internal MemoryMappedViewAccessor(MemoryMappedView view)
{
Debug.Assert(view != null, "view is null");
_view = view;
Initialize(_view.ViewHandle, _view.PointerOffset, _view.Size, MemoryMappedFile.GetFileAccess(_view.Access));
}
public MemoryMappedViewStream CreateViewStream(Int64 offset, Int64 size, MemoryMappedFileAccess access)
{
if (offset < 0)
{
throw new ArgumentOutOfRangeException("offset", SR.GetString(SR.ArgumentOutOfRange_NeedNonNegNum));
}
if (size < 0)
{
throw new ArgumentOutOfRangeException("size", SR.GetString(SR.ArgumentOutOfRange_PositiveOrDefaultSizeRequired));
}
if (access < MemoryMappedFileAccess.ReadWrite || access > MemoryMappedFileAccess.ReadWriteExecute)
{
throw new ArgumentOutOfRangeException("access");
}
if (IntPtr.Size == 4 && size > UInt32.MaxValue)
{
throw new ArgumentOutOfRangeException("size", SR.GetString(SR.ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed));
}
MemoryMappedView view = MemoryMappedView.CreateView(_handle, access, offset, size);
return(new MemoryMappedViewStream(view));
}
public MemoryMappedViewAccessor CreateViewAccessor(long offset, long size, MemoryMappedFileAccess access)
{
if (offset < 0)
{
throw new ArgumentOutOfRangeException(nameof(offset), SR.ArgumentOutOfRange_NeedNonNegNum);
}
if (size < 0)
{
throw new ArgumentOutOfRangeException(nameof(size), SR.ArgumentOutOfRange_PositiveOrDefaultSizeRequired);
}
if (access < MemoryMappedFileAccess.ReadWrite || access > MemoryMappedFileAccess.ReadWriteExecute)
{
throw new ArgumentOutOfRangeException(nameof(access));
}
if (IntPtr.Size == 4 && size > uint.MaxValue)
{
throw new ArgumentOutOfRangeException(nameof(size), SR.ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed);
}
MemoryMappedView view = MemoryMappedView.CreateView(_handle, access, offset, size);
return(new MemoryMappedViewAccessor(view));
}
internal MemoryMappedViewStream(MemoryMappedView view)
{
Debug.Assert(view != null, "view is null");
_view = view;
Initialize(_view.ViewHandle, _view.PointerOffset, _view.Size, MemoryMappedFile.GetFileAccess(_view.Access));
}
private void Dispose(bool disposeManagedResources)
{
if (_view != null)
{
_view.Dispose();
}
_view = null;
}
private static unsafe SafeMemoryMappedFileHandle CreateCore(
FileStream fileStream, string mapName,
HandleInheritability inheritability, MemoryMappedFileAccess access,
MemoryMappedFileOptions options, long capacity)
{
if (mapName != null)
{
// Named maps are not supported in our Unix implementation. We could support named maps on Linux using
// shared memory segments (shmget/shmat/shmdt/shmctl/etc.), but that doesn't work on OSX by default due
// to very low default limits on OSX for the size of such objects; it also doesn't support behaviors
// like copy-on-write or the ability to control handle inheritability, and reliably cleaning them up
// relies on some non-conforming behaviors around shared memory IDs remaining valid even after they've
// been marked for deletion (IPC_RMID). We could also support named maps using the current implementation
// by not unlinking after creating the backing store, but then the backing stores would remain around
// and accessible even after process exit, with no good way to appropriately clean them up.
// (File-backed maps may still be used for cross-process communication.)
throw CreateNamedMapsNotSupportedException();
}
bool ownsFileStream = false;
if (fileStream != null)
{
// This map is backed by a file. Make sure the file's size is increased to be
// at least as big as the requested capacity of the map.
if (fileStream.Length < capacity)
{
fileStream.SetLength(capacity);
}
}
else
{
// This map is backed by memory-only. With files, multiple views over the same map
// will end up being able to share data through the same file-based backing store;
// for anonymous maps, we need a similar backing store, or else multiple views would logically
// each be their own map and wouldn't share any data. To achieve this, we create a backing object
// (either memory or on disk, depending on the system) and use its file descriptor as the file handle.
// However, we only do this when the permission is more than read-only. We can't change the size
// of an object that has read-only permissions, but we also don't need to worry about sharing
// views over a read-only, anonymous, memory-backed map, because the data will never change, so all views
// will always see zero and can't change that. In that case, we just use the built-in anonymous support of
// the map by leaving fileStream as null.
Interop.libc.MemoryMappedProtections protections = MemoryMappedView.GetProtections(access, forVerification: false);
if ((protections & Interop.libc.MemoryMappedProtections.PROT_WRITE) != 0 && capacity > 0)
{
ownsFileStream = true;
fileStream = CreateSharedBackingObject(protections, capacity);
}
}
return(new SafeMemoryMappedFileHandle(fileStream, ownsFileStream, inheritability, access, options, capacity));
}
private static unsafe SafeMemoryMappedFileHandle CreateCore(
FileStream fileStream, string mapName,
HandleInheritability inheritability, MemoryMappedFileAccess access,
MemoryMappedFileOptions options, long capacity)
{
if (mapName != null)
{
// TODO: We currently do not support named maps. We could possibly support
// named maps in the future by using shm_open / shm_unlink, as we do for
// giving internal names to anonymous maps. Issues to work through will include
// dealing with permissions, passing information from the creator of the
// map to another opener of it, etc.
throw CreateNamedMapsNotSupportedException();
}
SafeFileHandle fileHandle = null;
if (fileStream != null)
{
// This map is backed by a file. Make sure the file's size is increased to be
// at least as big as the requested capacity of the map.
fileHandle = fileStream.SafeFileHandle;
if (fileStream.Length < capacity)
{
fileStream.SetLength(capacity);
}
}
else
{
// This map is backed by memory-only. With files, multiple views over the same map
// will end up being able to share data through the same file-based backing store;
// for anonymous maps, we need a similar backing store, or else multiple views would logically
// each be their own map and wouldn't share any data. To achieve this, we create a POSIX shared
// memory object and use its file descriptor as the file handle. However, we only do this when the
// permission is more than read-only. We can't ftruncate to increase the size of a shared memory
// object that has read-only permissions, but we also don't need to worry about sharing
// views over a read-only, anonymous, memory-backed map, because the data will never change, so all views
// will always see zero and can't change that. In that case, we just use the built-in anonymous support of
// the map by leaving fileHandle as null.
Interop.libc.MemoryMappedProtections protections = MemoryMappedView.GetProtections(access, forVerification: false);
if ((protections & Interop.libc.MemoryMappedProtections.PROT_WRITE) != 0 && capacity > 0)
{
mapName = "/AnonCoreFxMemMap_" + Guid.NewGuid().ToString("N"); // unique name must start with "/" and be < NAME_MAX length
fileHandle = CreateNewSharedMemoryObject(mapName, protections, capacity);
}
}
return(new SafeMemoryMappedFileHandle(mapName, fileHandle, inheritability, access, options, capacity));
}
public MemoryMappedViewAccessor CreateViewAccessor(long offset, long size, MemoryMappedFileAccess access = MemoryMappedFileAccess.ReadWrite)
{
if (offset < 0)
{
throw new ArgumentOutOfRangeException("offset", "Value must be non-negative");
}
if (size < 0)
{
throw new ArgumentOutOfRangeException("size", "Value must be positive or zero for default size");
}
if (IntPtr.Size == 4 && size > ((1024 * 1024 * 1024) * (long)4))
{
throw new ArgumentOutOfRangeException("size", "The capacity cannot be greater than the size of the system's logical address space.");
}
MemoryMappedView memoryMappedView = MemoryMappedView.CreateView(this._handle, access, offset, size);
return(new MemoryMappedViewAccessor(memoryMappedView));
}
public MemoryMappedViewStream CreateViewStream(long offset, long size, MemoryMappedFileAccess access)
{
