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Fix parallel use of not thread-safe SubtitleFormat instance

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`SubtitleFormat`'s `LoadSubtitle()` function is
not thread-safe.

A `SubtitleEditParser` instance's `Parse()`
function can be called from multiple threads at
the same time.

`SubtitleFormat`s are cached in the constructor
of each `SubtitleEditParser`, and the same
instances are used for each possibly parallel
`Parse()` function call, which causes subtitle
parse problems.

This patch modifies the code, so we only cache
the extension -> `SubtitleFormat` type/class
mapping and create a new `SubtitleFormat`
instance in each `Parse()` call, so no
`SubtitleFormat` instance is accessed from
multiple threads.

Fixes #12113

Kudos for everyone investigating the issue there,
most notably @RenV123 for PoC-ing the solution.

Signed-off-by: Attila Szakacs <szakacs.attila96@gmail.com>
This commit is contained in:
Attila Szakacs 2025-01-17 10:40:32 +01:00
parent 344cc8b97b
commit c693da94ce
1 changed files with 23 additions and 14 deletions
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37
MediaBrowser.MediaEncoding/Subtitles/SubtitleEditParser.cs
View File

@ -17,7 +17,7 @@ namespace MediaBrowser.MediaEncoding.Subtitles
public class SubtitleEditParser : ISubtitleParser public class SubtitleEditParser : ISubtitleParser
{ {
private readonly ILogger<SubtitleEditParser> _logger; private readonly ILogger<SubtitleEditParser> _logger;
private readonly Dictionary<string, SubtitleFormat[]> _subtitleFormats; private readonly Dictionary<string, List<Type>> _subtitleFormatTypes;
/// <summary> /// <summary>
/// Initializes a new instance of the <see cref="SubtitleEditParser"/> class. /// Initializes a new instance of the <see cref="SubtitleEditParser"/> class.
@ -26,10 +26,7 @@ namespace MediaBrowser.MediaEncoding.Subtitles
public SubtitleEditParser(ILogger<SubtitleEditParser> logger) public SubtitleEditParser(ILogger<SubtitleEditParser> logger)
{ {
_logger = logger; _logger = logger;
_subtitleFormats = GetSubtitleFormats() _subtitleFormatTypes = GetSubtitleFormatTypes();
.Where(subtitleFormat => !string.IsNullOrEmpty(subtitleFormat.Extension))
.GroupBy(subtitleFormat => subtitleFormat.Extension.TrimStart('.'), StringComparer.OrdinalIgnoreCase)
.ToDictionary(g => g.Key, g => g.ToArray(), StringComparer.OrdinalIgnoreCase);
} }
/// <inheritdoc /> /// <inheritdoc />
@ -38,13 +35,14 @@ namespace MediaBrowser.MediaEncoding.Subtitles
var subtitle = new Subtitle(); var subtitle = new Subtitle();
var lines = stream.ReadAllLines().ToList(); var lines = stream.ReadAllLines().ToList();
if (!_subtitleFormats.TryGetValue(fileExtension, out var subtitleFormats)) if (!_subtitleFormatTypes.TryGetValue(fileExtension, out var subtitleFormatTypesForExtension))
{ {
throw new ArgumentException($"Unsupported file extension: {fileExtension}", nameof(fileExtension)); throw new ArgumentException($"Unsupported file extension: {fileExtension}", nameof(fileExtension));
} }
foreach (var subtitleFormat in subtitleFormats) foreach (var subtitleFormatType in subtitleFormatTypesForExtension)
{ {
var subtitleFormat = (SubtitleFormat)Activator.CreateInstance(subtitleFormatType, true)!;
_logger.LogDebug( _logger.LogDebug(
"Trying to parse '{FileExtension}' subtitle using the {SubtitleFormatParser} format parser", "Trying to parse '{FileExtension}' subtitle using the {SubtitleFormatParser} format parser",
fileExtension, fileExtension,
@ -97,11 +95,11 @@ namespace MediaBrowser.MediaEncoding.Subtitles
/// <inheritdoc /> /// <inheritdoc />
public bool SupportsFileExtension(string fileExtension) public bool SupportsFileExtension(string fileExtension)
=> _subtitleFormats.ContainsKey(fileExtension); => _subtitleFormatTypes.ContainsKey(fileExtension);
private List<SubtitleFormat> GetSubtitleFormats() private Dictionary<string, List<Type>> GetSubtitleFormatTypes()
{ {
var subtitleFormats = new List<SubtitleFormat>(); var subtitleFormatTypes = new Dictionary<string, List<Type>>(StringComparer.OrdinalIgnoreCase);
var assembly = typeof(SubtitleFormat).Assembly; var assembly = typeof(SubtitleFormat).Assembly;
foreach (var type in assembly.GetTypes()) foreach (var type in assembly.GetTypes())
@ -113,9 +111,20 @@ namespace MediaBrowser.MediaEncoding.Subtitles
try try
{ {
// It shouldn't be null, but the exception is caught if it is var tempInstance = (SubtitleFormat)Activator.CreateInstance(type, true)!;
var subtitleFormat = (SubtitleFormat)Activator.CreateInstance(type, true)!; var extension = tempInstance.Extension.TrimStart('.');
subtitleFormats.Add(subtitleFormat); if (!string.IsNullOrEmpty(extension))
{
// Store only the type, we will instantiate from it later
if (!subtitleFormatTypes.TryGetValue(extension, out var subtitleFormatTypesForExtension))
{
subtitleFormatTypes[extension] = [type];
}
else
{
subtitleFormatTypesForExtension.Add(type);
}
}
} }
catch (Exception ex) catch (Exception ex)
{ {
@ -123,7 +132,7 @@ namespace MediaBrowser.MediaEncoding.Subtitles
} }
} }
return subtitleFormats; return subtitleFormatTypes;
} }
} }
} }