SafeHandle Kelas

Definisi

Ruang nama:

System.Runtime.InteropServices

Rakitan:

System.Runtime.dll

Sumber:

SafeHandle.cs

Mewakili kelas pembungkus untuk handel sistem operasi. Kelas ini harus diwariskan.

public ref class SafeHandle abstract : System::Runtime::ConstrainedExecution::CriticalFinalizerObject, IDisposable

public abstract class SafeHandle : System.Runtime.ConstrainedExecution.CriticalFinalizerObject, IDisposable

type SafeHandle = class
    inherit CriticalFinalizerObject
    interface IDisposable

Public MustInherit Class SafeHandle
Inherits CriticalFinalizerObject
Implements IDisposable

Warisan

Object

CriticalFinalizerObject

SafeHandle

Turunan

Microsoft.Win32.SafeHandles.SafeAccessTokenHandle

Microsoft.Win32.SafeHandles.SafeHandleMinusOneIsInvalid

Microsoft.Win32.SafeHandles.SafeHandleZeroOrMinusOneIsInvalid

System.Security.Cryptography.SafeEvpPKeyHandle

Penerapan

IDisposable

Contoh

Contoh kode berikut membuat handel aman kustom untuk handel file sistem operasi, yang berasal dari SafeHandleZeroOrMinusOneIsInvalid. Ini membaca byte dari file dan menampilkan nilai heksadesimalnya. Ini juga berisi harness pengujian kesalahan yang menyebabkan utas dibatalkan, tetapi nilai handel dikosongkan. Saat menggunakan IntPtr handel untuk mewakili, handel kadang-kadang bocor karena utas asinkron dibatalkan.

Anda akan memerlukan file teks di folder yang sama dengan aplikasi yang dikompilasi. Dengan asumsi bahwa Anda memberi nama aplikasi "HexViewer", penggunaan baris perintah adalah:

HexViewer <filename> -Fault

Secara opsional tentukan -Fault untuk dengan sengaja mencoba membocorkan handel dengan membatalkan utas di jendela tertentu. Gunakan alat Perfmon.exe Windows untuk memantau jumlah penanganan saat menyuntikkan kesalahan.

using System;
using System.Runtime.InteropServices;
using System.IO;
using System.ComponentModel;
using System.Security;
using System.Threading;
using Microsoft.Win32.SafeHandles;
using System.Runtime.ConstrainedExecution;
using System.Security.Permissions;

namespace SafeHandleDemo
{
    internal class MySafeFileHandle : SafeHandleZeroOrMinusOneIsInvalid
    {
        // Create a SafeHandle, informing the base class
        // that this SafeHandle instance "owns" the handle,
        // and therefore SafeHandle should call
        // our ReleaseHandle method when the SafeHandle
        // is no longer in use.
        private MySafeFileHandle()
            : base(true)
        {
        }
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        override protected bool ReleaseHandle()
        {
            // Here, we must obey all rules for constrained execution regions.
            return NativeMethods.CloseHandle(handle);
            // If ReleaseHandle failed, it can be reported via the
            // "releaseHandleFailed" managed debugging assistant (MDA).  This
            // MDA is disabled by default, but can be enabled in a debugger
            // or during testing to diagnose handle corruption problems.
            // We do not throw an exception because most code could not recover
            // from the problem.
        }
    }

    [SuppressUnmanagedCodeSecurity()]
    internal static class NativeMethods
    {
        // Win32 constants for accessing files.
        internal const int GENERIC_READ = unchecked((int)0x80000000);

        // Allocate a file object in the kernel, then return a handle to it.
        [DllImport("kernel32", SetLastError = true, CharSet = CharSet.Unicode)]
        internal extern static MySafeFileHandle CreateFile(String fileName,
           int dwDesiredAccess, System.IO.FileShare dwShareMode,
           IntPtr securityAttrs_MustBeZero, System.IO.FileMode dwCreationDisposition,
           int dwFlagsAndAttributes, IntPtr hTemplateFile_MustBeZero);

        // Use the file handle.
        [DllImport("kernel32", SetLastError = true)]
        internal extern static int ReadFile(MySafeFileHandle handle, byte[] bytes,
           int numBytesToRead, out int numBytesRead, IntPtr overlapped_MustBeZero);

        // Free the kernel's file object (close the file).
        [DllImport("kernel32", SetLastError = true)]
        [ReliabilityContract(Consistency.WillNotCorruptState, Cer.MayFail)]
        internal extern static bool CloseHandle(IntPtr handle);
    }

