UnmanagedMemoryStream.cs source code in C# .NET

Source code for the .NET framework in C#

                        
Code:

                         / DotNET / DotNET / 8.0 / untmp / whidbey / REDBITS / ndp / clr / src / BCL / System / IO / UnmanagedMemoryStream.cs / 1 / UnmanagedMemoryStream.cs
                        

                        
                            // ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class:  UnmanagedMemoryStream 
**
** Purpose: Create a stream over unmanaged memory, mostly 
**          useful for memory-mapped files.
**
** Date:  October 20, 2000 (made public August 4, 2003)
** 
===========================================================*/
using System; 
using System.Runtime.InteropServices; 
using System.Security.Permissions;
 
namespace System.IO {

    /*
     * This class is used to access a contiguous block of memory, likely outside 
     * the GC heap (or pinned in place in the GC heap, but a MemoryStream may
     * make more sense in those cases).  It's great if you have a pointer and 
     * a length for a section of memory mapped in by someone else and you don't 
     * want to copy this into the GC heap.  UnmanagedMemoryStream assumes these
     * two things: 
     *
     * 1) All the memory in the specified block is readable or writable,
     *    depending on the values you pass to the constructor.
     * 2) The lifetime of the block of memory is at least as long as the lifetime 
     *    of the UnmanagedMemoryStream.
     * 3) You clean up the memory when appropriate.  The UnmanagedMemoryStream 
     *    currently will do NOTHING to free this memory. 
     * 4) All calls to Write and WriteByte may not be threadsafe currently.
     * 
     * It may become necessary to add in some sort of
     * DeallocationMode enum, specifying whether we unmap a section of memory,
     * call free, run a user-provided delegate to free the memory, etc etc.
     * We'll suggest user write a subclass of UnmanagedMemoryStream that uses 
     * a SafeHandle subclass to hold onto the memory.
     * Check for problems when using this in the negative parts of a 
     * process's address space.  We may need to use unsigned longs internally 
     * and change the overflow detection logic.
     */ 
    [CLSCompliant(false)]
    public class UnmanagedMemoryStream : Stream
    {
        // 

        private const long UnmanagedMemStreamMaxLength = Int64.MaxValue; 
 
        private unsafe byte* _mem;
        private long _length; 
        private long _capacity;
        private long _position;
        private FileAccess _access;
        internal bool _isOpen; 

        // Needed for subclasses that need to map a file, etc. 
        protected unsafe UnmanagedMemoryStream() 
        {
            _mem = null; 
            _isOpen = false;
        }

        public unsafe UnmanagedMemoryStream(byte* pointer, long length) 
        {
            Initialize(pointer, length, length, FileAccess.Read, false); 
        } 

        public unsafe UnmanagedMemoryStream(byte* pointer, long length, long capacity, FileAccess access) 
        {
            Initialize(pointer, length, capacity, access, false);
        }
 
        // We must create one of these without doing a security check.  This
        // class is created while security is trying to start up.  Plus, doing 
        // a Demand from Assembly.GetManifestResourceStream isn't useful. 
        internal unsafe UnmanagedMemoryStream(byte* pointer, long length, long capacity, FileAccess access, bool skipSecurityCheck)
        { 
            Initialize(pointer, length, capacity, access, skipSecurityCheck);
        }

        protected unsafe void Initialize(byte* pointer, long length, long capacity, FileAccess access) 
        {
            Initialize(pointer, length, capacity, access, false); 
        } 

        internal unsafe void Initialize(byte* pointer, long length, long capacity, FileAccess access, bool skipSecurityCheck) 
        {
            if (pointer == null)
                throw new ArgumentNullException("pointer");
            if (length < 0 || capacity < 0) 
                throw new ArgumentOutOfRangeException((length < 0) ? "length" : "capacity", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (length > capacity) 
                throw new ArgumentOutOfRangeException("length", Environment.GetResourceString("ArgumentOutOfRange_LengthGreaterThanCapacity")); 
            // Check for wraparound.
            if (((byte*) ((long)pointer + capacity)) < pointer) 
                throw new ArgumentOutOfRangeException("capacity", Environment.GetResourceString("ArgumentOutOfRange_UnmanagedMemStreamWrapAround"));
            if (access < FileAccess.Read || access > FileAccess.ReadWrite)
                throw new ArgumentOutOfRangeException("access", Environment.GetResourceString("ArgumentOutOfRange_Enum"));
            if (_isOpen) 
                throw new InvalidOperationException(Environment.GetResourceString("InvalidOperation_CalledTwice"));
 
            if (!skipSecurityCheck) 
                new SecurityPermission(SecurityPermissionFlag.UnmanagedCode).Demand();
 
