _buffer = new byte[_bufferSize];
// IAsyncResult bufferRead = BeginReadCore(_buffer, 0, _bufferSize, null, null, 0);
// _readLen = EndRead(bufferRead);
//
// In English, this means that if you do a asynchronous read for smaller than _bufferSize,
// this is implemented by the framework by starting an asynchronous read, and then
// blocking your thread until that read is completed. The comment implies this is "fine"
// because the asynchronous read will actually be synchronous and thus EndRead won't do
// any blocking -- it'll be an effective no-op. In theory, everything is fine here.
//
// In reality, this can end very poorly. That read in fact can be asynchronous, which means the
// EndRead will enter a wait and block the thread. If we are running that call to ReadAsync on a
// thread pool thread that completed a previous piece of IO, it means there has to be another
// thread available to service the completion of that request in order for our thread to make
// progress. Why is this worse than the claim about the operating system turning an
// asynchronous read into a synchronous one? If the underlying native ReadFile completes
// synchronously, that would mean just our thread is being blocked, and will be unblocked once
// the kernel gets done with our work. In this case, if the OS does do the read asynchronously
// we are now dependent on another thread being available to unblock us.
//
// So how does ths manifest itself? We have seen dumps from customers reporting hangs where
// we have over a hundred thread pool threads all blocked on EndRead() calls as we read this stream.
// In these cases, the user had just completed a build that had a bunch of XAML files, and
// this resulted in many .g.i.cs files being written and updated. As a result, Roslyn is trying to
// re-read them to provide a new compilation to the XAML language service that is asking for it.
// Inspecting these dumps and sampling some of the threads made some notable discoveries:
//
// 1. When there was a read blocked, it was the _last_ chunk that we were reading in the file in
// the file that we were reading. This leads me to believe that it isn't simply very slow IO
// (like a network drive), because in that case I'd expect to see some threads in different
// places than others.
// 2. Some stacks were starting by the continuation of a ReadAsync, and some were the first read
// of a file from the background parser. In the first case, all of those threads were if the
// files were over 4K in size. The ones with the BackgroundParser still on the stack were files
// less than 4K in size.
// 3. The "time unresponsive" in seconds correlated with roughly the number of threads we had
// blocked, which makes me think we were impacted by the once-per-second hill climbing algorithm
// used by the thread pool.
//
// So what's my analysis? When the XAML language service updated all the files, we kicked off
// background parses for all of them. If the file was over 4K the asynchronous read actually did
// happen (see point #2), but we'd eventually block the thread pool reading the last chunk.
// Point #1 confirms that it was always the last chunk. And in small file cases, we'd block on
// the first chunk. But in either case, we'd be blocking off a thread pool thread until another
// thread pool thread was available. Since we had enough requests going (over a hundred),
// sometimes the user got unlucky and all the threads got blocked. At this point, the CLR
// started slowly kicking off more threads, but each time it'd start a new thread rather than
// starting work that would be needed to unblock a thread, it just handled an IO that resulted
// in another file read hitting the end of the file and another thread would get blocked. The
// CLR then must kick off another thread, rinse, repeat. Eventually it'll make progress once
// there's no more pending IO requests, everything will complete, and life then continues.
//
// To work around this issue, we set bufferSize to 1, which means that all reads should bypass
// this logic. This is tracked by https://github.com/dotnet/corefx/issues/6007, at least in
// corefx. We also open the file for reading with FileShare mode read/write/delete so that
// we do not lock this file.
using (var stream = FileUtilities.RethrowExceptionsAsIOException(() => new FileStream(Path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete, bufferSize: 1, useAsync: true)))
{
var version = VersionStamp.Create(prevLastWriteTime);
// we do this so that we asynchronously read from file. and this should allocate less for IDE case.
// but probably not for command line case where it doesn't use more sophisticated services.
using var readStream = await SerializableBytes.CreateReadableStreamAsync(stream, cancellationToken: cancellationToken).ConfigureAwait(false);
var text = CreateText(readStream, options, cancellationToken);
textAndVersion = TextAndVersion.Create(text, version, Path);
}
// Check if the file was definitely modified and closed while we were reading. In this case, we know the read we got was
// probably invalid, so throw an IOException which indicates to our caller that we should automatically attempt a re-read.
// If the file hasn't been closed yet and there's another writer, we will rely on file change notifications to notify us
// and reload the file.
var newLastWriteTime = FileUtilities.GetFileTimeStamp(Path);
if (!newLastWriteTime.Equals(prevLastWriteTime))
{
var message = string.Format(WorkspacesResources.File_was_externally_modified_colon_0, Path);
throw new IOException(message);
}
return textAndVersion;
}
/// <summary>
/// Load a text and a version of the document.
/// </summary>
/// <exception cref="IOException"></exception>
/// <exception cref="InvalidDataException"></exception>
internal override TextAndVersion LoadTextAndVersionSynchronously(LoadTextOptions options, CancellationToken cancellationToken)
{
ValidateFileLength(Path);
var prevLastWriteTime = FileUtilities.GetFileTimeStamp(Path);
TextAndVersion textAndVersion;
// Open file for reading with FileShare mode read/write/delete so that we do not lock this file.
using (var stream = FileUtilities.RethrowExceptionsAsIOException(() => new FileStream(Path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete, bufferSize: 4096, useAsync: false)))
{
var version = VersionStamp.Create(prevLastWriteTime);
var text = CreateText(stream, options, cancellationToken);
textAndVersion = TextAndVersion.Create(text, version, Path);
}
// Check if the file was definitely modified and closed while we were reading. In this case, we know the read we got was
// probably invalid, so throw an IOException which indicates to our caller that we should automatically attempt a re-read.
// If the file hasn't been closed yet and there's another writer, we will rely on file change notifications to notify us
// and reload the file.
var newLastWriteTime = FileUtilities.GetFileTimeStamp(Path);
if (!newLastWriteTime.Equals(prevLastWriteTime))
{
var message = string.Format(WorkspacesResources.File_was_externally_modified_colon_0, Path);
throw new IOException(message);
}
return textAndVersion;
}
private string GetDebuggerDisplay()
=> nameof(Path) + " = " + Path;
private void ValidateFileLength(string path)
{
// Validate file length is under our threshold.
// Otherwise, rather than reading the content into the memory, we will throw
// InvalidDataException to caller of FileTextLoader.LoadText to deal with
// the situation.
//
// check this (http://source.roslyn.io/#Microsoft.CodeAnalysis.Workspaces/Workspace/Solution/TextDocumentState.cs,132)
// to see how workspace deal with exception from FileTextLoader. other consumer can handle the exception differently
var fileLength = FileUtilities.GetFileLength(path);
if (fileLength > MaxFileLength)
{
// log max file length which will log to VS telemetry in VS host
Logger.Log(FunctionId.FileTextLoader_FileLengthThresholdExceeded, KeyValueLogMessage.Create(m =>
{
m["FileLength"] = fileLength;
m["Ext"] = PathUtilities.GetExtension(path);
}));
var message = string.Format(WorkspacesResources.File_0_size_of_1_exceeds_maximum_allowed_size_of_2, path, fileLength, MaxFileLength);
throw new InvalidDataException(message);
}
}
}
}
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