Long live QLockFile

Locking between processes, implemented with open(O_EXCL) on Unix
and CreateFile(CREATE_NEW) on Windows.

Supports detecting stale lock files and deleting them.
Advisory locking is used to prevent deletion of files that are still in use.

Change-Id: Id00ee2a4e77a29483d869037c7047c59cb909339
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 138 insertions, 0 deletions

diff --git a/src/corelib/io/qlockfile_win.cpp b/src/corelib/io/qlockfile_win.cpp
new file mode 100644
index 0000000000..b5f6d9f3da
--- /dev/null
+++ b/src/corelib/io/qlockfile_win.cpp
@@ -0,0 +1,138 @@
+/****************************************************************************
+**
+** Copyright (C) 2013 David Faure <faure+bluesystems@kde.org>
+** Contact: http://www.qt-project.org/legal
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and Digia.  For licensing terms and
+** conditions see http://qt.digia.com/licensing.  For further information
+** use the contact form at http://qt.digia.com/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Digia gives you certain additional
+** rights.  These rights are described in the Digia Qt LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "private/qlockfile_p.h"
+#include "private/qfilesystementry_p.h"
+#include <qt_windows.h>
+
+#include "QtCore/qcoreapplication.h"
+#include "QtCore/qfileinfo.h"
+#include "QtCore/qdatetime.h"
+#include "QtCore/qdebug.h"
+
+QT_BEGIN_NAMESPACE
+
+QLockFile::LockError QLockFilePrivate::tryLock_sys()
+{
+    SECURITY_ATTRIBUTES securityAtts = { sizeof(SECURITY_ATTRIBUTES), NULL, FALSE };
+    const QFileSystemEntry fileEntry(fileName);
+    // When writing, allow others to read.
+    // When reading, QFile will allow others to read and write, all good.
+    // Adding FILE_SHARE_DELETE would allow forceful deletion of stale files,
+    // but Windows doesn't allow recreating it while this handle is open anyway,
+    // so this would only create confusion (can't lock, but no lock file to read from).
+    const DWORD dwShareMode = FILE_SHARE_READ;
+    HANDLE fh = CreateFile((const wchar_t*)fileEntry.nativeFilePath().utf16(),
+                           GENERIC_WRITE,
+                           dwShareMode,
+                           &securityAtts,
+                           CREATE_NEW, // error if already exists
+                           FILE_ATTRIBUTE_NORMAL,
+                           NULL);
+    if (fh == INVALID_HANDLE_VALUE) {
+        const DWORD lastError = GetLastError();
+        switch (lastError) {
+        case ERROR_SHARING_VIOLATION:
+        case ERROR_ALREADY_EXISTS:
+        case ERROR_FILE_EXISTS:
+        case ERROR_ACCESS_DENIED: // readonly file, or file still in use by another process. Assume the latter, since we don't create it readonly.
+            return QLockFile::LockFailedError;
+        default:
+            qWarning() << "Got unexpected locking error" << lastError;
+            return QLockFile::UnknownError;
+        }
+    }
+
+    // We hold the lock, continue.
+    fileHandle = fh;
+    // Assemble data, to write in a single call to write
+    // (otherwise we'd have to check every write call)
+    QByteArray fileData;
+    fileData += QByteArray::number(QCoreApplication::applicationPid());
+    fileData += '\n';
+    fileData += qAppName().toUtf8();
+    fileData += '\n';
+    //fileData += localHostname(); // gethostname requires winsock init, see QHostInfo...
+    fileData += '\n';
+    DWORD bytesWritten = 0;
+    QLockFile::LockError error = QLockFile::NoError;
+    if (!WriteFile(fh, fileData.constData(), fileData.size(), &bytesWritten, NULL) || !FlushFileBuffers(fh))
+        error = QLockFile::UnknownError; // partition full
+    return error;
+}
+
+bool QLockFilePrivate::removeStaleLock()
+{
+    // QFile::remove fails on Windows if the other process is still using the file, so it's not stale.
+    return QFile::remove(fileName);
+}
+
+bool QLockFilePrivate::isApparentlyStale() const
+{
+    qint64 pid;
+    QString hostname, appname;
+    if (!getLockInfo(&pid, &hostname, &appname))
+        return false;
+
+    HANDLE procHandle = ::OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pid);
+    if (!procHandle)
+        return true;
+    // We got a handle but check if process is still alive
+    DWORD dwR = ::WaitForSingleObject(procHandle, 0);
+    ::CloseHandle(procHandle);
+    if (dwR == WAIT_TIMEOUT)
+        return true;
+    const qint64 age = QFileInfo(fileName).lastModified().msecsTo(QDateTime::currentDateTime());
+    return staleLockTime > 0 && age > staleLockTime;
+}
+
+void QLockFile::unlock()
+{
+    Q_D(QLockFile);
+     if (!d->isLocked)
+        return;
+     CloseHandle(d->fileHandle);
+     QFile::remove(d->fileName);
+     d->lockError = QLockFile::NoError;
+     d->isLocked = false;
+}
+
+QT_END_NAMESPACE