Merge pull request #373 from mono/fix-mono-gh-16778

Fix wrong behaviour when move multiple files out of watched folder on…

6 files changed, 413 insertions, 132 deletions

diff --git a/src/Common/src/Interop/OSX/Interop.EventStream.cs b/src/Common/src/Interop/OSX/Interop.EventStream.cs
index 7c6e93c761..19e9f5cb62 100644
--- a/src/Common/src/Interop/OSX/Interop.EventStream.cs
+++ b/src/Common/src/Interop/OSX/Interop.EventStream.cs
@@ -88,10 +88,8 @@ internal static partial class Interop
             size_t numEvents,
             [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2)]
             byte** eventPaths,
-            [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2)]
-            FSEventStreamEventFlags[] eventFlags,
-            [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2)]
-            FSEventStreamEventId[] eventIds);
+            FSEventStreamEventFlags* eventFlags,
+            FSEventStreamEventId* eventIds);
 
         /// <summary>
         /// Internal wrapper to create a new EventStream to listen to events from the core OS (such as File System events).
diff --git a/src/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj b/src/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj
index c797318179..6a5fc78601 100644
--- a/src/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj
+++ b/src/System.IO.FileSystem.Watcher/src/System.IO.FileSystem.Watcher.csproj
@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="14.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003" DefaultTargets="Build">
   <Import Project="$([MSBuild]::GetDirectoryNameOfFileAbove($(MSBuildThisFileDirectory), dir.props))\dir.props" />
   <PropertyGroup>
diff --git a/src/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.OSX.cs b/src/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.OSX.cs
index 959597cfd4..1165464901 100644
--- a/src/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.OSX.cs
+++ b/src/System.IO.FileSystem.Watcher/src/System/IO/FileSystemWatcher.OSX.cs
@@ -9,10 +9,12 @@ using System.Runtime.InteropServices;
 using System.Threading;
 using System.Text;
 
+#pragma warning disable SA1121 // we don't want to simplify built-ins here as we're using aliasing
 using CFStringRef = System.IntPtr;
 using FSEventStreamRef = System.IntPtr;
 using size_t = System.IntPtr;
 using FSEventStreamEventId = System.UInt64;
+using FSEventStreamEventFlags = Interop.EventStream.FSEventStreamEventFlags;
 using CFRunLoopRef = System.IntPtr;
 using Microsoft.Win32.SafeHandles;
 
@@ -87,38 +89,38 @@ namespace System.IO
 
         private CancellationTokenSource _cancellation;
 
-        private static Interop.EventStream.FSEventStreamEventFlags TranslateFlags(NotifyFilters flagsToTranslate)
+        private static FSEventStreamEventFlags TranslateFlags(NotifyFilters flagsToTranslate)
         {
-            Interop.EventStream.FSEventStreamEventFlags flags = 0;
+            FSEventStreamEventFlags flags = 0;
 
             // Always re-create the filter flags when start is called since they could have changed
             if ((flagsToTranslate & (NotifyFilters.Attributes | NotifyFilters.CreationTime | NotifyFilters.LastAccess | NotifyFilters.LastWrite | NotifyFilters.Size)) != 0)
             {
-                flags = Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemInodeMetaMod  |
-                        Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemFinderInfoMod |
-                        Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemModified      |
-                        Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemChangeOwner;
+                flags = FSEventStreamEventFlags.kFSEventStreamEventFlagItemInodeMetaMod  |
+                        FSEventStreamEventFlags.kFSEventStreamEventFlagItemFinderInfoMod |
+                        FSEventStreamEventFlags.kFSEventStreamEventFlagItemModified      |
+                        FSEventStreamEventFlags.kFSEventStreamEventFlagItemChangeOwner;
             }
             if ((flagsToTranslate & NotifyFilters.Security) != 0)
             {
-                flags |= Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemChangeOwner |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemXattrMod;
+                flags |= FSEventStreamEventFlags.kFSEventStreamEventFlagItemChangeOwner |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemXattrMod;
             }
             if ((flagsToTranslate & NotifyFilters.DirectoryName) != 0)
             {
-                flags |= Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsDir |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsSymlink |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemCreated |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRemoved |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed;
+                flags |= FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsDir |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsSymlink |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemCreated |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemRemoved |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed;
             }
             if ((flagsToTranslate & NotifyFilters.FileName) != 0)
             {
-                flags |= Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsSymlink |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemCreated |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRemoved |
-                         Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed;
+                flags |= FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsSymlink |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemCreated |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemRemoved |
+                         FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed;
             }
 
             return flags;
@@ -127,15 +129,15 @@ namespace System.IO
         private sealed class RunningInstance
         {
             // Flags used to create the event stream
-            private const Interop.EventStream.FSEventStreamCreateFlags EventStreamFlags = (Interop.EventStream.FSEventStreamCreateFlags.kFSEventStreamCreateFlagFileEvents | 
-                                                                       Interop.EventStream.FSEventStreamCreateFlags.kFSEventStreamCreateFlagNoDefer   | 
+            private const Interop.EventStream.FSEventStreamCreateFlags EventStreamFlags = (Interop.EventStream.FSEventStreamCreateFlags.kFSEventStreamCreateFlagFileEvents |
+                                                                       Interop.EventStream.FSEventStreamCreateFlags.kFSEventStreamCreateFlagNoDefer |
                                                                        Interop.EventStream.FSEventStreamCreateFlags.kFSEventStreamCreateFlagWatchRoot);
 
             // Weak reference to the associated watcher. A weak reference is used so that the FileSystemWatcher may be collected and finalized,
             // causing an active operation to be torn down.
             private readonly WeakReference<FileSystemWatcher> _weakWatcher;
 
-            // The user can input relative paths, which can muck with our path comparisons. Save off the 
+            // The user can input relative paths, which can muck with our path comparisons. Save off the
             // actual full path so we can use it for comparing
             private string _fullDirectory;
 
@@ -143,13 +145,13 @@ namespace System.IO
             private bool _includeChildren;
 
             // The bitmask of events that we want to send to the user
-            private Interop.EventStream.FSEventStreamEventFlags _filterFlags;
+            private FSEventStreamEventFlags _filterFlags;
 
             // The EventStream to listen for events on
             private SafeEventStreamHandle _eventStream;
 
 
-            // Callback delegate for the EventStream events 
+            // Callback delegate for the EventStream events
             private Interop.EventStream.FSEventStreamCallback _callback;
 
             // Token to monitor for cancellation requests, upon which processing is stopped and all
@@ -165,7 +167,7 @@ namespace System.IO
                 FileSystemWatcher watcher,
                 string directory,
                 bool includeChildren,
-                Interop.EventStream.FSEventStreamEventFlags filter,
+                FSEventStreamEventFlags filter,
                 CancellationToken cancelToken)
             {
                 Debug.Assert(string.IsNullOrEmpty(directory) == false);
@@ -364,13 +366,9 @@ namespace System.IO
                 IntPtr clientCallBackInfo,
                 size_t numEvents,
                 byte** eventPaths,
-                [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2)]
-                Interop.EventStream.FSEventStreamEventFlags[] eventFlags,
-                [MarshalAs(UnmanagedType.LPArray, SizeParamIndex = 2)]
-                FSEventStreamEventId[] eventIds)
+                FSEventStreamEventFlags* eventFlags,
+                FSEventStreamEventId* eventIds)
             {
-                Debug.Assert((eventPaths != null) && (numEvents.ToInt32() == eventFlags.Length) && (numEvents.ToInt32() == eventIds.Length));
-
                 // Try to get the actual watcher from our weak reference.  We maintain a weak reference most of the time
                 // so as to avoid a rooted cycle that would prevent our processing loop from ever ending
                 // if the watcher is dropped by the user without being disposed. If we can't get the watcher,
@@ -386,33 +384,33 @@ namespace System.IO
                 if (context is null)
                 {
                     // Flow suppressed, just run here
-                    ProcessEvents(numEvents.ToInt32(), eventPaths, eventFlags, eventIds, watcher);
+                    ProcessEvents(numEvents.ToInt32(), eventPaths, new Span<FSEventStreamEventFlags>(eventFlags, numEvents.ToInt32()), new Span<FSEventStreamEventId>(eventIds, numEvents.ToInt32()), watcher);
                 }
                 else
                 {
                     ExecutionContext.Run(
                         context,
-                        (object o) => ((RunningInstance)o).ProcessEvents(numEvents.ToInt32(), eventPaths, eventFlags, eventIds, watcher),
+                        (object o) => ((RunningInstance)o).ProcessEvents(numEvents.ToInt32(), eventPaths, new Span<FSEventStreamEventFlags>(eventFlags, numEvents.ToInt32()), new Span<FSEventStreamEventId>(eventIds, numEvents.ToInt32()), watcher),
                         this);
                 }
             }
 
             private unsafe void ProcessEvents(int numEvents,
                 byte** eventPaths,
-                Interop.EventStream.FSEventStreamEventFlags[] eventFlags,
-                FSEventStreamEventId[] eventIds,
+                Span<FSEventStreamEventFlags> eventFlags,
+                Span<FSEventStreamEventId> eventIds,
                 FileSystemWatcher watcher)
             {
-                // Since renames come in pairs, when we find the first we need to search for the next one. Once we find it, we'll add it to this
-                // list so when the for-loop comes across it, we'll skip it since it's already been processed as part of the original of the pair.
-                List<FSEventStreamEventId> handledRenameEvents = null;
-                Memory<char>[] events = new Memory<char>[numEvents];
-                ParseEvents();
+                // Since renames come in pairs, when we reach the first we need to test for the next one if it is the case. If the next one belongs into the pair,
+                // we'll store the event id so when the for-loop comes across it, we'll skip it since it's already been processed as part of the original of the pair.
+                int? handledRenameEvents = null;
 
-                for (long i = 0; i < numEvents; i++)
+                for (int i = 0; i < numEvents; i++)
                 {
-                    ReadOnlySpan<char> path = events[i].Span;
-                    Debug.Assert(path[path.Length - 1] != '/', "Trailing slashes on events is not supported");
+                    using ParsedEvent parsedEvent = ParseEvent(eventPaths[i]);
+
+                    ReadOnlySpan<char> path = parsedEvent.Path;
+                    Debug.Assert(path[^1] != '/', "Trailing slashes on events is not supported");
 
                     // Match Windows and don't notify us about changes to the Root folder
                     if (_fullDirectory.Length >= path.Length && path.Equals(_fullDirectory.AsSpan(0, path.Length), StringComparison.OrdinalIgnoreCase))
@@ -427,7 +425,7 @@ namespace System.IO
                         watcher.OnError(new ErrorEventArgs(new IOException(SR.FSW_BufferOverflow, (int)eventFlags[i])));
                         break;
                     }
-                    else if ((handledRenameEvents != null) && (handledRenameEvents.Contains(eventIds[i])))
+                    else if (handledRenameEvents == i)
                     {
                         // If this event is the second in a rename pair then skip it
                         continue;
@@ -460,15 +458,15 @@ namespace System.IO
                         }
                         if (((eventType & WatcherChangeTypes.Renamed) > 0))
                         {
-                            // Find the rename that is paired to this rename, which should be the next rename in the list
-                            long pairedId = FindRenameChangePairedChange(i, eventFlags);
-                            if (pairedId == long.MinValue)
+                            // Find the rename that is paired to this rename.
+                            int? pairedId = FindRenameChangePairedChange(i, eventFlags, eventIds);
+                            if (!pairedId.HasValue)
                             {
-                                // Getting here means we have a rename without a pair, meaning it should be a create for the 
+                                // Getting here means we have a rename without a pair, meaning it should be a create for the
                                 // move from unwatched folder to watcher folder scenario or a move from the watcher folder out.
                                 // Check if the item exists on disk to check which it is
                                 // Don't send a new notification if we already sent one for this event.
-                                if (DoesItemExist(path, IsFlagSet(eventFlags[i], Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile)))
+                                if (DoesItemExist(path, eventFlags[i].HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile)))
                                 {
                                     if ((eventType & WatcherChangeTypes.Created) == 0)
                                     {
@@ -482,74 +480,78 @@ namespace System.IO
                             }
                             else
                             {
-                                // Remove the base directory prefix and add the paired event to the list of 
+                                // Remove the base directory prefix and add the paired event to the list of
                                 // events to skip and notify the user of the rename
-                                if (events[pairedId].Span.Length >= _fullDirectory.Length
-                                    && _fullDirectory.AsSpan().Equals(events[pairedId].Span.Slice(0, _fullDirectory.Length), StringComparison.OrdinalIgnoreCase))
-                                {
-                                    ReadOnlySpan<char> newPathRelativeName = events[pairedId].Span.Slice(_fullDirectory.Length);
-                                    watcher.NotifyRenameEventArgs(WatcherChangeTypes.Renamed, newPathRelativeName, relativePath);
-                                }
-                                else
+                                using (ParsedEvent pairedEvent = ParseEvent(eventPaths[pairedId.GetValueOrDefault()]))
                                 {
-                                    //if the base directory prefix isn't there, just use the full absolute path
-                                    watcher.NotifyRenameEventArgs(WatcherChangeTypes.Renamed, events[pairedId].Span, relativePath);
-                                }
+                                    ReadOnlySpan<char> newPathRelativeName = pairedEvent.Path;
+                                    if (newPathRelativeName.Length >= _fullDirectory.Length &&
+                                        newPathRelativeName.StartsWith(_fullDirectory, StringComparison.OrdinalIgnoreCase))
+                                    {
+                                        newPathRelativeName = newPathRelativeName.Slice(_fullDirectory.Length);
+                                    }
 
-                                // Create a new list, if necessary, and add the event
-                                if (handledRenameEvents == null)
-                                {
-                                    handledRenameEvents = new List<FSEventStreamEventId>();
+                                    watcher.NotifyRenameEventArgs(WatcherChangeTypes.Renamed, newPathRelativeName, relativePath);
                                 }
-                                handledRenameEvents.Add(eventIds[pairedId]);
+                                handledRenameEvents = pairedId.GetValueOrDefault();
                             }
                         }
                     }
-
-                    ArraySegment<char> underlyingArray;
-                    if (MemoryMarshal.TryGetArray(events[i], out underlyingArray))
-                        ArrayPool<char>.Shared.Return(underlyingArray.Array);
                 }
 
                 this._context = ExecutionContext.Capture();
 
-                void ParseEvents()
+                ParsedEvent ParseEvent(byte* nativeEventPath)
                 {
-                    for (int i = 0; i < events.Length; i++)
+                    int byteCount = 0;
+                    Debug.Assert(nativeEventPath != null);
+                    byte* temp = nativeEventPath;
+
+                    // Finds the position of null character.
+                    while (*temp != 0)
                     {
-                        int byteCount = 0;
-                        Debug.Assert(eventPaths[i] != null);
-                        byte* temp = eventPaths[i];
+                        temp++;
+                        byteCount++;
+                    }
 
-                        // Finds the position of null character.
-                        while (*temp != 0)
-                        {
-                            temp++;
-                            byteCount++;
-                        }
+                    Debug.Assert(byteCount > 0, "Empty events are not supported");
+                    char[] tempBuffer = ArrayPool<char>.Shared.Rent(Encoding.UTF8.GetMaxCharCount(byteCount));
 
-                        Debug.Assert(byteCount > 0, "Empty events are not supported");
-                        events[i] = new Memory<char>(ArrayPool<char>.Shared.Rent(Encoding.UTF8.GetMaxCharCount(byteCount)));
-                        int charCount;
+                    // Converting an array of bytes to UTF-8 char array
+                    int charCount = Encoding.UTF8.GetChars(new ReadOnlySpan<byte>(nativeEventPath, byteCount), tempBuffer);
+                    return new ParsedEvent(tempBuffer.AsSpan(0, charCount), tempBuffer);
+                }
 
-                        // Converting an array of bytes to UTF-8 char array
-                        charCount = Encoding.UTF8.GetChars(new ReadOnlySpan<byte>(eventPaths[i], byteCount), events[i].Span);
-                        events[i] = events[i].Slice(0, charCount);
-                    }
+            }
+
+            private readonly ref struct ParsedEvent
+            {
+
+                public ParsedEvent(ReadOnlySpan<char> path, char[] tempBuffer)
+                {
+                    TempBuffer = tempBuffer;
+                    Path = path;
                 }
+
+                public readonly ReadOnlySpan<char> Path;
+
+                public readonly char[] TempBuffer;
+
+                public void Dispose() => ArrayPool<char>.Shared.Return(TempBuffer);
+
             }
 
             /// <summary>
             /// Compares the given event flags to the filter flags and returns which event (if any) corresponds
             /// to those flags.
             /// </summary>
-            private WatcherChangeTypes FilterEvents(Interop.EventStream.FSEventStreamEventFlags eventFlags)
+            private WatcherChangeTypes FilterEvents(FSEventStreamEventFlags eventFlags)
             {
-                const Interop.EventStream.FSEventStreamEventFlags changedFlags = Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemInodeMetaMod |
-                                                                                 Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemFinderInfoMod |
-                                                                                 Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemModified |
-                                                                                 Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemChangeOwner |
-                                                                                 Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemXattrMod;
+                const FSEventStreamEventFlags changedFlags = FSEventStreamEventFlags.kFSEventStreamEventFlagItemInodeMetaMod |
+                                                                                 FSEventStreamEventFlags.kFSEventStreamEventFlagItemFinderInfoMod |
+                                                                                 FSEventStreamEventFlags.kFSEventStreamEventFlagItemModified |
+                                                                                 FSEventStreamEventFlags.kFSEventStreamEventFlagItemChangeOwner |
+                                                                                 FSEventStreamEventFlags.kFSEventStreamEventFlagItemXattrMod;
                 WatcherChangeTypes eventType = 0;
                 // If any of the Changed flags are set in both Filter and Event then a Changed event has occurred.
                 if (((_filterFlags & changedFlags) & (eventFlags & changedFlags)) > 0)
@@ -558,25 +560,25 @@ namespace System.IO
                 }
 
                 // Notify created/deleted/renamed events if they pass through the filters
-                bool allowDirs = (_filterFlags & Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsDir) > 0;
-                bool allowFiles = (_filterFlags & Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile) > 0;
-                bool isDir = (eventFlags & Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsDir) > 0;
-                bool isFile = (eventFlags & Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile) > 0;
+                bool allowDirs = (_filterFlags & FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsDir) > 0;
+                bool allowFiles = (_filterFlags & FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile) > 0;
+                bool isDir = (eventFlags & FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsDir) > 0;
+                bool isFile = (eventFlags & FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsFile) > 0;
                 bool eventIsCorrectType = (isDir && allowDirs) || (isFile && allowFiles);
-                bool eventIsLink = (eventFlags & (Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsHardlink | Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsSymlink | Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsLastHardlink)) > 0;
+                bool eventIsLink = (eventFlags & (FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsHardlink | FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsSymlink | FSEventStreamEventFlags.kFSEventStreamEventFlagItemIsLastHardlink)) > 0;
 
                 if (eventIsCorrectType || ((allowDirs || allowFiles) && (eventIsLink)))
                 {
                     // Notify Created/Deleted/Renamed events.
-                    if (IsFlagSet(eventFlags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed))
+                    if (eventFlags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed))
                     {
                         eventType |= WatcherChangeTypes.Renamed;
                     }
-                    if (IsFlagSet(eventFlags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemCreated))
+                    if (eventFlags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagItemCreated))
                     {
                         eventType |= WatcherChangeTypes.Created;
                     }
-                    if (IsFlagSet(eventFlags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRemoved))
+                    if (eventFlags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagItemRemoved))
                     {
                         eventType |= WatcherChangeTypes.Deleted;
                     }
@@ -584,15 +586,15 @@ namespace System.IO
                 return eventType;
             }
 
-            private bool ShouldRescanOccur(Interop.EventStream.FSEventStreamEventFlags flags)
+            private bool ShouldRescanOccur(FSEventStreamEventFlags flags)
             {
                 // Check if any bit is set that signals that the caller should rescan
-                return (IsFlagSet(flags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagMustScanSubDirs) ||
-                        IsFlagSet(flags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagUserDropped)     ||
-                        IsFlagSet(flags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagKernelDropped)   ||
-                        IsFlagSet(flags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagRootChanged)     ||
-                        IsFlagSet(flags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagMount)           ||
-                        IsFlagSet(flags, Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagUnmount));
+                return (flags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagMustScanSubDirs) ||
+                        flags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagUserDropped) ||
+                        flags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagKernelDropped) ||
+                        flags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagRootChanged) ||
+                        flags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagMount) ||
+                        flags.HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagUnmount));
             }
 
             private bool CheckIfPathIsNested(ReadOnlySpan<char> eventPath)
@@ -603,35 +605,36 @@ namespace System.IO
                 return _includeChildren || _fullDirectory.AsSpan().StartsWith(System.IO.Path.GetDirectoryName(eventPath), StringComparison.OrdinalIgnoreCase);
             }
 
-            private long FindRenameChangePairedChange(
-                long currentIndex, 
-                Interop.EventStream.FSEventStreamEventFlags[] eventFlags)
+            private unsafe int? FindRenameChangePairedChange(
+                int currentIndex,
+                Span<FSEventStreamEventFlags> flags, Span<FSEventStreamEventId> ids)
             {
-                // Start at one past the current index and try to find the next Rename item, which should be the old path.
-                for (long i = currentIndex + 1; i < eventFlags.Length; i++)
+                // The rename event can be composed of two events. The first contains the original file name the second contains the new file name.
+                // Each of the events is delivered only when the corresponding folder is watched. It means both events are delivered when the rename/move
+                // occurs inside the watched folder. When the move has origin o final destination outside, only one event is delivered. To distinguish
+                // between two nonrelated events and the event which belong together the event ID is tested. Only related rename events differ in ID by one.
+                // This behavior isn't documented and there is an open radar http://www.openradar.me/13461247.
+
+                int nextIndex = currentIndex + 1;
+
+                if (nextIndex >= flags.Length)
+                    return null;
+
+                if (ids[currentIndex] + 1 == ids[nextIndex] &&
+                    flags[nextIndex].HasFlag(FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed))
                 {
-                    if (IsFlagSet(eventFlags[i], Interop.EventStream.FSEventStreamEventFlags.kFSEventStreamEventFlagItemRenamed))
-                    {
-                        // We found match, stop looking
-                        return i;
-                    }
+                    return nextIndex;
                 }
 
-                return long.MinValue;
+                return null;
             }
-
-            private static bool IsFlagSet(Interop.EventStream.FSEventStreamEventFlags flags, Interop.EventStream.FSEventStreamEventFlags value)
-            {
-                return (value & flags) == value;
-            }
-
             private static bool DoesItemExist(ReadOnlySpan<char> path, bool isFile)
             {
                 if (path.IsEmpty || path.Length == 0)
                     return false;
 
                 if (!isFile)
-                    return  FileSystem.DirectoryExists(path);
+                    return FileSystem.DirectoryExists(path);
 #if MONO
                 return path[path.Length - 1] == '/'
 #else
diff --git a/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.Directory.Move.cs b/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.Directory.Move.cs
index 654cec1cf9..bf8da6bb14 100644
--- a/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.Directory.Move.cs
+++ b/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.Directory.Move.cs
@@ -4,6 +4,10 @@
 
 using Xunit;
 
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+
 namespace System.IO.Tests
 {
     public class Directory_Move_Tests : FileSystemWatcherTest
@@ -16,11 +20,43 @@ namespace System.IO.Tests
         }
 
         [Fact]
+        [PlatformSpecific(TestPlatforms.OSX)]
         public void Directory_Move_From_Watched_To_Unwatched()
         {
             DirectoryMove_FromWatchedToUnwatched(WatcherChangeTypes.Deleted);
         }
 
