Issue with Unix signals and QTestStream readline

[foniwe]

Hello

The issue arises because QTextStream(stdin).readLine() is a blocking call, and signals like SIGTERM are not handled immediately during such operations. The signal handler will execute only after the blocking call completes.

Solution:
Use non-blocking I/O with QSocketNotifier to read from stdin asynchronously, allowing signals to be handled promptly:

#include <QCoreApplication>
#include <QSocketNotifier>
#include <QTextStream>
#include <signal.h>
 
QCoreApplication* app = nullptr;
 
void signalHandler(int) {
    if (app) app->quit();
}
 
int main(int argc, char* argv[]) {
    QCoreApplication application(argc, argv);
    app = &application;
 
    signal(SIGTERM, signalHandler); // Register signal handler
 
    QSocketNotifier notifier(STDIN_FILENO, QSocketNotifier::Read);
    QObject::connect(&notifier, &QSocketNotifier::activated, [&]() {
        QTextStream input(stdin);
        QString line = input.readLine();
        if (!line.isEmpty()) qDebug() << "Input:" << line;
    });
 
    return application.exec();
}

#include <QCoreApplication>
#include <QSocketNotifier>
#include <QTextStream>
#include <signal.h>

QCoreApplication* app = nullptr;

void signalHandler(int) {
    if (app) app->quit();
}

int main(int argc, char* argv[]) {
    QCoreApplication application(argc, argv);
    app = &application;

    signal(SIGTERM, signalHandler); // Register signal handler

    QSocketNotifier notifier(STDIN_FILENO, QSocketNotifier::Read);
    QObject::connect(&notifier, &QSocketNotifier::activated, [&]() {
        QTextStream input(stdin);
        QString line = input.readLine();
        if (!line.isEmpty()) qDebug() << "Input:" << line;
    });

    return application.exec();
}

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This ensures signal handling works even while waiting for input.