Отправка экземпляра Callback в качестве указателя на функцию приводит к тому, что «this» становится «нулевым» в C # - PullRequest
1 голос
/ 22 марта 2012

Я работаю над написанием FileSystemWatcher с использованием Mono, но по какой-то причине обратный вызов, который я отправляю в библиотеку FSEvents, не поддерживает ссылку this , она всегда пуста внутри обратный вызов, даже если обратный вызов является методом экземпляра.

Есть идеи, почему это происходит?

    using System;
    using System.IO;
    using System.Collections.Generic;
    using System.Runtime.InteropServices;
    using MonoMac.Foundation;
    using System.Threading;
    using NUnit.Framework;
    using System.Text;

    namespace Test
    {
        class MainClass
        {
            public void Main ()
            {
                string testFolder = Path.Combine (Environment.GetFolderPath (Environment.SpecialFolder.MyDocuments), "mono-test");

                if (Directory.Exists (testFolder)) {
                    Directory.Delete (testFolder, true);
                }
                Directory.CreateDirectory (testFolder);

                IntPtr path = CFStringCreateWithCString (IntPtr.Zero, testFolder, 0);
                IntPtr paths = CFArrayCreate (IntPtr.Zero, new IntPtr [1] { path }, 1, IntPtr.Zero);

                IntPtr stream = FSEventStreamCreate (IntPtr.Zero, this.Callback, IntPtr.Zero, paths, FSEventStreamEventIdSinceNow, 0, FSEventStreamCreateFlags.WatchRoot | FSEventStreamCreateFlags.FileEvents);

                CFRelease (paths);
                CFRelease (path);

                Thread runLoop = new Thread (delegate() {
                    FSEventStreamScheduleWithRunLoop (stream, CFRunLoopGetCurrent (), kCFRunLoopDefaultMode);
                    FSEventStreamStart (stream);
                    CFRunLoopRun ();
                });
                runLoop.Name = "FSEventStream";
                runLoop.Start ();

                Thread.Sleep (3000);

                string file1 = Path.Combine (testFolder, "file1.txt");
                //Thread.Sleep(1000);
                using (System.IO.File.Create(file1)) {
                }
                //Thread.Sleep(1000);
                System.IO.File.WriteAllText (file1, "file1");
                //Thread.Sleep(1000);
                System.IO.File.Delete (file1);          

            }

            public static void Main (string[] args)
            {
                new MainClass().Main();
            }

            private static IDictionary<IntPtr, MainClass> thisDict = new Dictionary<IntPtr, MainClass>();

            private void Callback (IntPtr streamRef, IntPtr clientCallBackInfo, int numEvents, IntPtr eventPaths, IntPtr eventFlags, IntPtr eventIds)
            {
                MainClass thisObj;
                if (this != null) {
                    thisDict.Add(streamRef, this);
                    thisObj = this;
                } else {
                    thisObj = thisDict[streamRef];
                }
                Console.WriteLine("\n{0}", this != null ? "this is not null" : "this is null");
                Console.WriteLine("{0}\n", thisObj != null ? "thisObj is not null" : "thisObj is null");

                string[] paths = new string[numEvents];
                UInt32[] flags = new UInt32[numEvents];
                UInt64[] ids = new UInt64[numEvents];
                unsafe
                {
                    char** eventPathsPointer = (char**) eventPaths.ToPointer();
                    uint* eventFlagsPointer = (uint*) eventFlags.ToPointer();
                    ulong* eventIdsPointer = (ulong*) eventIds.ToPointer();
                    for (int i = 0; i < numEvents; i++)
                    {
                        paths[i] = Marshal.PtrToStringAuto(new IntPtr(eventPathsPointer[i]));
                        flags[i] = eventFlagsPointer[i];
                        ids[i] = eventIdsPointer[i];
                    }
                }
                Console.WriteLine("Number of events: {0}", numEvents);
                for (int i = 0; i < numEvents; i++)
                {
                    Console.WriteLine("{0} {1:x8} {2}", ids[i], flags[i], paths[i]);
                    Console.WriteLine("Modified: {0:x8}", (flags[i] & (uint) FSEventStreamEventFlagItem.Modified));
                    Console.WriteLine("Created:  {0:x8}", (flags[i] & (uint) FSEventStreamEventFlagItem.Created));
                    Console.WriteLine("Removed:  {0:x8}", (flags[i] & (uint) FSEventStreamEventFlagItem.Removed));
                    Console.WriteLine("Renamed:  {0:x8}", (flags[i] & (uint) FSEventStreamEventFlagItem.Renamed));
                    Console.WriteLine();
                }
            }

