Mumble: implement lock file mechanism for Windows.

The RPC/DBus-based method for ensuring that only a single instance of
Mumble is running is racy.

If one of the processes has started it's RPC listener, it works fine.
But if both processes are started at almost the same time, it's very
likely that neither process has started listening for RPC. And the
exclusivity check fails.

In order to be completely sure that only a single Mumble instance is
running, we now take a lock file.

The lock file logic is implemented in a new class, UserLockFile.

We open a lock file file in the data directory (for Windows, that's
%APPDATA%\Mumble). The file has sharing disabled, so as long as the
process that created the file is running, no other process can access
it.

If a second instance of Mumble is launched, and the file is inaccessible,
that instance terminates itself.

It is, of course, still possible to override the single instance
limitation by passing the '-m' flag to Mumble.

Fixes #1797

src/mumble/UserLockFile.h

@@ -0,0 +1,71 @@
+/* Copyright (C) 2015, Mikkel Krautz <mikkel@krautz.dk>
+
+   All rights reserved.
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions
+   are met:
+
+   - Redistributions of source code must retain the above copyright notice,
+     this list of conditions and the following disclaimer.
+   - Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+   - Neither the name of the Mumble Developers nor the names of its
+     contributors may be used to endorse or promote products derived from this
+     software without specific prior written permission.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR
+   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#ifndef MUMBLE_MUMBLE_LOCKFILE_H_
+#define MUMBLE_MUMBLE_LOCKFILE_H_
+
+#if defined(Q_OS_WIN)
+# include <windows.h>
+#endif
+
+/// UserLockFile implements an atomic lock file
+/// that can be used as a mutex between different
+/// processes run by the same user.
+class UserLockFile {
+#if defined(Q_OS_WIN)
+	HANDLE m_handle;
+#endif
+	QString m_path;
+
+	public:
+		/// Constructs a LockFile at path.
+		/// The path should be somewhere
+		/// owned by the current user, such
+		/// as inside the home directory of
+		/// the user. This is to avoid clashing
+		/// with other lock files.
+		UserLockFile(const QString &path);
+
+		/// Destroys the LockFile, and ensures
+		/// that it is released.
+		~UserLockFile();
+
+		/// Returns the path that the lock file
+		/// exists at.
+		QString path() const;
+
+		/// Acquires the lock file.
+		bool acquire();
+
+		/// Releases the lock file.
+		void release();
+};
+
+#endif

src/mumble/UserLockFile_win.cpp

@@ -0,0 +1,73 @@
+/* Copyright (C) 2015, Mikkel Krautz <mikkel@krautz.dk>
+
+   All rights reserved.
+
+   Redistribution and use in source and binary forms, with or without
+   modification, are permitted provided that the following conditions
+   are met:
+
+   - Redistributions of source code must retain the above copyright notice,
+     this list of conditions and the following disclaimer.
+   - Redistributions in binary form must reproduce the above copyright notice,
+     this list of conditions and the following disclaimer in the documentation
+     and/or other materials provided with the distribution.
+   - Neither the name of the Mumble Developers nor the names of its
+     contributors may be used to endorse or promote products derived from this
+     software without specific prior written permission.
+
+   THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+   ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+   LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+   A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR
+   CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+   EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
+   PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
+   PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
+   LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
+   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+*/
+
+#include "mumble_pch.hpp"
+
+#include "UserLockFile.h"
+
+UserLockFile::UserLockFile(const QString &lockFilePath)
+	: m_handle(0)
+	, m_path(lockFilePath) {
+}
+
+UserLockFile::~UserLockFile() {
+	release();
+}
+
+QString UserLockFile::path() const {
+	return m_path;
+}
+
+bool UserLockFile::acquire() {
+	if (m_handle != 0) {
+		return false;
+	}
+
+	m_handle = CreateFile(
+		reinterpret_cast<const wchar_t *>(m_path.utf16()),
+		GENERIC_WRITE,
+		0,
+		NULL,
+		CREATE_ALWAYS,
+		FILE_ATTRIBUTE_HIDDEN,
+		NULL
+	);
+	if (m_handle == INVALID_HANDLE_VALUE && GetLastError() == ERROR_SHARING_VIOLATION) {
+		return false;
+	}
+	return true;
+}
+
+void UserLockFile::release() {
+	if (m_handle != 0) {
+		CloseHandle(m_handle);
+		m_handle = 0;
+	}
+}

src/mumble/main.cpp

@@ -58,6 +58,7 @@
 #include "MumbleApplication.h"
 #include "ApplicationPalette.h"
 #include "Themes.h"
+#include "UserLockFile.h"
 
 #if defined(USE_STATIC_QT_PLUGINS) && QT_VERSION < 0x050000
 Q_IMPORT_PLUGIN(qtaccessiblewidgets)
@@ -292,6 +293,25 @@ int main(int argc, char **argv) {
 		}
 	}
 
+#ifdef Q_OS_WIN
+	// The code above this block is somewhat racy, in that it might not
+	// be possible to do RPC/DBus if two processes start at almost the
+	// same time.
+	//
+	// In order to be completely sure we don't open multiple copies of
+	// Mumble, we open a lock file. The file is opened without any sharing
+	// modes enabled. This gives us exclusive access to the file.
+	// If another Mumble instance attempts to open the file, it will fail,
+	// and that instance will know to terminate itself.
+	UserLockFile userLockFile(g.qdBasePath.filePath(QLatin1String("mumble.lock")));
+	if (! bAllowMultiple) {
+		if (!userLockFile.acquire()) {
+			qWarning("Another process has already acquired the lock file at '%s'. Terminating...", qPrintable(userLockFile.path()));
+			return 1;
+		}
+	}
+#endif
+
 	// Load preferences
 	g.s.load();
 
@@ -553,6 +573,16 @@ int main(int argc, char **argv) {
 	google::protobuf::ShutdownProtobufLibrary();
 #endif
 #endif
+
+#ifdef Q_OS_WIN
+	// Release the userLockFile.
+	//
+	// It is important that we release it before we attempt to
+	// restart Mumble (if requested). If we do not release it
+	// before that, the new instance might not be able to start
+	// correctly.
+	userLockFile.release();
+#endif
 
 	// At this point termination of our process is immenent. We can safely
 	// launch another version of Mumble. The reason we do an actual

src/mumble/mumble.pro

@@ -370,8 +370,8 @@ win32 {
   } else {
     RC_FILE = mumble.rc
   }
-  HEADERS	*= GlobalShortcut_win.h Overlay_win.h TaskList.h
-  SOURCES	*= GlobalShortcut_win.cpp TextToSpeech_win.cpp Overlay_win.cpp SharedMemory_win.cpp Log_win.cpp os_win.cpp TaskList.cpp ../../overlay/HardHook.cpp ../../overlay/ods.cpp
+  HEADERS	*= GlobalShortcut_win.h Overlay_win.h TaskList.h UserLockFile.h
+  SOURCES	*= GlobalShortcut_win.cpp TextToSpeech_win.cpp Overlay_win.cpp SharedMemory_win.cpp Log_win.cpp os_win.cpp TaskList.cpp ../../overlay/HardHook.cpp ../../overlay/ods.cpp UserLockFile_win.cpp
   LIBS		*= -ldxguid -ldinput8 -lsapi -lole32 -lws2_32 -ladvapi32 -lwintrust -ldbghelp -llibsndfile-1 -lshell32 -lshlwapi -luser32 -lgdi32 -lpsapi
   LIBS		*= -ldelayimp -delayload:shell32.dll