public FontFileStream(IFontSource fontSource)
{
// Previously we were using fontSource->GetStream() which caused crashes in the XPS scenarios
// as the stream was getting closed by some other object. In XPS scenarios GetStream() would return
// MS::Internal::IO:Packaging::SynchronizingStream which is owned by the XPS docs and
// is known to have issues regarding the lifetime management where by if the current XPS page is
// flipped then the stream will get disposed. Thus, we cannot rely on the stream directly and hence we now use
// fontSource->GetUnmanagedStream() which returns a copy of the content of the stream. Special casing XPS will not
// guarantee that this problem will be fixed so we will use the GetUnmanagedStream(). Note: This path will only
// be taken for embedded fonts among which XPS is a main scenario. For local fonts we use DWrite's APIs.
_fontSourceStream = fontSource.GetUnmanagedStream();
try
{
_lastWriteTime = fontSource.GetLastWriteTimeUtc().ToFileTimeUtc();
}
catch (ArgumentOutOfRangeException) //The resulting file time would represent a date and time before 12:00 midnight January 1, 1601 C.E. UTC.
{
_lastWriteTime = -1;
}
// Create lock to control access to font source stream.
_fontSourceStreamLock = new Object();
}