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static IntPtr CFStringCreateWithCString (IntPtr allocator, string value, int encoding);

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static IntPtr CFArrayCreate (IntPtr allocator, IntPtr [] values, int numValues, IntPtr callBacks);

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static IntPtr CFArrayGetValueAtIndex(IntPtr array, int index);

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static void CFRelease(IntPtr cf);

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static IntPtr CFRunLoopGetCurrent ();

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static IntPtr CFRunLoopGetMain();

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static void CFRunLoopRun ();

            [DllImport ("/System/Library/Frameworks/CoreFoundation.framework/CoreFoundation")]
            extern static int CFRunLoopRunInMode (IntPtr mode, double seconds, int returnAfterSourceHandled);

            delegate void FSEventStreamCallback (IntPtr streamRef, IntPtr clientCallBackInfo, int numEvents, IntPtr eventPaths, IntPtr eventFlags, IntPtr eventIds);

            [DllImport ("/System/Library/Frameworks/CoreServices.framework/CoreServices")]
            extern static IntPtr FSEventStreamCreate (IntPtr allocator, FSEventStreamCallback callback, IntPtr context, IntPtr pathsToWatch, ulong sinceWhen, double latency, FSEventStreamCreateFlags flags);

            [DllImport ("/System/Library/Frameworks/CoreServices.framework/CoreServices")]
            extern static int FSEventStreamStart (IntPtr streamRef);

            [DllImport ("/System/Library/Frameworks/CoreServices.framework/CoreServices")]
            extern static void FSEventStreamStop (IntPtr streamRef);

            [DllImport ("/System/Library/Frameworks/CoreServices.framework/CoreServices")]
            extern static void FSEventStreamRelease (IntPtr streamRef);

            [DllImport ("/System/Library/Frameworks/CoreServices.framework/CoreServices")]
            extern static void FSEventStreamScheduleWithRunLoop (IntPtr streamRef, IntPtr runLoop, IntPtr runLoopMode);

            [DllImport ("/System/Library/Frameworks/CoreServices.framework/CoreServices")]
            extern static void FSEventStreamUnscheduleFromRunLoop (IntPtr streamRef, IntPtr runLoop, IntPtr runLoopMode);

            const ulong FSEventStreamEventIdSinceNow = ulong.MaxValue;

            private static IntPtr kCFRunLoopDefaultMode = CFStringCreateWithCString(IntPtr.Zero, "kCFRunLoopDefaultMode", 0);

            [Flags()]
            enum FSEventStreamCreateFlags : uint {
                None = 0x00000000,
                UseCFTypes = 0x00000001,
                NoDefer = 0x00000002,
                WatchRoot = 0x00000004,
                IgnoreSelf = 0x00000008,
                FileEvents = 0x00000010
            }

            [Flags()]
            enum FSEventStreamEventFlag : uint {
                None = 0x00000000,
                MustScanSubDirs = 0x00000001,
                UserDropped = 0x00000002,
                KernelDropped = 0x00000004,
                EventIdsWrapped = 0x00000008,
                HistoryDone = 0x00000010,
                RootChanged = 0x00000020,
                FlagMount  = 0x00000040,
                Unmount = 0x00000080
            }

            [Flags()]
            enum FSEventStreamEventFlagItem : uint {
                Created       = 0x00000100,
                Removed       = 0x00000200,
                InodeMetaMod  = 0x00000400,
                Renamed       = 0x00000800,
                Modified      = 0x00001000,
                FinderInfoMod = 0x00002000,
                ChangeOwner   = 0x00004000,
                XattrMod      = 0x00008000,
                IsFile        = 0x00010000,
                IsDir         = 0x00020000,
                IsSymlink     = 0x00040000
            }
        }
    }

UPDATE

Фиксированный код здесь для всех, кто заинтересован.

1 Ответ

2 голосов
/ 23 марта 2012

Когда вы передаете делегат нативному методу, среда выполнения не может узнать, как долго нативный метод будет удерживать указатель на функцию, поэтому вы должны сохранить делегат живым.Если вы не сохраните ссылку на него, сборщик мусора может собрать делегат, что приведет к неопределенному поведению, когда нативный код попытается вызвать его.

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