Toggle or stop download thread-safely

ariadownloader.cpp

@@ -20,6 +20,12 @@
 #include "ariadownloader.h"
 #include "system.h"
 
+// libaria2 thread safety note:
+// "Please keep in mind that only one Session object can be allowed per process due to the heavy use
+// of static objects in aria2 code base. Session object is not safe for concurrent accesses from
+// multiple threads. It must be used from one thread at a time. In general, libaria2 is not entirely
+// thread-safe."
+
 int downloadEventCallback(aria2::Session* session, aria2::DownloadEvent event,
                           aria2::A2Gid gid, void* userData)
 {

downloadworker.cpp

@@ -21,6 +21,7 @@
 #include "quazip/quazip/JlCompress.h"
 #include "settings.h"
 #include "system.h"
+#include <QApplication>
 #include <QDebug>
 #include <QDir>
 
@@ -149,6 +150,8 @@ void DownloadWorker::download()
     auto start = std::chrono::steady_clock::now();
     bool ret = true;
     running_ = true;
+    // If the download is not making any progress, aria sleeps for 1 second each time it is called
+    // with RUN_ONCE. So this will not spin the CPU.
     while (ret && running_) {
         ret = downloader_.run();
         auto now = std::chrono::steady_clock::now();
@@ -175,7 +178,12 @@ void DownloadWorker::download()
                 emit completedSizeChanged(completedSize_);
             }
         }
+
+        // Respond to Qt signals sent to the downloader thread, namely toggle or stop
+        QApplication::processEvents();
     }
+
+    qDebug() << "Download loop exiting";
 }
 
 void DownloadWorker::toggle()

downloadworker.h

@@ -40,11 +40,11 @@ class DownloadWorker : public QObject, public AriaDownloader::DownloadCallback
     void addTorrent(const std::string& uri);
     void setDownloadDirectory(const std::string& dir);
     void setConnectUrl(const QString& url);
-    void toggle();
-    void stop();
 
 public slots:
     void download();
+    void toggle();
+    void stop();
 
 signals:
     void downloadSpeedChanged(int speed);

qmldownloader.cpp

@@ -18,6 +18,7 @@
 #include <QDir>
 #include <QApplication>
 #include <QDebug>
+#include <QMetaObject>
 
 #include "qmldownloader.h"
 #include "system.h"
@@ -181,15 +182,15 @@ void QmlDownloader::toggleDownload(QString installPath)
         startUpdate(installPath);
         return;
     }
-    worker_->toggle();
+    QMetaObject::invokeMethod(worker_, "toggle");
     setState(state() == DOWNLOADING ? PAUSED : DOWNLOADING);
 }
 
 void QmlDownloader::stopAria()
 {
     if (worker_) {
         qDebug() << "Stopping downloader thread";
-        worker_->stop();
+        QMetaObject::invokeMethod(worker_, "stop");
         thread_.quit();
         thread_.wait();
         worker_ = nullptr;