QSocketNotifier: extend API to provide more flexible startup

Technically, having a single constructor limits the use-cases for this
class. We should take into account that:

  - an opened socket descriptor must be available at the moment of
    construction;
  - the constructor unconditionally enables the notifier (the possible
    solution

        notifier = new QSocketNotifier(...);
        notifier->setEnabled(false);

    is suboptimal due to heavy operations inside the event dispatcher);
  - for these reasons, QSocketNotifier most often cannot be a member of
    another class (we have an extra allocation and indirect access).

This patch addresses this shortcoming by making it possible to set the
socket descriptor at a later point:

[ChangeLog][QtCore][QSocketNotifier] Added setSocket() and an additional
constructor which requires no socket.

Change-Id: I2eb2edf33ddafe99e528aac7d3774ade40795e7a
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/corelib/kernel/qsocketnotifier.h b/src/corelib/kernel/qsocketnotifier.h
index b8a5cc542a..fdf11961c3 100644
--- a/src/corelib/kernel/qsocketnotifier.h
+++ b/src/corelib/kernel/qsocketnotifier.h
@@ -54,12 +54,15 @@ class Q_CORE_EXPORT QSocketNotifier : public QObject
 public:
     enum Type { Read, Write, Exception };
 
+    explicit QSocketNotifier(Type, QObject *parent = nullptr);
     QSocketNotifier(qintptr socket, Type, QObject *parent = nullptr);
     ~QSocketNotifier();
 
+    void setSocket(qintptr socket, bool enable = false);
     qintptr socket() const;
     Type type() const;
 
+    bool isValid() const;
     bool isEnabled() const;
 
 public Q_SLOTS: