Windows filewatcher: switch to ReadDirectoryChangesW.

Based on danimo's #2454 fix for #2455 and related to #2297.

2 files changed, 104 insertions, 30 deletions

diff --git a/src/mirall/folderwatcher_win.cpp b/src/mirall/folderwatcher_win.cpp
index c6c8242fa..ced1c2d23 100644
--- a/src/mirall/folderwatcher_win.cpp
+++ b/src/mirall/folderwatcher_win.cpp
@@ -13,6 +13,7 @@
 
 #include <QThread>
 #include <QDebug>
+#include <QDir>
 
 #include "mirall/folderwatcher.h"
 #include "mirall/folderwatcher_win.h"
@@ -23,52 +24,123 @@
 
 namespace Mirall {
 
-void WatcherThread::run()
+void WatcherThread::watchChanges(size_t fileNotifyBufferSize,
+                                 bool* increaseBufferSize)
 {
-    _handle = FindFirstChangeNotification((wchar_t*)_path.utf16(),
-                                         true, // recursive watch
-                                         FILE_NOTIFY_CHANGE_FILE_NAME |
-                                         FILE_NOTIFY_CHANGE_DIR_NAME |
-                                         FILE_NOTIFY_CHANGE_LAST_WRITE);
+    *increaseBufferSize = false;
+
+    _handle = CreateFileW(
+        (wchar_t*)_path.utf16(),
+        FILE_LIST_DIRECTORY,
+        FILE_SHARE_WRITE | FILE_SHARE_READ | FILE_SHARE_DELETE,
+        NULL,
+        OPEN_EXISTING,
+        FILE_FLAG_BACKUP_SEMANTICS,
+        NULL
+        );
 
     if (_handle == INVALID_HANDLE_VALUE)
     {
-        qDebug() << Q_FUNC_INFO << "FindFirstChangeNotification function failed, stopping watcher!";
-        FindCloseChangeNotification(_handle);
+        DWORD errorCode = GetLastError();
+        qDebug() << Q_FUNC_INFO << "Failed to create handle for" << _path << ", error:" << errorCode;
         _handle = 0;
         return;
     }
 
-    if (_handle == NULL)
-    {
-        qDebug() << Q_FUNC_INFO << "FindFirstChangeNotification returned null, stopping watcher!";
-        FindCloseChangeNotification(_handle);
-        _handle = 0;
-        return;
-    }
+    // QVarLengthArray ensures the stack-buffer is aligned like double and qint64.
+    QVarLengthArray<char, 4096*10> fileNotifyBuffer;
+    fileNotifyBuffer.resize(fileNotifyBufferSize);
+
+    const size_t fileNameBufferSize = 4096;
+    TCHAR fileNameBuffer[fileNameBufferSize];
+
+    forever {
+        FILE_NOTIFY_INFORMATION *pFileNotifyBuffer =
+                (FILE_NOTIFY_INFORMATION*)fileNotifyBuffer.data();
+        DWORD dwBytesReturned = 0;
+        SecureZeroMemory(pFileNotifyBuffer, fileNotifyBufferSize);
+        if(ReadDirectoryChangesW( _handle, (LPVOID)pFileNotifyBuffer,
+                                  fileNotifyBufferSize, true,
+                                  FILE_NOTIFY_CHANGE_FILE_NAME |
+                                  FILE_NOTIFY_CHANGE_DIR_NAME |
+                                  FILE_NOTIFY_CHANGE_LAST_WRITE,
+                                  &dwBytesReturned, NULL, NULL))
+        {
+            FILE_NOTIFY_INFORMATION *curEntry = pFileNotifyBuffer;
+            forever {
+                size_t len = curEntry->FileNameLength / 2;
+                QString file = _path + "\\" + QString::fromWCharArray(curEntry->FileName, len);
+
+                // Unless the file was removed or renamed, get its full long name
+                // TODO: We could still try expanding the path in the tricky cases...
+                QString longfile = file;
+                if (curEntry->Action != FILE_ACTION_REMOVED
+                        && curEntry->Action != FILE_ACTION_RENAMED_OLD_NAME) {
+                    size_t longNameSize = GetLongPathNameW(reinterpret_cast<LPCWSTR>(file.utf16()), fileNameBuffer, fileNameBufferSize);
+                    if (longNameSize > 0) {
+                        longfile = QString::fromUtf16(reinterpret_cast<const ushort *>(fileNameBuffer), longNameSize);
+                    } else {
+                        qDebug() << Q_FUNC_INFO << "Error converting file name to full length, keeping original name.";
+                    }
+                }
+                longfile = QDir::cleanPath(longfile);
+
+                qDebug() << Q_FUNC_INFO << "Found change in" << longfile << "action:" << curEntry->Action;
+                emit changed(longfile);
 