+        [Theory]
+        [PlatformSpecific(TestPlatforms.OSX)]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void Directory_Move_Multiple_From_Watched_To_Unwatched_Mac(int filesCount)
+        {
+            // On Mac, the FSStream aggregate old events caused by the test setup.
+            // There is no option how to get rid of it but skip it.
+            DirectoryMove_Multiple_FromWatchedToUnwatched(filesCount, skipOldEvents: true);
+        }
+
+        [Theory]
+        [PlatformSpecific(~TestPlatforms.OSX)]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void Directory_Move_Multiple_From_Watched_To_Unwatched(int filesCount)
+        {
+            DirectoryMove_Multiple_FromWatchedToUnwatched(filesCount, skipOldEvents: false);
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void Directory_Move_Multiple_From_Unatched_To_Watched(int filesCount)
+        {
+            DirectoryMove_Multiple_FromUnwatchedToWatched(filesCount);
+        }
+
         [Fact]
         [PlatformSpecific(TestPlatforms.Windows)]  // Expected WatcherChangeTypes are different based on OS
         public void Windows_Directory_Move_To_Different_Watched_Directory()
@@ -92,6 +128,71 @@ namespace System.IO.Tests
             }
         }
 
+        private void DirectoryMove_Multiple_FromWatchedToUnwatched(int filesCount, bool skipOldEvents)
+        {
+            Assert.InRange(filesCount, 0, int.MaxValue);
+
+            using var watchedTestDirectory = new TempDirectory(GetTestFilePath());
+            using var unwatchedTestDirectory = new TempDirectory(GetTestFilePath());
+
+            var dirs = Enumerable.Range(0, filesCount)
+                            .Select(i => new
+                            {
+                                DirecoryInWatchedDir = Path.Combine(watchedTestDirectory.Path, $"dir{i}"),
+                                DirecoryInUnwatchedDir = Path.Combine(unwatchedTestDirectory.Path, $"dir{i}")
+                            }).ToArray();
+
+            Array.ForEach(dirs, (dir) => Directory.CreateDirectory(dir.DirecoryInWatchedDir));
+
+            using var watcher = new FileSystemWatcher(watchedTestDirectory.Path, "*");
+
+            Action action = () => Array.ForEach(dirs, dir => Directory.Move(dir.DirecoryInWatchedDir, dir.DirecoryInUnwatchedDir));
+
+            // On macOS, for each file we receive two events as describe in comment below.
+            int expectEvents = filesCount;
+            if (skipOldEvents)
+                expectEvents = expectEvents * 2;
+
+            IEnumerable<FiredEvent> events = ExpectEvents(watcher, expectEvents, action);
+
+            if (skipOldEvents)
+                events = events.Where(x => x.EventType != WatcherChangeTypes.Created);
+
+            var expectedEvents = dirs.Select(dir => new FiredEvent(WatcherChangeTypes.Deleted, dir.DirecoryInWatchedDir));
+
+            // Remove Created events as there is racecondition when create dir and then observe parent folder. It receives Create event altought Watcher is not registered yet.
+            Assert.Equal(expectedEvents, events.Where(x => x.EventType != WatcherChangeTypes.Created));
+
+
+        }
+
+        private void DirectoryMove_Multiple_FromUnwatchedToWatched(int filesCount)
+        {
+            Assert.InRange(filesCount, 0, int.MaxValue);
+
+            using var watchedTestDirectory = new TempDirectory(GetTestFilePath());
+            using var unwatchedTestDirectory = new TempDirectory(GetTestFilePath());
+
+
+            var dirs = Enumerable.Range(0, filesCount)
+                            .Select(i => new
+                            {
+                                DirecoryInWatchedDir = Path.Combine(watchedTestDirectory.Path, $"dir{i}"),
+                                DirecoryInUnwatchedDir = Path.Combine(unwatchedTestDirectory.Path, $"dir{i}")
+                            }).ToArray();
+
+            Array.ForEach(dirs, (dir) => Directory.CreateDirectory(dir.DirecoryInUnwatchedDir));
+
+            using var watcher = new FileSystemWatcher(watchedTestDirectory.Path, "*");
+
+            Action action = () => Array.ForEach(dirs, dir => Directory.Move(dir.DirecoryInUnwatchedDir, dir.DirecoryInWatchedDir));
+
+            List<FiredEvent> events = ExpectEvents(watcher, filesCount, action);
+            var expectedEvents = dirs.Select(dir => new FiredEvent(WatcherChangeTypes.Created, dir.DirecoryInWatchedDir));
+
+            Assert.Equal(expectedEvents, events);
+        }
+
         private void DirectoryMove_FromWatchedToUnwatched(WatcherChangeTypes eventType)
         {
             using (var watchedTestDirectory = new TempDirectory(GetTestFilePath()))
@@ -168,4 +269,4 @@ namespace System.IO.Tests
 