if (offset < 0L)
{
throw new ArgumentOutOfRangeException("offset", System.SR.GetString("ArgumentOutOfRange_NeedNonNegNum"));
}
if (size < 0L)
{
throw new ArgumentOutOfRangeException("size", System.SR.GetString("ArgumentOutOfRange_PositiveOrDefaultSizeRequired"));
}
if ((access < MemoryMappedFileAccess.ReadWrite) || (access > MemoryMappedFileAccess.ReadWriteExecute))
{
throw new ArgumentOutOfRangeException("access");
}
if ((IntPtr.Size == 4) && (size > 0xffffffffL))
{
throw new ArgumentOutOfRangeException("size", System.SR.GetString("ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed"));
}
return(new MemoryMappedViewStream(MemoryMappedView.CreateView(this._handle, access, offset, size)));
}
internal unsafe MemoryMappedViewStream(MemoryMappedView view) {
Debug.Assert(view != null, "view is null");
m_view = view;
Initialize(m_view.ViewHandle, m_view.PointerOffset, m_view.Size, MemoryMappedFile.GetFileAccess(m_view.Access));
}
internal unsafe static MemoryMappedView CreateView(SafeMemoryMappedFileHandle memMappedFileHandle,
MemoryMappedFileAccess access, Int64 offset, Int64 size) {
// MapViewOfFile can only create views that start at a multiple of the system memory allocation
// granularity. We decided to hide this restriction form the user by creating larger views than the
// user requested and hiding the parts that the user did not request. extraMemNeeded is the amount of
// extra memory we allocate before the start of the requested view. MapViewOfFile will also round the
// capacity of the view to the nearest multiple of the system page size. Once again, we hide this
// from the user by preventing them from writing to any memory that they did not request.
ulong extraMemNeeded = (ulong)offset % (ulong)MemoryMappedFile.GetSystemPageAllocationGranularity();
// newOffset takes into account the fact that we have some extra memory allocated before the requested view
ulong newOffset = (ulong)offset - extraMemNeeded;
Debug.Assert(newOffset >= 0, "newOffset = (offset - extraMemNeeded) < 0");
// determine size to pass to MapViewOfFile
ulong nativeSize;
if (size != MemoryMappedFile.DefaultSize) {
nativeSize = (ulong)size + (ulong)extraMemNeeded;
}
else {
nativeSize = 0;
}
if (IntPtr.Size == 4 && nativeSize > UInt32.MaxValue) {
throw new ArgumentOutOfRangeException("size", SR.GetString(SR.ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed));
}
// if request is >= than total virtual, then MapViewOfFile will fail with meaningless error message
// "the parameter is incorrect"; this provides better error message in advance
UnsafeNativeMethods.MEMORYSTATUSEX memStatus = new UnsafeNativeMethods.MEMORYSTATUSEX();
bool result = UnsafeNativeMethods.GlobalMemoryStatusEx(ref memStatus);
ulong totalVirtual = memStatus.ullTotalVirtual;
if (nativeSize >= totalVirtual) {
throw new IOException(SR.GetString(SR.IO_NotEnoughMemory));
}
// split the Int64 into two ints
uint offsetLow = (uint)(newOffset & 0x00000000FFFFFFFFL);
uint offsetHigh = (uint)(newOffset >> 32);
// create the view
SafeMemoryMappedViewHandle viewHandle = UnsafeNativeMethods.MapViewOfFile(memMappedFileHandle,
MemoryMappedFile.GetFileMapAccess(access), offsetHigh, offsetLow, new UIntPtr(nativeSize));
if (viewHandle.IsInvalid) {
__Error.WinIOError(Marshal.GetLastWin32Error(), String.Empty);
}
// Query the view for its size and allocation type
UnsafeNativeMethods.MEMORY_BASIC_INFORMATION viewInfo = new UnsafeNativeMethods.MEMORY_BASIC_INFORMATION();
UnsafeNativeMethods.VirtualQuery(viewHandle, ref viewInfo, (IntPtr)Marshal.SizeOf(viewInfo));
ulong viewSize = (ulong)viewInfo.RegionSize;
// Allocate the pages if we were using the MemoryMappedFileOptions.DelayAllocatePages option
// OR check if the allocated view size is smaller than the expected native size
// If multiple overlapping views are created over the file mapping object, the pages in a given region
// could have different attributes(MEM_RESERVE OR MEM_COMMIT) as MapViewOfFile preserves coherence between
// views created on a mapping object backed by same file.
