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// ==++==
//
// Copyright (c) Microsoft Corporation. All rights reserved.
//
// ==--==
/*============================================================
**
** Purpose: Unsafe code that uses pointers should use
** SafePointer to fix subtle lifetime problems with the
** underlying resource.
**
===========================================================*/
// Design points:
// *) Avoid handle-recycling problems (including ones triggered via
// resurrection attacks) for all accesses via pointers. This requires tying
// together the lifetime of the unmanaged resource with the code that reads
// from that resource, in a package that uses synchronization to enforce
// the correct semantics during finalization. We're using SafeHandle's
// ref count as a gate on whether the pointer can be dereferenced because that
// controls the lifetime of the resource.
//
// *) Keep the penalties for using this class small, both in terms of space
// and time. Having multiple threads reading from a memory mapped file
// will already require 2 additional interlocked operations. If we add in
// a "current position" concept, that requires additional space in memory and
// synchronization. Since the position in memory is often (but not always)
// something that can be stored on the stack, we can save some memory by
// excluding it from this object. However, avoiding the need for
// synchronization is a more significant win. This design allows multiple
// threads to read and write memory simultaneously without locks (as long as
// you don't write to a region of memory that overlaps with what another
// thread is accessing).
//
// *) Space-wise, we use the following memory, including SafeHandle's fields:
// Object Header MT* handle int bool bool <2 pad bytes> length
// On 32 bit platforms: 24 bytes. On 64 bit platforms: 40 bytes.
// (We can safe 4 bytes on x86 only by shrinking SafeHandle)
//
// *) Wrapping a SafeHandle would have been a nice solution, but without an
// ordering between critical finalizable objects, it would have required
// changes to each SafeHandle subclass to opt in to being usable from a
// SafeBuffer (or some clever exposure of SafeHandle's state fields and a
// way of forcing ReleaseHandle to run even after the SafeHandle has been
// finalized with a ref count > 1). We can use less memory and create fewer
// objects by simply inserting a SafeBuffer into the class hierarchy.
//
// *) In an ideal world, we could get marshaling support for SafeBuffer that
// would allow us to annotate a P/Invoke declaration, saying this parameter
// specifies the length of the buffer, and the units of that length are X.
// P/Invoke would then pass that size parameter to SafeBuffer.
// [DllImport(...)]
// static extern SafeMemoryHandle AllocCharBuffer(int numChars);
// If we could put an attribute on the SafeMemoryHandle saying numChars is
// the element length, and it must be multiplied by 2 to get to the byte
// length, we can simplify the usage model for SafeBuffer.
//
// *) This class could benefit from a constraint saying T is a value type
// containing no GC references.
// Implementation notes:
// *) The Initialize method must be called before you use any instance of
// a SafeBuffer. To avoid ----s when storing SafeBuffers in statics,
// you either need to take a lock when publishing the SafeBuffer, or you
// need to create a local, initialize the SafeBuffer, then assign to the
// static variable (perhaps using Interlocked.CompareExchange). Of course,
// assignments in a static class constructor are under a lock implicitly.
namespace System.Runtime.InteropServices
{
using System;
using System.Security.Permissions;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;
using System.Runtime.ConstrainedExecution;
using System.Runtime.Versioning;
using Microsoft.Win32.SafeHandles;
using System.Diagnostics.Contracts;
[System.Security.SecurityCritical]
public abstract unsafe class SafeBuffer : SafeHandleZeroOrMinusOneIsInvalid
{
// Steal UIntPtr.MaxValue as our uninitialized value.
private static readonly UIntPtr Uninitialized = (UIntPtr.Size == 4) ?
((UIntPtr) UInt32.MaxValue) : ((UIntPtr) UInt64.MaxValue);
private UIntPtr _numBytes;
protected SafeBuffer(bool ownsHandle) : base(ownsHandle)
{
_numBytes = Uninitialized;
}
/// <summary>
/// Specifies the size of the region of memory, in bytes. Must be
/// called before using the SafeBuffer.
/// </summary>
/// <param name="numBytes">Number of valid bytes in memory.</param>
[CLSCompliant(false)]
public void Initialize(ulong numBytes)
{
if (numBytes < 0)
throw new ArgumentOutOfRangeException("numBytes", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (IntPtr.Size == 4 && numBytes > UInt32.MaxValue)
throw new ArgumentOutOfRangeException("numBytes", Environment.GetResourceString("ArgumentOutOfRange_AddressSpace"));
Contract.EndContractBlock();
if (numBytes >= (ulong)Uninitialized)
throw new ArgumentOutOfRangeException("numBytes", Environment.GetResourceString("ArgumentOutOfRange_UIntPtrMax-1"));
_numBytes = (UIntPtr) numBytes;
}
/// <summary>
/// Specifies the the size of the region in memory, as the number of
/// elements in an array. Must be called before using the SafeBuffer.
