Hey there, let's break down the crash you're hitting in your Qt 5.10 crawler project—libcrypto's lh_insert() function crashing when using QNetworkAccessManager usually ties back to a few common issues, so let's work through them step by step:

1. Duplicate Signal-Slot Connections (Critical Fix!) #

Looking at your code snippet, you’re calling connect(manager, SIGNAL(finished(QNetworkReply*)),&loop, SLOT(quit())) inside your while(true) loop. This creates a new signal-slot binding every iteration, meaning each request finish will trigger the quit() slot multiple times. Over time, this builds up invalid bindings, leading to memory corruption and crashes in low-level libraries like OpenSSL.

Fix: Move the connect call outside the loop so it only runs once:

std::string result = "";
QUrl url(inURL.c_str());
jar->setCookiesFromUrl(list, url);

// Connect ONCE before entering the loop
QEventLoop loop;
connect(manager, &QNetworkAccessManager::finished, &loop, &QEventLoop::quit);

while(true){
    QNetworkRequest request = QNetworkRequest(url);
    QNetworkReply *netReply = manager->get(request);
    loop.exec();

    if(netReply->error() == QNetworkReply::NoError){
        result = netReply->readAll().toStdString();
        // Process your result here
    } else {
        qDebug() << "Request failed:" << netReply->errorString();
    }

    // Critical: Clean up the reply to avoid memory leaks
    netReply->deleteLater();

    // Add an exit condition here to prevent infinite loop!
    // if (someStopCondition) break;
}

2. OpenSSL Version Compatibility #

Qt 5.10 has specific dependencies on OpenSSL versions. If your system's libcrypto.so version doesn’t match the one Qt was compiled against, you can hit symbol conflicts or crashes in low-level SSL functions like lh_insert().

Check: Add this line to your code to verify Qt's SSL version:

qDebug() << "Qt SSL Library Version:" << QSslSocket::sslLibraryVersionString();

Compare this to your system's installed OpenSSL version (run openssl version in terminal). If they don’t align, either:

• Install the matching OpenSSL version for your Qt 5.10 build
• Recompile Qt with the OpenSSL version present on your system

3. Thread Safety Issues #

QNetworkAccessManager and QNetworkCookieJar are not thread-safe. If your crawler uses these objects across multiple threads (e.g., starting requests from a worker thread while the jar is accessed from the main thread), race conditions can corrupt OpenSSL's internal structures, triggering crashes in lh_insert().

Fix:

• Ensure all operations with manager and jar happen on the same thread
• If using multi-threading, move the entire network logic to a dedicated worker thread, and use signal-slot communication to pass data instead of directly accessing network objects

4. CookieJar Mismanagement #

If your QNetworkCookieJar (the jar variable) isn’t properly initialized, is deleted prematurely, or modified concurrently, it can pass invalid data to OpenSSL and cause crashes.

Check:

• Verify jar is a valid, non-null pointer before calling setCookiesFromUrl()
• If using a custom QNetworkCookieJar subclass, ensure all overridden methods (like cookiesForUrl() or setCookiesFromUrl()) are thread-safe
• Avoid modifying the cookie jar while requests are in flight

Start with fixing the duplicate signal-slot connection first—it’s the most likely culprit here. If that doesn’t resolve the crash, move on to checking OpenSSL compatibility and thread safety.

内容的提问来源于stack exchange，提问作者mkuhlmann