// In which case, the viewSize will be smaller than nativeSize required and viewState could be MEM_COMMIT
// but more pages may need to be committed in the region.
// This is because, VirtualQuery function(that internally invokes VirtualQueryEx function) returns the attributes
// and size of the region of pages with matching attributes starting from base address.
// VirtualQueryEx: http://msdn.microsoft.com/en-us/library/windows/desktop/aa366907(v=vs.85).aspx
if (((viewInfo.State & UnsafeNativeMethods.MEM_RESERVE) != 0) || (viewSize < nativeSize)) {
ulong allocSize = (nativeSize == 0) ? viewSize : nativeSize;
IntPtr tempHandle = UnsafeNativeMethods.VirtualAlloc(viewHandle, (UIntPtr)allocSize, UnsafeNativeMethods.MEM_COMMIT,
MemoryMappedFile.GetPageAccess(access));
int lastError = Marshal.GetLastWin32Error();
// The following is commented out for backward compatibility.
// Previously releases failed to check for this error so introducing this check
// could cause new/different exceptions in existing code paths.
// if (tempHandle == IntPtr.Zero) {
// __Error.WinIOError(lastError, String.Empty);
// }
// again query the view for its new size
viewInfo = new UnsafeNativeMethods.MEMORY_BASIC_INFORMATION();
UnsafeNativeMethods.VirtualQuery(viewHandle, ref viewInfo, (IntPtr)Marshal.SizeOf(viewInfo));
viewSize = (ulong)viewInfo.RegionSize;
}
// if the user specified DefaultSize as the size, we need to get the actual size
if (size == MemoryMappedFile.DefaultSize) {
size = (Int64)(viewSize - extraMemNeeded);
}
else {
Debug.Assert(viewSize >= (ulong)size, "viewSize < size");
}
viewHandle.Initialize((ulong)size + extraMemNeeded);
MemoryMappedView mmv = new MemoryMappedView(viewHandle, (long)extraMemNeeded, size, access);
return mmv;
}
internal unsafe static MemoryMappedView CreateView(SafeMemoryMappedFileHandle memMappedFileHandle,
MemoryMappedFileAccess access, Int64 offset, Int64 size)
{
// MapViewOfFile can only create views that start at a multiple of the system memory allocation
// granularity. We decided to hide this restriction form the user by creating larger views than the
// user requested and hiding the parts that the user did not request. extraMemNeeded is the amount of
// extra memory we allocate before the start of the requested view. MapViewOfFile will also round the
// capacity of the view to the nearest multiple of the system page size. Once again, we hide this
// from the user by preventing them from writing to any memory that they did not request.
ulong extraMemNeeded = (ulong)offset % (ulong)MemoryMappedFile.GetSystemPageAllocationGranularity();
// newOffset takes into account the fact that we have some extra memory allocated before the requested view
ulong newOffset = (ulong)offset - extraMemNeeded;
Debug.Assert(newOffset >= 0, "newOffset = (offset - extraMemNeeded) < 0");
// determine size to pass to MapViewOfFile
ulong nativeSize;
if (size != MemoryMappedFile.DefaultSize)
{
nativeSize = (ulong)size + (ulong)extraMemNeeded;
}
else
{
nativeSize = 0;
}
if (IntPtr.Size == 4 && nativeSize > UInt32.MaxValue)
{
throw new ArgumentOutOfRangeException("size", SR.GetString(SR.ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed));
}
// if request is >= than total virtual, then MapViewOfFile will fail with meaningless error message
// "the parameter is incorrect"; this provides better error message in advance
UnsafeNativeMethods.MEMORYSTATUSEX memStatus = new UnsafeNativeMethods.MEMORYSTATUSEX();
bool result = UnsafeNativeMethods.GlobalMemoryStatusEx(ref memStatus);
ulong totalVirtual = memStatus.ullTotalVirtual;
if (nativeSize >= totalVirtual)
{
throw new IOException(SR.GetString(SR.IO_NotEnoughMemory));
}
// split the Int64 into two ints
uint offsetLow = (uint)(newOffset & 0x00000000FFFFFFFFL);
uint offsetHigh = (uint)(newOffset >> 32);
// create the view
SafeMemoryMappedViewHandle viewHandle = UnsafeNativeMethods.MapViewOfFile(memMappedFileHandle,
MemoryMappedFile.GetFileMapAccess(access), offsetHigh, offsetLow, new UIntPtr(nativeSize));
if (viewHandle.IsInvalid)
{
__Error.WinIOError(Marshal.GetLastWin32Error(), String.Empty);
}
// Query the view for its size and allocation type
UnsafeNativeMethods.MEMORY_BASIC_INFORMATION viewInfo = new UnsafeNativeMethods.MEMORY_BASIC_INFORMATION();
UnsafeNativeMethods.VirtualQuery(viewHandle, ref viewInfo, (IntPtr)Marshal.SizeOf(viewInfo));
ulong viewSize = (ulong)viewInfo.RegionSize;
// Allocate the pages if we were using the MemoryMappedFileOptions.DelayAllocatePages option
// OR check if the allocated view size is smaller than the expected native size
// If multiple overlapping views are created over the file mapping object, the pages in a given region
// could have different attributes(MEM_RESERVE OR MEM_COMMIT) as MapViewOfFile preserves coherence between
// views created on a mapping object backed by same file.