         #endregion
     }
-}
\ No newline at end of file
+}
diff --git a/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.File.Move.cs b/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.File.Move.cs
index f9e37eeb2d..be9d25490f 100644
--- a/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.File.Move.cs
+++ b/src/System.IO.FileSystem.Watcher/tests/FileSystemWatcher.File.Move.cs
@@ -2,6 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
 using Xunit;
 
 namespace System.IO.Tests
@@ -28,6 +31,37 @@ namespace System.IO.Tests
             FileMove_FromWatchedToUnwatched(WatcherChangeTypes.Deleted);
         }
 
+        [Theory]
+        [PlatformSpecific(TestPlatforms.OSX)]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void File_Move_Multiple_From_Watched_To_Unwatched_Mac(int filesCount)
+        {
+            // On Mac, the FSStream aggregate old events caused by the test setup.
+            // There is no option how to get rid of it but skip it.
+            FileMove_Multiple_FromWatchedToUnwatched(filesCount, skipOldEvents: true);
+        }
+
+        [Theory]
+        [PlatformSpecific(~TestPlatforms.OSX)]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void File_Move_From_Watched_To_Unwatched(int filesCount)
+        {
+            FileMove_Multiple_FromWatchedToUnwatched(filesCount, skipOldEvents: false);
+        }
+
+        [Theory]
+        [InlineData(1)]
+        [InlineData(2)]
+        [InlineData(3)]
+        public void File_Move_Multiple_From_Unwatched_To_WatchedMac(int filesCount)
+        {
+            FileMove_Multiple_FromUnwatchedToWatched(filesCount);
+        }
+
         [Fact]
         [PlatformSpecific(TestPlatforms.Windows)]  // Expected WatcherChangeTypes are different based on OS
         public void Windows_File_Move_To_Different_Watched_Directory()
@@ -147,6 +181,74 @@ namespace System.IO.Tests
             }
         }
 
+        private void FileMove_Multiple_FromWatchedToUnwatched(int filesCount, bool skipOldEvents)
+        {
+            Assert.InRange(filesCount, 0, int.MaxValue);
+
+            using var testDirectory = new TempDirectory(GetTestFilePath());
+            using var watchedTestDirectory = new TempDirectory(Path.Combine(testDirectory.Path, "dir_watched"));
+            using var unwatchedTestDirectory = new TempDirectory(Path.Combine(testDirectory.Path, "dir_unwatched"));
+
+            var files = Enumerable.Range(0, filesCount)
+                            .Select(i => new
+                            {
+                                FileInWatchedDir = Path.Combine(watchedTestDirectory.Path, $"file{i}"),
+                                FileInUnwatchedDir = Path.Combine(unwatchedTestDirectory.Path, $"file{i}")
+                            }).ToArray();
+
+            Array.ForEach(files, (file) => File.Create(file.FileInWatchedDir).Dispose());
+
+            using var watcher = new FileSystemWatcher(watchedTestDirectory.Path, "*");
+
+            Action action = () => Array.ForEach(files, file => File.Move(file.FileInWatchedDir, file.FileInUnwatchedDir));
+
+            // On macOS, for each file we receive two events as describe in comment below.
+            int expectEvents = filesCount;
+            if (skipOldEvents)
+            {
+                expectEvents = expectEvents * 3;
+            }
+
+            IEnumerable<FiredEvent> events = ExpectEvents(watcher, expectEvents, action);
+
+            // Remove Created and Changed events as there is racecondition when create file and then observe parent folder. It receives Create and Changed event altought Watcher is not registered yet.
+            if (skipOldEvents)
+            {
+                events = events.Where(x => (x.EventType & (WatcherChangeTypes.Created | WatcherChangeTypes.Changed)) == 0);
+            }
+
+            var expectedEvents = files.Select(file => new FiredEvent(WatcherChangeTypes.Deleted, file.FileInWatchedDir));
+
+            Assert.Equal(expectedEvents, events);
+        }
+
+        private void FileMove_Multiple_FromUnwatchedToWatched(int filesCount)
+        {
+            Assert.InRange(filesCount, 0, int.MaxValue);
+
+            using var testDirectory = new TempDirectory(GetTestFilePath());
+            using var watchedTestDirectory = new TempDirectory(Path.Combine(testDirectory.Path, "dir_watched"));
+            using var unwatchedTestDirectory = new TempDirectory(Path.Combine(testDirectory.Path, "dir_unwatched"));
+
+            var files = Enumerable.Range(0, filesCount)
+                            .Select(i => new
+                            {
+                                FileInWatchedDir = Path.Combine(watchedTestDirectory.Path, $"file{i}"),
+                                FileInUnwatchedDir = Path.Combine(unwatchedTestDirectory.Path, $"file{i}")
+                            }).ToArray();
+
+            Array.ForEach(files, (file) => File.Create(file.FileInUnwatchedDir).Dispose());
+
+            using var watcher = new FileSystemWatcher(watchedTestDirectory.Path, "*");
+
+            Action action = () => Array.ForEach(files, file => File.Move(file.FileInUnwatchedDir, file.FileInWatchedDir));
+
+            List<FiredEvent> events = ExpectEvents(watcher, filesCount, action);
+            var expectedEvents = files.Select(file => new FiredEvent(WatcherChangeTypes.Created, file.FileInWatchedDir));
+
+            Assert.Equal(expectedEvents, events);
+        }
+
         private void FileMove_FromUnwatchedToWatched(WatcherChangeTypes eventType)
         {
             using (var testDirectory = new TempDirectory(GetTestFilePath()))
@@ -213,4 +315,4 @@ namespace System.IO.Tests
 