    // The MyFileReader class is a sample class that accesses an operating system
    // resource and implements IDisposable. This is useful to show the types of
    // transformation required to make your resource wrapping classes
    // more resilient. Note the Dispose and Finalize implementations.
    // Consider this a simulation of System.IO.FileStream.
    public class MyFileReader : IDisposable
    {
        // _handle is set to null to indicate disposal of this instance.
        private MySafeFileHandle _handle;

        public MyFileReader(String fileName)
        {
            // Security permission check.
            String fullPath = Path.GetFullPath(fileName);
            new FileIOPermission(FileIOPermissionAccess.Read, fullPath).Demand();

            // Open a file, and save its handle in _handle.
            // Note that the most optimized code turns into two processor
            // instructions: 1) a call, and 2) moving the return value into
            // the _handle field.  With SafeHandle, the CLR's platform invoke
            // marshaling layer will store the handle into the SafeHandle
            // object in an atomic fashion. There is still the problem
            // that the SafeHandle object may not be stored in _handle, but
            // the real operating system handle value has been safely stored
            // in a critical finalizable object, ensuring against leaking
            // the handle even if there is an asynchronous exception.

            MySafeFileHandle tmpHandle;
            tmpHandle = NativeMethods.CreateFile(fileName, NativeMethods.GENERIC_READ,
                FileShare.Read, IntPtr.Zero, FileMode.Open, 0, IntPtr.Zero);

            // An async exception here will cause us to run our finalizer with
            // a null _handle, but MySafeFileHandle's ReleaseHandle code will
            // be invoked to free the handle.

            // This call to Sleep, run from the fault injection code in Main,
            // will help trigger a race. But it will not cause a handle leak
            // because the handle is already stored in a SafeHandle instance.
            // Critical finalization then guarantees that freeing the handle,
            // even during an unexpected AppDomain unload.
            Thread.Sleep(500);
            _handle = tmpHandle;  // Makes _handle point to a critical finalizable object.

            // Determine if file is opened successfully.
            if (_handle.IsInvalid)
                throw new Win32Exception(Marshal.GetLastWin32Error(), fileName);
        }

        public void Dispose()  // Follow the Dispose pattern - public nonvirtual.
        {
            Dispose(disposing: true);
            GC.SuppressFinalize(this);
        }

        // No finalizer is needed. The finalizer on SafeHandle
        // will clean up the MySafeFileHandle instance,
        // if it hasn't already been disposed.
        // However, there may be a need for a subclass to
        // introduce a finalizer, so Dispose is properly implemented here.
        protected virtual void Dispose(bool disposing)
        {
            // Note there are three interesting states here:
            // 1) CreateFile failed, _handle contains an invalid handle
            // 2) We called Dispose already, _handle is closed.
            // 3) _handle is null, due to an async exception before
            //    calling CreateFile. Note that the finalizer runs
            //    if the constructor fails.
            if (_handle != null && !_handle.IsInvalid)
            {
                // Free the handle
                _handle.Dispose();
            }
            // SafeHandle records the fact that we've called Dispose.
        }

        public byte[] ReadContents(int length)
        {
            if (_handle.IsInvalid)  // Is the handle disposed?
                throw new ObjectDisposedException("FileReader is closed");

            // This sample code will not work for all files.
            byte[] bytes = new byte[length];
            int numRead = 0;
            int r = NativeMethods.ReadFile(_handle, bytes, length, out numRead, IntPtr.Zero);
            // Since we removed MyFileReader's finalizer, we no longer need to
            // call GC.KeepAlive here.  Platform invoke will keep the SafeHandle
            // instance alive for the duration of the call.
            if (r == 0)
                throw new Win32Exception(Marshal.GetLastWin32Error());
            if (numRead < length)
            {
                byte[] newBytes = new byte[numRead];
                Array.Copy(bytes, newBytes, numRead);
                bytes = newBytes;
            }
            return bytes;
        }
    }

    static class Program
    {
        // Testing harness that injects faults.
        private static bool _printToConsole = false;
        private static bool _workerStarted = false;

        private static void Usage()
        {
            Console.WriteLine("Usage:");
            // Assumes that application is named HexViewer"
            Console.WriteLine("HexViewer <fileName> [-fault]");
            Console.WriteLine(" -fault Runs hex viewer repeatedly, injecting faults.");
        }

        private static void ViewInHex(Object fileName)
        {
            _workerStarted = true;
            byte[] bytes;
            using (MyFileReader reader = new MyFileReader((String)fileName))
            {
                bytes = reader.ReadContents(20);
            }  // Using block calls Dispose() for us here.

            if (_printToConsole)
            {
                // Print up to 20 bytes.
                int printNBytes = Math.Min(20, bytes.Length);
                Console.WriteLine("First {0} bytes of {1} in hex", printNBytes, fileName);
                for (int i = 0; i < printNBytes; i++)
                    Console.Write("{0:x} ", bytes[i]);
                Console.WriteLine();
            }
        }

        static void Main(string[] args)
        {
            if (args.Length == 0 || args.Length > 2 ||
                args[0] == "-?" || args[0] == "/?")
            {
                Usage();
                return;
            }

