ExpandableMemoryStream
ExpandableMemoryStream is a segmented in-memory stream designed for efficient large or parallel PDF operations. Instead of resizing a single contiguous array like a MemoryStream, it grows by adding fixed-size blocks as needed—avoiding costly reallocations and Large Object Heap (LOH) pressure. Each block remains untouched once filled, so data isn’t copied during expansion. This block-based approach keeps allocations small and predictable, reduces GC overhead, and supports very large or bursty workloads. When growing, new cleared blocks are appended. When shrinking, only the visible length changes, allowing future reuse of existing memory without additional allocations.
When to Use
Use it when you need to:
- Build or merge large PDFs fully in memory before saving.
- Combine many pieces where the final size is unknown.
- Run multiple document builds in parallel and want steady, predictable allocations.
- Seek and rewrite parts of the buffered content without triggering array growth copies.
Example
The following example shows two common ways to load a large PDF document into memory before further processing. The first approach constructs the stream directly from a byte array and passes an explicit segment size (bufferSize). The second approach creates an empty instance and copies a file stream into it. The constructor's second parameter (bufferSize) is optional and defaults to 1,000,000 bytes (1 MB). You can omit it unless you want a different segment size.
PdfFormatProvider pdfFormatProvider = new PdfFormatProvider();
RadFixedDocument radFixedDocument1;
RadFixedDocument radFixedDocument2;
string inputPath = "large.pdf";
// Method 1: Load from byte array (explicit bufferSize provided; could be omitted because 1,000,000 is the default)
byte[] byteArray = File.ReadAllBytes(inputPath);
using (ExpandableMemoryStream expandableMemoryStream = new ExpandableMemoryStream(byteArray, 1_000_000))
{
radFixedDocument1 = pdfFormatProvider.Import(expandableMemoryStream, TimeSpan.FromSeconds(120));
// ... manipulate radFixedDocument1 ...
}
// Method 2: Load by copying from FileStream (will use default buffer size when not specified)
using (ExpandableMemoryStream expandableMemoryStream = new ExpandableMemoryStream())
{
using (FileStream fileStream = File.OpenRead(inputPath))
{
fileStream.CopyTo(expandableMemoryStream);
}
expandableMemoryStream.Position = 0; // Reset before import
radFixedDocument2 = pdfFormatProvider.Import(expandableMemoryStream, TimeSpan.FromSeconds(120));
// ... manipulate radFixedDocument2 ...
}
In both cases the segmented internal structure avoids reallocating a single large contiguous buffer, helping performance and memory stability for very large PDF files.