         #endregion
     }
-}
\ No newline at end of file
+}
diff --git a/src/System.IO.FileSystem.Watcher/tests/Utility/FileSystemWatcherTest.cs b/src/System.IO.FileSystem.Watcher/tests/Utility/FileSystemWatcherTest.cs
index 0ce6ebb12b..78dccce319 100644
--- a/src/System.IO.FileSystem.Watcher/tests/Utility/FileSystemWatcherTest.cs
+++ b/src/System.IO.FileSystem.Watcher/tests/Utility/FileSystemWatcherTest.cs
@@ -484,5 +484,82 @@ namespace System.IO.Tests
             return newWatcher;
         }
 #endif
+
+        internal readonly struct FiredEvent
+        {
+            public FiredEvent(WatcherChangeTypes eventType, string dir1, string dir2 = "") => (EventType, Dir1, Dir2) = (eventType, dir1, dir2);
+
+            public readonly WatcherChangeTypes EventType;
+            public readonly string Dir1;
+            public readonly string Dir2;
+
+            public override bool Equals(object obj) => obj is FiredEvent evt && Equals(evt);
+
+            public bool Equals(FiredEvent other) => EventType == other.EventType &&
+                Dir1 == other.Dir1 &&
+                Dir2 == other.Dir2;
+
+
+            public override int GetHashCode() => EventType.GetHashCode() ^ Dir1.GetHashCode() ^ Dir2.GetHashCode();
+
+            public override string ToString() => $"{EventType} {Dir1} {Dir2}";
+
+        }
+
+        // Observe until an expected count of events is triggered, otherwise fail. Return all collected events.
+        internal static List<FiredEvent> ExpectEvents(FileSystemWatcher watcher, int expectedEvents, Action action)
+        {
+            using var eventsOccured = new AutoResetEvent(false);
+            var eventsOrrures = 0;
+
+            var events = new List<FiredEvent>();
+
+            ErrorEventArgs error = null;
+
+            FileSystemEventHandler fileWatcherEvent = (_, e) => AddEvent(e.ChangeType, e.FullPath);
+            RenamedEventHandler renameWatcherEvent = (_, e) => AddEvent(e.ChangeType, e.FullPath, e.OldFullPath);
+            ErrorEventHandler errorHandler = (_, e) => error ??= e ?? new ErrorEventArgs(null);
+
+            watcher.Changed += fileWatcherEvent;
+            watcher.Created += fileWatcherEvent;
+            watcher.Deleted += fileWatcherEvent;
+            watcher.Renamed += renameWatcherEvent;
+            watcher.Error += errorHandler;
+
+            bool raisingEvent = watcher.EnableRaisingEvents;
+            watcher.EnableRaisingEvents = true;
+
+            try
+            {
+                action();
+                eventsOccured.WaitOne(new TimeSpan(0, 0, 5));
+            }
+            finally
+            {
+                watcher.Changed -= fileWatcherEvent;
+                watcher.Created -= fileWatcherEvent;
+                watcher.Deleted -= fileWatcherEvent;
+                watcher.Renamed -= renameWatcherEvent;
+                watcher.Error -= errorHandler;
+                watcher.EnableRaisingEvents = raisingEvent;
+            }
+
+            if (error != null)
+            {
+                Assert.False(true, $"Filewatcher error event triggered: { error.GetException()?.Message ?? "Unknow error" }");
+            }
+            Assert.True(eventsOrrures == expectedEvents, $"Expected events ({expectedEvents}) count doesn't match triggered events count ({eventsOrrures}):{Environment.NewLine}{String.Join(Environment.NewLine, events)}");
+
+            return events;
+
+            void AddEvent(WatcherChangeTypes eventType, string dir1, string dir2 = "")
+            {
+                events.Add(new FiredEvent(eventType, dir1, dir2));
+                if (Interlocked.Increment(ref eventsOrrures) == expectedEvents)
+                {
+                    eventsOccured.Set();
+                }
+            }
+        }
     }
 }
\ No newline at end of file