-    while(true) {
-        switch(WaitForSingleObject(_handle, /*wait*/ INFINITE)) {
-        case WAIT_OBJECT_0:
-            if (FindNextChangeNotification(_handle) == false) {
-                qDebug() << Q_FUNC_INFO << "FindFirstChangeNotification returned FALSE, stopping watcher!";
-                FindCloseChangeNotification(_handle);
-                _handle = 0;
-                return;
+                if (curEntry->NextEntryOffset == 0) {
+                    break;
+                }
+                curEntry = (FILE_NOTIFY_INFORMATION*)(
+                                (char*)curEntry + curEntry->NextEntryOffset);
             }
-            // qDebug() << Q_FUNC_INFO << "Change detected in" << _path << "from" << QThread::currentThread    ();
-            emit changed(_path);
-            break;
-        default:
-            qDebug()  << Q_FUNC_INFO << "Error while watching";
+        } else {
+            DWORD errorCode = GetLastError();
+            switch(errorCode) {
+            case ERROR_NOTIFY_ENUM_DIR:
+                qDebug() << Q_FUNC_INFO << "The buffer for changes overflowed! Triggering a generic change and resizing";
+                emit changed(_path);
+                *increaseBufferSize = true;
+                break;
+            default:
+                qDebug() << Q_FUNC_INFO << "General error" << errorCode << "while watching. Exiting.";
+                break;
+            }
+            CloseHandle(_handle);
+            _handle = NULL;
+            return;
+        }
+    }
+}
+
+void WatcherThread::run()
+{
+    // If this buffer fills up before we've extracted its data we will lose
+    // change information. Therefore start big.
+    size_t bufferSize = 4096*10;
+    size_t maxBuffer = 64*1024;
+
+    forever {
+        bool increaseBufferSize = false;
+        watchChanges(bufferSize, &increaseBufferSize);
+
+        if (increaseBufferSize) {
+            bufferSize = qMin(bufferSize*2, maxBuffer);
+        } else {
+            // Other errors shouldn't actually happen,
+            // so sleep a bit to avoid running into the same error case in a
+            // tight loop.
+            sleep(2);
         }
     }
 }
 
 WatcherThread::~WatcherThread()
 {
-    if (_handle)
-        FindCloseChangeNotification(_handle);
+    if (_handle) {
+        CloseHandle(_handle);
+        _handle = NULL;
+    }
 }
 
 FolderWatcherPrivate::FolderWatcherPrivate(FolderWatcher *p, const QString& path)
diff --git a/src/mirall/folderwatcher_win.h b/src/mirall/folderwatcher_win.h
index 56ddfccd0..465477fd9 100644
--- a/src/mirall/folderwatcher_win.h
+++ b/src/mirall/folderwatcher_win.h
@@ -33,6 +33,8 @@ public:
 
 protected:
     void run();
+    void watchChanges(size_t fileNotifyBufferSize,
+                      bool* increaseBufferSize);
 
 signals:
     void changed(const QString &path);