Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
RegexMatchTimeoutException Class

RegexMatchTimeoutException Class

.NET Framework 4.6 and 4.5

The exception that is thrown when the execution time of a regular expression pattern-matching method exceeds its time-out interval.


Namespace:  System.Text.RegularExpressions
Assemblies:   System (in System.dll)
  System.Text.RegularExpressions (in System.Text.RegularExpressions.dll)

<SerializableAttribute> _
Public Class RegexMatchTimeoutException _
	Inherits TimeoutException _
	Implements ISerializable

The RegexMatchTimeoutException type exposes the following members.

Public methodRegexMatchTimeoutExceptionInitializes a new instance of the RegexMatchTimeoutException class with a system-supplied message.
Public methodRegexMatchTimeoutException(String)Initializes a new instance of the RegexMatchTimeoutException class with the specified message string.
Protected methodRegexMatchTimeoutException(SerializationInfo, StreamingContext)Initializes a new instance of the RegexMatchTimeoutException class with serialized data.
Public methodRegexMatchTimeoutException(String, Exception)Initializes a new instance of the RegexMatchTimeoutException class with a specified error message and a reference to the inner exception that is the cause of this exception.
Public methodRegexMatchTimeoutException(String, String, TimeSpan)Initializes a new instance of the RegexMatchTimeoutException class with information about the regular expression pattern, the input text, and the time-out interval.

Public propertyDataGets a collection of key/value pairs that provide additional user-defined information about the exception. (Inherited from Exception.)
Public propertyHelpLinkGets or sets a link to the help file associated with this exception. (Inherited from Exception.)
Public propertyHResultGets or sets HRESULT, a coded numerical value that is assigned to a specific exception. (Inherited from Exception.)
Public propertyInnerExceptionGets the Exception instance that caused the current exception. (Inherited from Exception.)
Public propertyInputGets the input text that the regular expression engine was processing when the time-out occurred.
Public propertyMatchTimeoutGets the time-out interval for a regular expression match.
Public propertyMessageGets a message that describes the current exception. (Inherited from Exception.)
Public propertyPatternGets the regular expression pattern that was used in the matching operation when the time-out occurred.
Public propertySourceGets or sets the name of the application or the object that causes the error. (Inherited from Exception.)
Public propertyStackTraceGets a string representation of the immediate frames on the call stack. (Inherited from Exception.)
Public propertyTargetSiteGets the method that throws the current exception. (Inherited from Exception.)

Public methodEquals(Object)Determines whether the specified object is equal to the current object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetBaseExceptionWhen overridden in a derived class, returns the Exception that is the root cause of one or more subsequent exceptions. (Inherited from Exception.)
Public methodGetHashCodeServes as the default hash function. (Inherited from Object.)
Public methodGetObjectDataWhen overridden in a derived class, sets the SerializationInfo with information about the exception. (Inherited from Exception.)
Public methodGetTypeGets the runtime type of the current instance. (Inherited from Exception.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringCreates and returns a string representation of the current exception. (Inherited from Exception.)

Protected eventSerializeObjectStateOccurs when an exception is serialized to create an exception state object that contains serialized data about the exception. (Inherited from Exception.)

Explicit interface implemetationPrivate methodISerializable.GetObjectDataPopulates a SerializationInfo object with the data needed to serialize a RegexMatchTimeoutException object.

The presence of a RegexMatchTimeoutException exception generally indicates one of the following conditions:

  • The regular expression engine is backtracking excessively as it attempts to match the input text to the regular expression pattern.

  • The time-out interval has been set too low, especially given high machine load.

The way in which an exception handler handles an exception depends on the cause of the exception:

  • If the time-out results from excessive backtracking, your exception handler should abandon the attempt to match the input and inform the user that a time-out has occurred in the regular expression pattern-matching method. If possible, information about the regular expression pattern, which is available from the Pattern property, and the input that caused excessive backtracking, which is available from the Input property, should be logged so that the issue can be investigated and the regular expression pattern modified. Time-outs due to excessive backtracking are always reproducible.

  • If the time-out results from setting the time-out threshold too low, you can increase the time-out interval and retry the matching operation. The current time-out interval is available from the MatchTimeout property. When a RegexMatchTimeoutException exception is thrown, the regular expression engine maintains its state so that any future invocations return the same result, as if the exception did not occur. The recommended pattern is to wait for a brief, random time interval after the exception is thrown before calling the matching method again. This can be repeated several times. However, the number of repetitions should be small in case the time-out is caused by excessive backtracking.

The example in the next section illustrates both techniques for handling a RegexMatchTimeoutException.

The following example illustrates two possible approaches to handling the RegexMatchTimeoutException exception. A constant whose value is two seconds defines the maximum time-out interval. The Regex.IsMatch(String, String, RegexOptions, TimeSpan) method is initially called with a time-out interval of one second. Each RegexMatchTimeoutException exception causes the time-out interval to be increased by one second and results in another call to the Regex.IsMatch method if the current time-out interval is less than the maximum time-out interval. However, if the current time-out interval exceeds the maximum time-out interval, the exception handler writes information to the event log and abandons the processing of the regular expression.

Imports System.ComponentModel
Imports System.Diagnostics
Imports System.Security
Imports System.Text.RegularExpressions
Imports System.Threading

Module Example
   Const MaxTimeoutInSeconds As Integer = 2

   Public Sub Main()
      Dim timeout As TimeSpan = New TimeSpan(0, 0, 1)

      Dim input As String = "aaaaaaaaaaaaaaaaaaaaaa>" 
      If ValidateInput(input, timeout) Then 
         ' Perform some operation with valid input string.
         Console.WriteLine("'{0}' is a valid string.", input) 
      End If 
   End Sub  

   Private Function ValidateInput(input As String, 
                                  timeout As TimeSpan) As Boolean 
      Dim pattern As String = "(a+)+$"       
         Return Regex.IsMatch(input, pattern, 
                              RegexOptions.IgnoreCase, timeout)
      Catch e As RegexMatchTimeoutException
         ' Increase the timeout interval and retry.
         timeout = timeout.Add(New TimeSpan(0, 0, 1))
         Console.WriteLine("Changing the timeout interval to {0}", 
         If timeout.TotalSeconds <= MaxTimeoutInSeconds Then 
            ' Pause for a short interval.
            Return ValidateInput(input, timeout)
            Console.WriteLine("Timeout interval of {0} exceeded.", 
            ' Write to event log named RegexTimeouts 
               If Not EventLog.SourceExists("RegexTimeouts") Then
                  EventLog.CreateEventSource("RegexTimeouts", "RegexTimeouts")
               End If    
               Dim log As New EventLog("RegexTimeouts")
               log.Source = "RegexTimeouts" 
               Dim msg As String = String.Format("Timeout after {0} matching '{1}' with '{2}.",
                                                 e.MatchTimeout, e.Input, e.Pattern)
               log.WriteEntry(msg, EventLogEntryType.Error)
            ' Do nothing to handle the exceptions. 
            Catch ex As SecurityException

            Catch ex As InvalidOperationException

            Catch ex As Win32Exception

            End Try    
            Return False 
         End If    
      End Try 
   End Function 
End Module 
' The example writes to the event log and also displays the following output: 
'       Changing the timeout interval to 00:00:02 
'       Changing the timeout interval to 00:00:03 
'       Timeout interval of 00:00:03 exceeded.

.NET Framework

Supported in: 4.6, 4.5

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
© 2015 Microsoft