            _mem = pointer;
            _length = length;
            _capacity = capacity;
            _access = access; 
            _isOpen = true;
        } 
 
        public override bool CanRead {
            get { return _isOpen && (_access & FileAccess.Read) != 0; } 
        }

        public override bool CanSeek {
            get { return _isOpen; } 
        }
 
        public override bool CanWrite { 
            get { return _isOpen && (_access & FileAccess.Write) != 0; }
        } 

        protected override void Dispose(bool disposing)
        {
            _isOpen = false; 
            //_mem = null;
 
            // Stream allocates WaitHandles for async calls. So for correctness 
            // call base.Dispose(disposing) for better perf, avoiding waiting
            // for the finalizers to run on those types. 
            base.Dispose(disposing);
        }

        public override void Flush() { 
            if (!_isOpen) __Error.StreamIsClosed();
        } 
 
        public override long Length {
            get { 
                if (!_isOpen) __Error.StreamIsClosed();
                return _length;
            }
        } 

        public long Capacity { 
            get { 
                if (!_isOpen) __Error.StreamIsClosed();
                return _capacity; 
            }
        }

        public unsafe override long Position { 
            get {
                if (!_isOpen) __Error.StreamIsClosed(); 
                return _position; 
            }
            set { 
                if (!_isOpen) __Error.StreamIsClosed();
                if (value < 0)
                    throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
 
#if WIN32
                // On 32 bit machines, ensure we don't wrap around. 
                if (value > (long) Int32.MaxValue || _mem + value < _mem) 
                    throw new ArgumentOutOfRangeException("value", Environment.GetResourceString("ArgumentOutOfRange_MemStreamLength"));
#endif 
                _position = value;
            }
        }
 
        public unsafe byte* PositionPointer {
            [SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] 
            get { 
                long pos = _position;  // Use a temp to avoid a race
                if (pos > _capacity) 
                    throw new IndexOutOfRangeException(Environment.GetResourceString("IndexOutOfRange_UMSPosition"));
                byte * ptr = _mem + pos;
                if (!_isOpen) __Error.StreamIsClosed();
                return ptr; 
            }
            [SecurityPermission(SecurityAction.LinkDemand, Flags=SecurityPermissionFlag.UnmanagedCode)] 
            set { 
                if (!_isOpen) __Error.StreamIsClosed();
                // Note: subtracting pointers returns an Int64.  Working around 
                // to avoid hitting compiler warning CS0652 on this line.
                if (new IntPtr(value - _mem).ToInt64() > UnmanagedMemStreamMaxLength)
                    throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_UnmanagedMemStreamLength"));
                if (value < _mem) 
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin"));
                _position = value - _mem; 
            } 
        }
 
        internal unsafe byte* Pointer {
            get {
                return _mem;
            } 
        }
 
        public override unsafe int Read([In, Out] byte[] buffer, int offset, int count) { 
            if (!_isOpen) __Error.StreamIsClosed();
            if ((_access & FileAccess.Read) == 0) __Error.ReadNotSupported(); 
            if (buffer==null)
                throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer"));
            if (offset < 0)
                throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum")); 
            if (count < 0)
                throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum")); 
            if (buffer.Length - offset < count) 
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen"));
 
            // Use a local variable to avoid a race where another thread
            // changes our position after we decide we can read some bytes.
            long pos = _position;
            long n = _length - pos; 
            if (n > count)
                n = count; 
            if (n <= 0) 
                return 0;
 
            int nInt = (int) n; // Safe because n <= count, which is an Int32
            if (nInt < 0)
                nInt = 0;  // _position could be beyond EOF
            BCLDebug.Assert(pos + nInt >= 0, "_position + n >= 0");  // len is less than 2^63 -1. 

