- 1 year ago
MemoryMappedFile has always the same size
In .NET, when using MemoryMappedFile
, the size of the mapped file remains constant once it is created. You cannot dynamically resize a MemoryMappedFile
after it has been created.
To work around this limitation, you can follow these steps:
- Create a new
MemoryMappedFile
with the desired initial size. - Use the
CreateViewAccessor
method of theMemoryMappedFile
to create aMemoryMappedViewAccessor
that provides read and write access to the mapped file. - Use the
MemoryMappedViewAccessor
to read and write data within the bounds of the initial size. - If you need to increase the size of the mapped file, you will need to create a new
MemoryMappedFile
with a larger size and copy the data from the oldMemoryMappedFile
to the new one.
Here's an example that demonstrates this approach:
csharpusing System;
using System.IO.MemoryMappedFiles;
class Program
{
static void Main()
{
const int initialSize = 1024; // Initial size of the mapped file
// Create a new memory-mapped file
using (MemoryMappedFile mmf = MemoryMappedFile.CreateNew("MyMemoryMappedFile", initialSize))
{
// Create a view accessor for read/write access
using (MemoryMappedViewAccessor accessor = mmf.CreateViewAccessor())
{
// Write data to the mapped file
byte[] data = { 1, 2, 3, 4, 5 };
accessor.WriteArray(0, data, 0, data.Length);
// Read data from the mapped file
byte[] readData = new byte[data.Length];
accessor.ReadArray(0, readData, 0, readData.Length);
Console.WriteLine("Read data: " + string.Join(", ", readData));
// Increase the size of the mapped file
int newSize = initialSize * 2;
using (MemoryMappedFile newMmf = MemoryMappedFile.CreateNew("MyNewMemoryMappedFile", newSize))
{
using (MemoryMappedViewAccessor newAccessor = newMmf.CreateViewAccessor())
{
// Copy data from the old mapped file to the new one
accessor.ReadArray(0, readData, 0, readData.Length);
newAccessor.WriteArray(0, readData, 0, readData.Length);
}
}
}
}
}
}
In the above example, we create a new MemoryMappedFile
with an initial size of 1024 bytes. We write data to the mapped file and then read it back. Later, we create a new MemoryMappedFile
with a larger size (double the initial size) and copy the data from the old mapped file to the new one.
Remember to handle exceptions, dispose of the MemoryMappedFile
and MemoryMappedViewAccessor
objects properly, and consider error handling and synchronization as necessary in your specific use case.