/// </summary>
[CLSCompliant(false)]
public void Initialize(uint numElements, uint sizeOfEachElement)
{
if (numElements < 0)
throw new ArgumentOutOfRangeException("numElements", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (sizeOfEachElement < 0)
throw new ArgumentOutOfRangeException("sizeOfEachElement", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (IntPtr.Size == 4 && numElements * sizeOfEachElement > UInt32.MaxValue)
throw new ArgumentOutOfRangeException("numBytes", Environment.GetResourceString("ArgumentOutOfRange_AddressSpace"));
Contract.EndContractBlock();
if (numElements * sizeOfEachElement >= (ulong)Uninitialized)
throw new ArgumentOutOfRangeException("numElements", Environment.GetResourceString("ArgumentOutOfRange_UIntPtrMax-1"));
_numBytes = checked((UIntPtr) (numElements * sizeOfEachElement));
}
/// <summary>
/// Specifies the the size of the region in memory, as the number of
/// elements in an array. Must be called before using the SafeBuffer.
/// </summary>
[CLSCompliant(false)]
public void Initialize<T>(uint numElements) where T : struct
{
Initialize(numElements, Marshal.AlignedSizeOf<T>());
}
// Callers should ensure that they check whether the pointer ref param
// is null when AcquirePointer returns. If it is not null, they must
// call ReleasePointer in a CER. This method calls DangerousAddRef
// & exposes the pointer. Unlike Read, it does not alter the "current
// position" of the pointer. Here's how to use it:
//
// byte* pointer = null;
// RuntimeHelpers.PrepareConstrainedRegions();
// try {
// safeBuffer.AcquirePointer(ref pointer);
// // Use pointer here, with your own bounds checking
// }
// finally {
// if (pointer != null)
// safeBuffer.ReleasePointer();
// }
//
// Note: If you cast this byte* to a T*, you have to worry about
// whether your pointer is aligned. Additionally, you must take
// responsibility for all bounds checking with this pointer.
/// <summary>
/// Obtain the pointer from a SafeBuffer for a block of code,
/// with the express responsibility for bounds checking and calling
/// ReleasePointer later within a CER to ensure the pointer can be
/// freed later. This method either completes successfully or
/// throws an exception and returns with pointer set to null.
/// </summary>
/// <param name="pointer">A byte*, passed by reference, to receive
/// the pointer from within the SafeBuffer. You must set
/// pointer to null before calling this method.</param>
[CLSCompliant(false)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public void AcquirePointer(ref byte* pointer)
{
if (_numBytes == Uninitialized)
throw NotInitialized();
pointer = null;
RuntimeHelpers.PrepareConstrainedRegions();
try
{
}
finally
{
bool junk = false;
DangerousAddRef(ref junk);
pointer = (byte*)handle;
}
}
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
public void ReleasePointer()
{
if (_numBytes == Uninitialized)
throw NotInitialized();
DangerousRelease();
}
#if !FEATURE_CORECLR || FEATURE_CORESYSTEM
/// <summary>
/// Read a value type from memory at the given offset. This is
/// equivalent to: return *(T*)(bytePtr + byteOffset);
/// </summary>
/// <typeparam name="T">The value type to read</typeparam>
/// <param name="byteOffset">Where to start reading from memory. You
/// may have to consider alignment.</param>
/// <returns>An instance of T read from memory.</returns>
[CLSCompliant(false)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public T Read<T>(ulong byteOffset) where T : struct {
if (_numBytes == Uninitialized)
throw NotInitialized();
uint sizeofT = Marshal.SizeOfType(typeof(T));
byte* ptr = (byte*)handle + byteOffset;
SpaceCheck(ptr, sizeofT);
// return *(T*) (_ptr + byteOffset);
T value;
bool mustCallRelease = false;
RuntimeHelpers.PrepareConstrainedRegions();
try
{
DangerousAddRef(ref mustCallRelease);
GenericPtrToStructure<T>(ptr, out value, sizeofT);
}
finally
{
if (mustCallRelease)
DangerousRelease();
}
return value;
}
[CLSCompliant(false)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public void ReadArray<T>(ulong byteOffset, T[] array, int index, int count)
where T : struct
{
if (array == null)
throw new ArgumentNullException("array", Environment.GetResourceString("ArgumentNull_Buffer"));
if (index < 0)
throw new ArgumentOutOfRangeException("index", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (count < 0)
throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (array.Length - index < count)
throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
Contract.EndContractBlock();
if (_numBytes == Uninitialized)
throw NotInitialized();
uint sizeofT = Marshal.SizeOfType(typeof(T));
uint alignedSizeofT = Marshal.AlignedSizeOf<T>();
byte* ptr = (byte*)handle + byteOffset;
SpaceCheck(ptr, checked((ulong)(alignedSizeofT * count)));
bool mustCallRelease = false;