            Buffer.memcpy(_mem + pos, 0, buffer, offset, nInt); 
            _position = pos + n; 
            return nInt;
        } 

        public override unsafe int ReadByte() {
            if (!_isOpen) __Error.StreamIsClosed();
            if ((_access & FileAccess.Read) == 0) __Error.ReadNotSupported(); 

            long pos = _position;  // Use a local to avoid a race condition 
            if (pos >= _length) 
                return -1;
            _position = pos + 1; 
            return _mem[pos];
        }

        public override unsafe long Seek(long offset, SeekOrigin loc) { 
            if (!_isOpen) __Error.StreamIsClosed();
            if (offset > UnmanagedMemStreamMaxLength) 
                throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_UnmanagedMemStreamLength")); 
            switch(loc) {
            case SeekOrigin.Begin: 
                if (offset < 0)
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin"));
                _position = offset;
                break; 

            case SeekOrigin.Current: 
                if (offset + _position < 0) 
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin"));
                _position += offset; 
                break;

            case SeekOrigin.End:
                if (_length + offset < 0) 
                    throw new IOException(Environment.GetResourceString("IO.IO_SeekBeforeBegin"));
                _position = _length + offset; 
                break; 

            default: 
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidSeekOrigin"));
            }

            BCLDebug.Assert(_position >= 0, "_position >= 0"); 
            return _position;
        } 
 
        public unsafe override void SetLength(long value) {
            if (!_isOpen) __Error.StreamIsClosed(); 
            if ((_access & FileAccess.Write) == 0) __Error.WriteNotSupported();
            if (value < 0)
                throw new ArgumentOutOfRangeException("length", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (value > _capacity) 
                throw new IOException(Environment.GetResourceString("IO.IO_FixedCapacity"));
 
            long len = _length; 
            if (value > len)
                Buffer.ZeroMemory(_mem+len, value-len); 
            _length = value;
            if (_position > value) _position = value;
        }
 
        public override unsafe void Write(byte[] buffer, int offset, int count) {
            if (!_isOpen) __Error.StreamIsClosed(); 
            if ((_access & FileAccess.Write) == 0) __Error.WriteNotSupported(); 
            if (buffer==null)
                throw new ArgumentNullException("buffer", Environment.GetResourceString("ArgumentNull_Buffer")); 
            if (offset < 0)
                throw new ArgumentOutOfRangeException("offset", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum"));
            if (count < 0)
                throw new ArgumentOutOfRangeException("count", Environment.GetResourceString("ArgumentOutOfRange_NeedNonNegNum")); 
            if (buffer.Length - offset < count)
                throw new ArgumentException(Environment.GetResourceString("Argument_InvalidOffLen")); 
 
            long pos = _position;  // Use a local to avoid a race condition
            long len = _length; 
            long n = pos + count;
            // Check for overflow
            if (n < 0)
                throw new IOException(Environment.GetResourceString("IO.IO_StreamTooLong")); 

            if (n > len) { 
                if (n > _capacity) 
                    throw new NotSupportedException(Environment.GetResourceString("IO.IO_FixedCapacity"));
                _length = n; 
            }
            // Check to see whether we are now expanding the stream and must
            // zero any memory in the middle.
            if (pos > len) 
                Buffer.ZeroMemory(_mem+len, pos-len);
 
            Buffer.memcpy(buffer, offset, _mem + pos, 0, count); 
            _position = n;
            return; 
        }

        public override unsafe void WriteByte(byte value) {
            if (!_isOpen) __Error.StreamIsClosed(); 
            if ((_access & FileAccess.Write) == 0) __Error.WriteNotSupported();
 
            long pos = _position;  // Use a local to avoid a race condition 
            long len = _length;
            long n = pos + 1; 
            if (pos >= len) {
                // Check for overflow
                if (n < 0)
                    throw new IOException(Environment.GetResourceString("IO.IO_StreamTooLong")); 

                if (n > _capacity) 
                    throw new NotSupportedException(Environment.GetResourceString("IO.IO_FixedCapacity")); 
                _length = n;
 
                // Check to see whether we are now expanding the stream and must
                // zero any memory in the middle.
                if (pos > len)
                    Buffer.ZeroMemory(_mem+len, pos-len); 
            }
 
            _mem[pos] = value; 
            _position = n;
        } 
    }
}

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