feat: add single instance lock mechanism for fcitx5-helper (#105)

- Implement setSingleInstance() function to prevent multiple instances per user
- Add lock file management with proper cleanup on exit and signal handling
- Include signal handler cleanup for lock file when receiving SIGTERM from init

Log: add single instance lock mechanism for fcitx5-helper

Author: wyu71

src/fcitx5helper/main.cpp

@@ -7,14 +7,61 @@
 Q_LOGGING_CATEGORY(fcitx5Helper, "fcitx5.helper")
 
 #include <QCoreApplication>
+#include <QDir>
+#include <QLockFile>
+#include <QScopedPointer>
+#include <unistd.h>
 
 #include <signal.h>
 
+static QScopedPointer<QLockFile> g_lockFile;
+
+// Extract from DGuiApplicationHelper::setSingleInstance (UserScope only)
+static bool setSingleInstance() {
+    QString socket_key = "_fcitx5_single_instance_";
+    socket_key += QString("%1_").arg(getuid());
+    socket_key += QString("fcitx5-helper");
+
+    QString lockfile = socket_key;
+    if (!lockfile.startsWith(QLatin1Char('/'))) {
+        lockfile = QDir::cleanPath(QDir::tempPath());
+        lockfile += QLatin1Char('/') + socket_key;
+        qCDebug(fcitx5Helper) << "lockfile:" << lockfile;
+    }
+    lockfile += QStringLiteral(".lock");
+
+    qint64 pid = -1;
+    QString hostname, appname;
+    if (!g_lockFile.isNull() && g_lockFile->isLocked() && g_lockFile->getLockInfo(&pid, &hostname, &appname) && pid == getpid()) {
+        qCWarning(fcitx5Helper) << "call setSingleInstance again within the same process";
+        g_lockFile->unlock();
+        g_lockFile.reset();
+        qCDebug(fcitx5Helper) << "unlock lock file";
+    }
+
+    // Create new lock file
+    g_lockFile.reset(new QLockFile(lockfile));
+
+    // Try to lock
+    if (!g_lockFile->tryLock()) {
+        qCInfo(fcitx5Helper) << "fcitx5-helper instance already exists for current user, exiting";
+        return false;
+    }
+
+    qCDebug(fcitx5Helper) << "Created lock file:" << lockfile;
+    return true;
+}
+
 static void signal_callback_handler(int signum, siginfo_t *siginfo, void *context) {
     Q_UNUSED(context)
     qCDebug(fcitx5Helper) << "Received signal:" << signum << "from pid:" << (long)siginfo->si_pid;
     if (signum == SIGTERM && (long)siginfo->si_pid == 1) {
         qCInfo(fcitx5Helper) << "Terminating fcitx5 processes due to SIGTERM from init";
+        // Clean up lock file
+        if (!g_lockFile.isNull() && g_lockFile->isLocked()) {
+            qCInfo(fcitx5Helper) << "unlock lock file";
+            g_lockFile->unlock();
+        }
         QString output, error;
         ProcessMonitor::exeCommand("pidof fcitx5 | xargs kill -9", QStringList(), output, error);
         qCDebug(fcitx5Helper) << "Command output:" << output << "Error:" << error;
@@ -23,7 +70,7 @@ static void signal_callback_handler(int signum, siginfo_t *siginfo, void *contex
 }
 
 static void setupSignalHandler() {
-    //进城被init杀死，视为关机
+    //进程被init杀死，视为关机
     struct sigaction act;
     memset(&act, 0, sizeof(act));
     act.sa_sigaction = &signal_callback_handler;
@@ -34,11 +81,24 @@ static void setupSignalHandler() {
 int main(int argc, char *argv[])
 {
     qCInfo(fcitx5Helper) << "Starting fcitx5 helper process";
+    // Check single instance for current user
+    if (!setSingleInstance()) {
+        qCInfo(fcitx5Helper) << "fcitx5-helper already running";
+        return 0;
+    }
     QCoreApplication app(argc, argv);
 
+    // Register cleanup function to unlock on exit
+    QObject::connect(&app, &QCoreApplication::aboutToQuit, []() {
+        if (!g_lockFile.isNull() && g_lockFile->isLocked()) {
+            qCInfo(fcitx5Helper) << "unlock lock file";
+            g_lockFile->unlock();
+        }
+    });
+
     qCDebug(fcitx5Helper) << "Setting up signal handlers";
     setupSignalHandler();
-    
+
     qCDebug(fcitx5Helper) << "Initializing process monitor";
     ProcessMonitor monitor;
     monitor.startMonitoring();