RuntimeHelpers.PrepareConstrainedRegions();
try
{
DangerousAddRef(ref mustCallRelease);
for (int i = 0; i < count; i++)
unsafe { GenericPtrToStructure<T>(ptr + alignedSizeofT * i, out array[i + index], sizeofT); }
}
finally
{
if (mustCallRelease)
DangerousRelease();
}
}
/// <summary>
/// Write a value type to memory at the given offset. This is
/// equivalent to: *(T*)(bytePtr + byteOffset) = value;
/// </summary>
/// <typeparam name="T">The type of the value type to write to memory.</typeparam>
/// <param name="byteOffset">The location in memory to write to. You
/// may have to consider alignment.</param>
/// <param name="value">The value type to write to memory.</param>
[CLSCompliant(false)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public void Write<T>(ulong byteOffset, T value) where T : struct {
if (_numBytes == Uninitialized)
throw NotInitialized();
uint sizeofT = Marshal.SizeOfType(typeof(T));
byte* ptr = (byte*)handle + byteOffset;
SpaceCheck(ptr, sizeofT);
// *((T*) (_ptr + byteOffset)) = value;
bool mustCallRelease = false;
RuntimeHelpers.PrepareConstrainedRegions();
try
{
DangerousAddRef(ref mustCallRelease);
GenericStructureToPtr(ref value, ptr, sizeofT);
}
finally
{
if (mustCallRelease)
DangerousRelease();
}
}
[CLSCompliant(false)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
public void WriteArray<T>(ulong byteOffset, T[] array, int index, int count)
where T : struct
{
if (array == null)
throw new ArgumentNullException("array", Environment.GetResourceString("ArgumentNull_Buffer"));
if (index < 0)
throw new ArgumentOutOfRangeException("index", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (count < 0)
throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
if (array.Length - index < count)
throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
Contract.EndContractBlock();
if (_numBytes == Uninitialized)
throw NotInitialized();
uint sizeofT = Marshal.SizeOfType(typeof(T));
uint alignedSizeofT = Marshal.AlignedSizeOf<T>();
byte* ptr = (byte*)handle + byteOffset;
SpaceCheck(ptr, checked((ulong)(alignedSizeofT * count)));
bool mustCallRelease = false;
RuntimeHelpers.PrepareConstrainedRegions();
try
{
DangerousAddRef(ref mustCallRelease);
for (int i = 0; i < count; i++)
unsafe { GenericStructureToPtr(ref array[i + index], ptr + alignedSizeofT * i, sizeofT); }
}
finally
{
if (mustCallRelease)
DangerousRelease();
}
}
#endif // !FEATURE_CORECLR || FEATURE_CORESYSTEM
/// <summary>
/// Returns the number of bytes in the memory region.
/// </summary>
[CLSCompliant(false)]
public ulong ByteLength {
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
get {
if (_numBytes == Uninitialized)
throw NotInitialized();
return (ulong) _numBytes;
}
}
/* No indexer. The perf would be misleadingly bad. People should use
* AcquirePointer and ReleasePointer instead. */
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
private void SpaceCheck(byte* ptr, ulong sizeInBytes)
{
if ((ulong)_numBytes < sizeInBytes)
NotEnoughRoom();
if ((ulong)(ptr - (byte*) handle) > ((ulong)_numBytes) - sizeInBytes)
NotEnoughRoom();
}
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
private static void NotEnoughRoom()
{
throw new ArgumentException(Environment.GetResourceString("Arg_BufferTooSmall"));
}
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
private static InvalidOperationException NotInitialized()
{
Contract.Assert(false, "Uninitialized SafeBuffer! Someone needs to call Initialize before using this instance!");
return new InvalidOperationException(Environment.GetResourceString("InvalidOperation_MustCallInitialize"));
}
// FCALL limitations mean we can't have generic FCALL methods. However, we can pass
// TypedReferences to FCALL methods.
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
internal static void GenericPtrToStructure<T>(byte* ptr, out T structure, uint sizeofT) where T : struct
{
structure = default(T); // Dummy assignment to silence the compiler
PtrToStructureNative(ptr, __makeref(structure), sizeofT);
}
[MethodImpl(MethodImplOptions.InternalCall)]
[ResourceExposure(ResourceScope.None)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
private static extern void PtrToStructureNative(byte* ptr, /*out T*/ TypedReference structure, uint sizeofT);
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
internal static void GenericStructureToPtr<T>(ref T structure, byte* ptr, uint sizeofT) where T : struct
{
StructureToPtrNative(__makeref(structure), ptr, sizeofT);
}
[MethodImpl(MethodImplOptions.InternalCall)]
[ResourceExposure(ResourceScope.None)]
[ReliabilityContract(Consistency.WillNotCorruptState, Cer.Success)]
private static extern void StructureToPtrNative(/*ref T*/ TypedReference structure, byte* ptr, uint sizeofT);
}
}
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