            String fileName = args[0];
            bool injectFaultMode = args.Length > 1;
            if (!injectFaultMode)
            {
                _printToConsole = true;
                ViewInHex(fileName);
            }
            else
            {
                Console.WriteLine("Injecting faults - watch handle count in perfmon (press Ctrl-C when done)");
                int numIterations = 0;
                while (true)
                {
                    _workerStarted = false;
                    Thread t = new Thread(new ParameterizedThreadStart(ViewInHex));
                    t.Start(fileName);
                    Thread.Sleep(1);
                    while (!_workerStarted)
                    {
                        Thread.Sleep(0);
                    }
                    t.Abort();  // Normal applications should not do this.
                    numIterations++;
                    if (numIterations % 10 == 0)
                        GC.Collect();
                    if (numIterations % 10000 == 0)
                        Console.WriteLine(numIterations);
                }
            }
        }
    }
}

Keterangan

Untuk informasi selengkapnya tentang API ini, lihat Keterangan API Tambahan untuk SafeHandle.

Catatan Bagi Implementer

Untuk membuat kelas yang berasal dari SafeHandle, Anda harus tahu cara membuat dan membebaskan handel sistem operasi. Proses ini berbeda untuk jenis handel yang berbeda karena beberapa menggunakan fungsi [CloseHandle](/windows/win32/api/handleapi/nf-handleapi-closehandle), sementara yang lain menggunakan fungsi yang lebih spesifik seperti [UnmapViewOfFile](/windows/win32/api/memoryapi/nf-memoryapi-unmapviewoffile) atau [FindClose](/windows/win32/api/fileapi/nf-fileapi-findclose). Untuk alasan ini, Anda harus membuat kelas turunan SafeHandle untuk setiap jenis handel sistem operasi yang ingin Anda bungkus dalam handel yang aman.

Ketika Anda mewarisi dari SafeHandle, Anda harus mengambil alih anggota berikut: IsInvalid dan ReleaseHandle().

Anda juga harus menyediakan konstruktor tanpa parameter publik yang memanggil konstruktor dasar dengan nilai yang mewakili nilai handel yang tidak valid, dan nilai yang Boolean menunjukkan apakah handel asli dimiliki oleh SafeHandle dan akibatnya harus dibebaskan ketika telah SafeHandle dibuang.

Konstruktor

SafeHandle(IntPtr, Boolean)

Menginisialisasi instans SafeHandle baru kelas dengan nilai handel yang tidak valid yang ditentukan.

Bidang

handle

Menentukan handel yang akan dibungkus.

Properti

IsClosed	Mendapatkan nilai yang menunjukkan apakah handel ditutup.
IsInvalid	Saat ditimpa di kelas turunan, mendapatkan nilai yang menunjukkan apakah nilai handel tidak valid.

Metode

Close()	Menandai handel untuk melepaskan dan membebaskan sumber daya.
DangerousAddRef(Boolean)	Secara manual menaikkan penghitung referensi pada SafeHandle instans.
DangerousGetHandle()	Mengembalikan nilai handle bidang.
DangerousRelease()	Menurunkan penghitung referensi secara manual pada SafeHandle instans.
Dispose()	Merilis semua sumber daya yang SafeHandle digunakan oleh kelas .
Dispose(Boolean)	Merilis sumber daya tidak terkelola yang SafeHandle digunakan oleh kelas yang menentukan apakah akan melakukan operasi pembuangan normal.
Equals(Object)	Menentukan apakah objek yang ditentukan sama dengan objek saat ini. (Diperoleh dari Object)
Finalize()	Membebaskan semua sumber daya yang terkait dengan handel.
GetHashCode()	Berfungsi sebagai fungsi hash default. (Diperoleh dari Object)
GetType()	Mendapatkan instans Type saat ini. (Diperoleh dari Object)
MemberwiseClone()	Membuat salinan dangkal dari yang saat ini Object. (Diperoleh dari Object)
ReleaseHandle()	Ketika ditimpa di kelas turunan, jalankan kode yang diperlukan untuk membebaskan handel.
SetHandle(IntPtr)	Mengatur handel ke handel yang sudah ada sebelumnya yang ditentukan.
SetHandleAsInvalid()	Menandai handel sebagai tidak lagi digunakan.
ToString()	Mengembalikan string yang mewakili objek saat ini. (Diperoleh dari Object)

Lihat juga

• Microsoft.Win32.SafeHandles
• CriticalHandle
• CriticalFinalizerObject