// In which case, the viewSize will be smaller than nativeSize required and viewState could be MEM_COMMIT
// but more pages may need to be committed in the region.
// This is because, VirtualQuery function(that internally invokes VirtualQueryEx function) returns the attributes
// and size of the region of pages with matching attributes starting from base address.
// VirtualQueryEx: http://msdn.microsoft.com/en-us/library/windows/desktop/aa366907(v=vs.85).aspx
if (((viewInfo.State & UnsafeNativeMethods.MEM_RESERVE) != 0) || (viewSize < nativeSize))
{
ulong allocSize = (nativeSize == 0) ? viewSize : nativeSize;
IntPtr tempHandle = UnsafeNativeMethods.VirtualAlloc(viewHandle, (UIntPtr)allocSize, UnsafeNativeMethods.MEM_COMMIT,
MemoryMappedFile.GetPageAccess(access));
int lastError = Marshal.GetLastWin32Error();
// The following is commented out for backward compatibility.
// Previously releases failed to check for this error so introducing this check
// could cause new/different exceptions in existing code paths.
// if (tempHandle == IntPtr.Zero) {
// __Error.WinIOError(lastError, String.Empty);
// }
// again query the view for its new size
viewInfo = new UnsafeNativeMethods.MEMORY_BASIC_INFORMATION();
UnsafeNativeMethods.VirtualQuery(viewHandle, ref viewInfo, (IntPtr)Marshal.SizeOf(viewInfo));
viewSize = (ulong)viewInfo.RegionSize;
}
// if the user specified DefaultSize as the size, we need to get the actual size
if (size == MemoryMappedFile.DefaultSize)
{
size = (Int64)(viewSize - extraMemNeeded);
}
else
{
Debug.Assert(viewSize >= (ulong)size, "viewSize < size");
}
viewHandle.Initialize((ulong)size + extraMemNeeded);
MemoryMappedView mmv = new MemoryMappedView(viewHandle, (long)extraMemNeeded, size, access);
return(mmv);
}
public MemoryMappedViewAccessor CreateViewAccessor(long offset, long size, MemoryMappedFileAccess access)
{
var view = MemoryMappedView.Create(handle, offset, size, access);
return(new MemoryMappedViewAccessor(view));
}
public MemoryMappedViewStream CreateViewStream(long offset, long size, MemoryMappedFileAccess access)
{
var view = MemoryMappedView.Create(handle.DangerousGetHandle(), offset, size, access);
return(new MemoryMappedViewStream(view));
}
internal MemoryMappedViewAccessor(MemoryMappedView view)
{
this.m_view = view;
base.Initialize(this.m_view.ViewHandle, this.m_view.PointerOffset, this.m_view.Size, MemoryMappedFile.GetFileAccess(this.m_view.Access));
}
internal unsafe static MemoryMappedView CreateView(SafeMemoryMappedFileHandle memMappedFileHandle,
MemoryMappedFileAccess access, Int64 offset, Int64 size)
{
// MapViewOfFile can only create views that start at a multiple of the system memory allocation
// granularity. We decided to hide this restriction form the user by creating larger views than the
// user requested and hiding the parts that the user did not request. extraMemNeeded is the amount of
// extra memory we allocate before the start of the requested view. MapViewOfFile will also round the
// capacity of the view to the nearest multiple of the system page size. Once again, we hide this
// from the user by preventing them from writing to any memory that they did not request.
