/// <summary>
/// Partially fill out BreakRecordTable by pre-calculating BreakRecords.
/// This callback is invoked when background pagination is enabled and
/// BreakRecordTable is not completely updated yet.
/// </summary>
private object OnBackgroundPagination(object arg)
{
DateTime dtStart = DateTime.Now;
DateTime dtStop;
_backgroundPaginationOperation = null; // Clear out pending request.
// Ensure usage from just one Dispatcher object.
// FlowDocumentPaginator runs its own layout, hence there is a need
// to protect it from random access from other threads.
_dispatcherObject.VerifyAccess();
// Detect reentrancy.
if (_document.StructuralCache.IsFormattingInProgress)
{
throw new InvalidOperationException(SR.Get(SRID.FlowDocumentFormattingReentrancy));
}
// Ignore this formatting request, if the element was already disposed.
if (_document.StructuralCache.PtsContext.Disposed)
{
return(null);
}
// Disable processing of the queue during blocking operations to prevent unrelated reentrancy.
using (_document.Dispatcher.DisableProcessing())
{
_document.StructuralCache.IsFormattingInProgress = true; // Set reentrancy flag
try
{
for (int index = 0; index < _asyncRequests.Count; index++)
{
AsyncRequest asyncRequest = _asyncRequests[index];
if (asyncRequest.Process())
{
_asyncRequests.RemoveAt(index);
index--; // Offset the index add
}
}
dtStop = DateTime.Now;
if (_backgroundPagination && !_brt.IsClean)
{
// Calculate BreakRecords until entire content is calculated or
// specific time span has been exceeded (_paginationTimeout).
while (!_brt.IsClean)
{
// Get the first invalid entry in the BreakRecordTable, calculate
// BreakRecord for it and update BreakRecordTable with the calculated
// value.
FormatPage(_brt.Count);
// Update time span.
dtStop = DateTime.Now;
long timeSpan = (dtStop.Ticks - dtStart.Ticks) / TimeSpan.TicksPerMillisecond;
if (timeSpan > _paginationTimeout)
{
break;
}
}
// Initiate the next async operation.
InitiateNextAsyncOperation();
}
}
finally
{
_document.StructuralCache.IsFormattingInProgress = false; // Clear reentrancy flag.
}
}
return(null);
}