task.h

#ifndef TASK_H
#define TASK_H

#include <QAtomicInt>
#include <QObject>

// Waits for a number of tasks to complete and emits allTasksDone() once all are
// complete.
class TaskWatcher : public QObject {
    Q_OBJECT
  public:
    TaskWatcher(QObject* pParent=NULL);
    virtual ~TaskWatcher();

    // Increment the number of active tasks by one and watch pTask for
    // doneSignal. This should be called before the task starts to prevent a
    // race condition where the task completes before we listen for doneSignal.
    void watchTask(QObject* pTask, const char* doneSignal);

  signals:
    // Signalled when all watched tasks are done from the thread that emitted
    // the last taskDone() signal.
    void allTasksDone();

  private slots:
    // Called when an individual task is done.
    // WARNING: Invoked in the thread the task runs in.
    void taskDone();

  private:
    QAtomicInt m_activeTasks;
};

#endif /* TASK_H */