ulong extraMemNeeded = (ulong)offset % (ulong)MemoryMappedFile.GetSystemPageAllocationGranularity();
// newOffset takes into account the fact that we have some extra memory allocated before the requested view
ulong newOffset = (ulong)offset - extraMemNeeded;
Debug.Assert(newOffset >= 0, "newOffset = (offset - extraMemNeeded) < 0");
// determine size to pass to MapViewOfFile
ulong nativeSize;
if (size != MemoryMappedFile.DefaultSize)
{
nativeSize = (ulong)size + (ulong)extraMemNeeded;
}
else
{
nativeSize = 0;
}
if (IntPtr.Size == 4 && nativeSize > UInt32.MaxValue)
{
throw new ArgumentOutOfRangeException("size", SR.GetString(SR.ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed));
}
// if request is >= than total virtual, then MapViewOfFile will fail with meaningless error message
// "the parameter is incorrect"; this provides better error message in advance
UnsafeNativeMethods.MEMORYSTATUSEX memStatus = new UnsafeNativeMethods.MEMORYSTATUSEX();
bool result = UnsafeNativeMethods.GlobalMemoryStatusEx(memStatus);
ulong totalVirtual = memStatus.ullTotalVirtual;
if (nativeSize >= totalVirtual)
{
throw new IOException(SR.GetString(SR.IO_NotEnoughMemory));
}
// split the Int64 into two ints
uint offsetLow = (uint)(newOffset & 0x00000000FFFFFFFFL);
uint offsetHigh = (uint)(newOffset >> 32);
// create the view
SafeMemoryMappedViewHandle viewHandle = UnsafeNativeMethods.MapViewOfFile(memMappedFileHandle,
MemoryMappedFile.GetFileMapAccess(access), offsetHigh, offsetLow, new UIntPtr(nativeSize));
if (viewHandle.IsInvalid)
{
__Error.WinIOError(Marshal.GetLastWin32Error(), String.Empty);
}
// Query the view for its size and allocation type
UnsafeNativeMethods.MEMORY_BASIC_INFORMATION viewInfo = new UnsafeNativeMethods.MEMORY_BASIC_INFORMATION();
UnsafeNativeMethods.VirtualQuery(viewHandle, ref viewInfo, (IntPtr)Marshal.SizeOf(viewInfo));
ulong viewSize = (ulong)viewInfo.RegionSize;
// allocate the pages if we were using the MemoryMappedFileOptions.DelayAllocatePages option
if ((viewInfo.State & UnsafeNativeMethods.MEM_RESERVE) != 0)
{
IntPtr tempHandle = UnsafeNativeMethods.VirtualAlloc(viewHandle, (UIntPtr)viewSize, UnsafeNativeMethods.MEM_COMMIT,
MemoryMappedFile.GetPageAccess(access));
int lastError = Marshal.GetLastWin32Error();
if (viewHandle.IsInvalid)
{
__Error.WinIOError(lastError, String.Empty);
}
}
// if the user specified DefaultSize as the size, we need to get the actual size
if (size == MemoryMappedFile.DefaultSize)
{
size = (Int64)(viewSize - extraMemNeeded);
}
else
{
Debug.Assert(viewSize >= (ulong)size, "viewSize < size");
}
viewHandle.Initialize((ulong)size + extraMemNeeded);
MemoryMappedView mmv = new MemoryMappedView(viewHandle, (long)extraMemNeeded, size, access);
return(mmv);
}
internal MemoryMappedViewAccessor(MemoryMappedView view)
{
this.m_view = view;
base.Initialize(this.m_view.ViewHandle, this.m_view.PointerOffset, this.m_view.Size, MemoryMappedFile.GetFileAccess(this.m_view.Access));
}
internal MemoryMappedViewAccessor(MemoryMappedView memoryMappedView)
{
this._view = memoryMappedView;
}
internal unsafe static MemoryMappedView CreateView(SafeMemoryMappedFileHandle memMappedFileHandle,
MemoryMappedFileAccess access, Int64 offset, Int64 size) {
// MapViewOfFile can only create views that start at a multiple of the system memory allocation
// granularity. We decided to hide this restriction form the user by creating larger views than the
// user requested and hiding the parts that the user did not request. extraMemNeeded is the amount of
// extra memory we allocate before the start of the requested view. MapViewOfFile will also round the
// capacity of the view to the nearest multiple of the system page size. Once again, we hide this
// from the user by preventing them from writing to any memory that they did not request.
