Base: Fix possible race condition when restarting the application

When restarting the application (e.g. after installing an addon) the application will be closed and a new instance will be launched. Now it can happen that the old instance is still busy writing the config files to disk while the new instance wants to read them in. At this time it's possible that a config file is in an invalid state so that the new instance will ignore it but then starts with a default configuration.
Later when closing the new instance the config files will be overwritten and destroy the user's original settings.

By using a lock file this race condition will be avoided. It uses a timeout of 1 second that should be enough for the old instance to write the files to disk.

src/Base/Parameter.cpp

@@ -41,6 +41,10 @@
 #include <utility>
 #endif
 
+#include <QFileInfo>
+#include <QLockFile>
+#include <QDir>
+
 #ifdef FC_OS_LINUX
 #include <unistd.h>
 #endif
@@ -1719,6 +1723,17 @@ void ParameterManager::SaveDocument() const
     }
 }
 
+namespace
+{
+void waitForFileAccess(const Base::FileInfo& file)
+{
+    QFileInfo fi(QDir::tempPath(), QString::fromStdString(file.fileName() + ".lock"));
+    QLockFile lock(fi.absoluteFilePath());
+    const int waitOneSecond = 1000;
+    lock.tryLock(waitOneSecond);
+}
+}  // namespace
+
 //**************************************************************************
 // Document handling
 
@@ -1736,9 +1751,9 @@ bool ParameterManager::LoadOrCreateDocument(const char* sFileName)
 
 int ParameterManager::LoadDocument(const char* sFileName)
 {
-    Base::FileInfo file(sFileName);
-
     try {
+        Base::FileInfo file(sFileName);
+        waitForFileAccess(file);
 #if defined(FC_OS_WIN32)
         std::wstring name = file.toStdWString();
         // NOLINTNEXTLINE(cppcoreguidelines-pro-type-reinterpret-cast)
@@ -1828,9 +1843,9 @@ int ParameterManager::LoadDocument(const XERCES_CPP_NAMESPACE_QUALIFIER InputSou
 
 void ParameterManager::SaveDocument(const char* sFileName) const
 {
-    Base::FileInfo file(sFileName);
-
     try {
+        Base::FileInfo file(sFileName);
+        waitForFileAccess(file);
         //
         // Plug in a format target to receive the resultant
         // XML stream from the serializer.

tests/src/Base/Parameter.cpp

@@ -1,5 +1,6 @@
 #include "gtest/gtest.h"
 #include <boost/core/ignore_unused.hpp>
+#include <QLockFile>
 #include <Base/FileInfo.h>
 #include <Base/Parameter.h>
 
@@ -442,4 +443,23 @@ TEST_F(ParameterTest, TestObserverNoRef)
     EXPECT_EQ(obs.getCountNotifications(), 1);
 }
 
+TEST_F(ParameterTest, TestLockFile)
+{
+    std::string fn = getFileName();
+    fn.append(".lock");
+
+    QLockFile lockFile1(QString::fromStdString(fn));
+    EXPECT_TRUE(lockFile1.tryLock(100));
+    EXPECT_TRUE(lockFile1.isLocked());
+
+    QLockFile lockFile2(QString::fromStdString(fn));
+    EXPECT_FALSE(lockFile2.tryLock(100));
+    EXPECT_FALSE(lockFile2.isLocked());
+
+    lockFile1.unlock();
+    EXPECT_TRUE(lockFile2.lock());
+    EXPECT_FALSE(lockFile1.tryLock(500));
+    lockFile2.unlock();
+}
+
 // NOLINTEND(cppcoreguidelines-*,readability-*)