dotnet/wpf · error · InvalidOperationException

SR.Format(SR.CreateParaBreakingSessionFailure, lserr)

Error message

SR.Format(SR.CreateParaBreakingSessionFailure, lserr)

What it means

During creation of the paragraph-breaking session in the TextParagraphCache constructor, an LS error (lserr != LsErr.None) surfaced. If an exception was thrown inside the native callbacks, it is wrapped in an InvalidOperationException with that inner exception; otherwise ThrowExceptionFromLsError throws carrying the formatted CreateParaBreakingSessionFailure message. This means the line-services paragraph-breaking session could not be established.

Solutions

Inspect the InnerException (InvalidOperationException case) for the exception thrown in your callbacks
Fix bugs in custom ITextParagraph/TextSource callback implementations
Verify paragraph properties (tabs, indents) are valid and consistent
If purely an lserr with no inner exception, treat as internal line-engine failure and isolate the text that triggers it

Example fix

// check inner exception
try { /* format paragraph */ }
catch (InvalidOperationException ex) when (ex.InnerException != null) {
    log(ex.InnerException); // exception thrown in your callbacks
}

Defensive patterns

Strategy: try-catch

Try / catch

try { /* paragraph formatting */ } catch (InvalidOperationException ex) when (ex.Message.Contains("CreateParaBreakingSessionFailure")) { var root = ex.InnerException ?? ex; log(root); }

Prevention

Fix exceptions thrown inside custom paragraph callbacks (they surface wrapped here)
Validate tab/paragraph property values before formatting
Isolate offending text/properties when reproducing

When it happens

Trigger: Constructing TextFormatterImp's paragraph cache when the native LS engine fails during CreateParaBreakingSession, either due to callback exception or an LS error code return.

Common situations: Complex paragraph layouts with custom tab/paragraph properties the LS engine rejects, or exceptions thrown inside ITextParagraph callback implementations.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of dotnet/wpf@81131a70a4 (2026-09-14). Data as JSON: /api/errors/6df624df1bfa0536. Report an issue: GitHub.

Appendix: source

Thrown at src/Microsoft.DotNet.Wpf/src/PresentationCore/System/Windows/Media/textformatting/TextParagraphCache.cs:76

                // since we handle Bidi break ourselves.
                IntPtr.Zero,
                ref ploparabreakValue,
                ref _penalizedAsJustified
                );

            // get the exception in context before it is released
            Exception callbackException = context.CallbackException;
            
            // release the context
            context.Release();

            if(lserr != LsErr.None)
            {
                GC.SuppressFinalize(this);
                if(callbackException != null)
                {                        
                    // rethrow exception thrown in callbacks
                    throw new InvalidOperationException(SR.Format(SR.CreateParaBreakingSessionFailure, lserr), callbackException);
                }
                else
                {
                    // throw with LS error codes
                    TextFormatterContext.ThrowExceptionFromLsError(SR.Format(SR.CreateParaBreakingSessionFailure, lserr), lserr);
                }
            }

            _ploparabreak = ploparabreakValue;

            // keep context alive till here
            GC.KeepAlive(context);
        }


        /// <summary>
        /// Finalizing paragraph content cache
        /// </summary>

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