ulong extraMemNeeded = (ulong)offset % (ulong)MemoryMappedFile.GetSystemPageAllocationGranularity();
// newOffset takes into account the fact that we have some extra memory allocated before the requested view
ulong newOffset = (ulong)offset - extraMemNeeded;
Debug.Assert(newOffset >= 0, "newOffset = (offset - extraMemNeeded) < 0");
// determine size to pass to MapViewOfFile
ulong nativeSize;
if (size != MemoryMappedFile.DefaultSize) {
nativeSize = (ulong)size + (ulong)extraMemNeeded;
}
else {
nativeSize = 0;
}
if (IntPtr.Size == 4 && nativeSize > UInt32.MaxValue) {
throw new ArgumentOutOfRangeException("size", SR.GetString(SR.ArgumentOutOfRange_CapacityLargerThanLogicalAddressSpaceNotAllowed));
}
// if request is >= than total virtual, then MapViewOfFile will fail with meaningless error message
// "the parameter is incorrect"; this provides better error message in advance
UnsafeNativeMethods.MEMORYSTATUSEX memStatus = new UnsafeNativeMethods.MEMORYSTATUSEX();
bool result = UnsafeNativeMethods.GlobalMemoryStatusEx(memStatus);
ulong totalVirtual = memStatus.ullTotalVirtual;
if (nativeSize >= totalVirtual) {
throw new IOException(SR.GetString(SR.IO_NotEnoughMemory));
}
// split the Int64 into two ints
uint offsetLow = (uint)(newOffset & 0x00000000FFFFFFFFL);
uint offsetHigh = (uint)(newOffset >> 32);
// create the view
SafeMemoryMappedViewHandle viewHandle = UnsafeNativeMethods.MapViewOfFile(memMappedFileHandle,
MemoryMappedFile.GetFileMapAccess(access), offsetHigh, offsetLow, new UIntPtr(nativeSize));
if (viewHandle.IsInvalid) {
__Error.WinIOError(Marshal.GetLastWin32Error(), String.Empty);
}
// Query the view for its size and allocation type
UnsafeNativeMethods.MEMORY_BASIC_INFORMATION viewInfo = new UnsafeNativeMethods.MEMORY_BASIC_INFORMATION();
UnsafeNativeMethods.VirtualQuery(viewHandle, ref viewInfo, (IntPtr)Marshal.SizeOf(viewInfo));
ulong viewSize = (ulong)viewInfo.RegionSize;
// allocate the pages if we were using the MemoryMappedFileOptions.DelayAllocatePages option
if ((viewInfo.State & UnsafeNativeMethods.MEM_RESERVE) != 0) {
IntPtr tempHandle = UnsafeNativeMethods.VirtualAlloc(viewHandle, (UIntPtr)viewSize, UnsafeNativeMethods.MEM_COMMIT,
MemoryMappedFile.GetPageAccess(access));
int lastError = Marshal.GetLastWin32Error();
if (viewHandle.IsInvalid) {
__Error.WinIOError(lastError, String.Empty);
}
}
// if the user specified DefaultSize as the size, we need to get the actual size
if (size == MemoryMappedFile.DefaultSize) {
size = (Int64)(viewSize - extraMemNeeded);
}
else {
Debug.Assert(viewSize >= (ulong)size, "viewSize < size");
}
viewHandle.Initialize((ulong)size + extraMemNeeded);
MemoryMappedView mmv = new MemoryMappedView(viewHandle, (long)extraMemNeeded, size, access);
return mmv;
}
