[Mono-dev] Patch: System.ServiceModel.Logger not thread-safe

[Uli Hertlein]

Hi guys,

I believe I've discovered a bug in System.ServiceModel.Logger that can 
cause unhandled exceptions when it's used from different threads.

My code occasionally would get tripped up with something like this:

Exception This XmlWriter does not accept Attribute at this state Content.
   at System.Xml.XmlTextWriter.WriteStartAttribute (System.String 
prefix, System.String localName, System.String namespaceUri) [0x002a8] 
in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/XmlTextWriter2.cs:905 

   at System.Xml.DefaultXmlWriter.WriteStartAttribute (System.String 
prefix, System.String localName, System.String ns) [0x00000] in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/DefaultXmlWriter.cs:196 

   at System.Xml.XmlWriter.WriteAttributeString (System.String prefix, 
System.String localName, System.String ns, System.String value) 
[0x00000] in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/XmlWriter.cs:264
   at System.Xml.XmlWriter.WriteAttributeString (System.String 
localName, System.String value) [0x00000] in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/XmlWriter.cs:251
   at System.ServiceModel.Logger.TraceCore (TraceEventType eventType, 
Int32 id, Boolean hasRelatedActivity, Guid relatedActivity, 
System.Object[] data) [0x000fb] in 
/Users/uli/src/Mono/mono/mcs/class/System.ServiceModel/System.ServiceModel/Logger.cs:248 

   at System.ServiceModel.Logger.LogMessage 
(System.ServiceModel.Diagnostics.MessageLogTraceRecord log) [0x000ac] in 
/Users/uli/src/Mono/mono/mcs/class/System.ServiceModel/System.ServiceModel/Logger.cs:202 

   at System.ServiceModel.Logger.LogMessage (MessageLogSourceKind 
sourceKind, System.ServiceModel.Channels.Message& msg, Int64 
maxMessageSize) [0x00029] in 
/Users/uli/src/Mono/mono/mcs/class/System.ServiceModel/System.ServiceModel/Logger.cs:170 


Unhandled Exception: System.InvalidOperationException: This XmlWriter 
does not accept StartTag at this state Error.
   at System.Xml.XmlTextWriter.WriteStartElement (System.String prefix, 
System.String localName, System.String namespaceUri) [0x0032e] in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/XmlTextWriter2.cs:692 

   at System.Xml.DefaultXmlWriter.WriteStartElement (System.String 
prefix, System.String localName, System.String ns) [0x00000] in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/DefaultXmlWriter.cs:214 

   at System.Xml.XmlWriter.WriteStartElement (System.String localName, 
System.String ns) [0x00000] in 
/Users/uli/src/Mono/mono/mcs/class/System.XML/System.Xml/XmlWriter.cs:610
   at System.ServiceModel.Logger.TraceCore (TraceEventType eventType, 
Int32 id, Boolean hasRelatedActivity, Guid relatedActivity, 
System.Object[] data) [0x0002e] in 
/Users/uli/src/Mono/mono/mcs/class/System.ServiceModel/System.ServiceModel/Logger.cs:226 

   at System.ServiceModel.Logger.Log (TraceEventType eventType, 
System.String message, System.Object[] args) [0x0000c] in 
/Users/uli/src/Mono/mono/mcs/class/System.ServiceModel/System.ServiceModel/Logger.cs:147

Today's debug session showed that it would happen when Logger.LogMessage 
is called from different threads (concurrent access to log_writer and 
xml_writer), which would eventually happen after some time.

My fix was to lock 'log_writer' before use. A patch against git 
mono-2.10 is attached.

Cheers,
/uli
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