Rework QWindowsPipeReader

The use of QWinOverlappedIoNotifier in QWindowsPipeReader restricts us
in the following ways:
  - The handle that gets assigned to QWinOverlappedIoNotifier is forever
    tied to an I/O completion port.
  - Other notification mechanisms like I/O completion routines of
    WriteFileEx do not work with such a handle.
  - No other QWinOverlappedIoNotifier can be registered for this handle.

To achieve the ultimate goal of making QWindowsPipeWriter thread-free
(to fix QTBUG-23378 and QTBUG-38185) we remove the usage of
QWinOverlappedIoNotifier from QWindowsPipeReader and use the
ReadFileEx API instead.
This has the additional advantage of removing the need for any thread
synchronization, as the I/O completion routine runs in the thread that
ReadFileEx was called on, leading to simpler and faster code.

Change-Id: I05c983e1f1e49d7dd27e3b77a47f87cae9c3f4c6
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

1 files changed, 20 insertions, 12 deletions

diff --git a/src/corelib/io/qwindowspipereader_p.h b/src/corelib/io/qwindowspipereader_p.h
index c8a66d9511..44009877f2 100644
--- a/src/corelib/io/qwindowspipereader_p.h
+++ b/src/corelib/io/qwindowspipereader_p.h
@@ -45,7 +45,6 @@
 // We mean it.
 //
 
-#include <qbytearray.h>
 #include <qobject.h>
 #include <private/qringbuffer_p.h>
 
@@ -53,9 +52,6 @@
 
 QT_BEGIN_NAMESPACE
 
-
-class QWinOverlappedIoNotifier;
-
 class Q_CORE_EXPORT QWindowsPipeReader : public QObject
 {
     Q_OBJECT
@@ -64,6 +60,7 @@ public:
     ~QWindowsPipeReader();
 
     void setHandle(HANDLE hPipeReadEnd);
+    void startAsyncRead();
     void stop();
 
     void setMaxReadBufferSize(qint64 size) { readBufferMaxSize = size; }
@@ -76,31 +73,42 @@ public:
     bool waitForReadyRead(int msecs);
     bool waitForPipeClosed(int msecs);
 
-    void startAsyncRead();
     bool isReadOperationActive() const { return readSequenceStarted; }
 
 Q_SIGNALS:
     void winError(ulong, const QString &);
     void readyRead();
     void pipeClosed();
-
-private Q_SLOTS:
-    void notified(quint32 numberOfBytesRead, quint32 errorCode, OVERLAPPED *notifiedOverlapped);
+    void _q_queueReadyRead(QPrivateSignal);
 
 private:
+    static void CALLBACK readFileCompleted(DWORD errorCode, DWORD numberOfBytesTransfered,
+                                           OVERLAPPED *overlappedBase);
+    void notified(DWORD errorCode, DWORD numberOfBytesRead);
     DWORD checkPipeState();
+    bool waitForNotification(int timeout);
+    void emitPendingReadyRead();
+
+    class Overlapped : public OVERLAPPED
+    {
+        Q_DISABLE_COPY(Overlapped)
+    public:
+        explicit Overlapped(QWindowsPipeReader *reader);
+        void clear();
+        QWindowsPipeReader *pipeReader;
+    };
 
-private:
     HANDLE handle;
-    OVERLAPPED overlapped;
-    QWinOverlappedIoNotifier *dataReadNotifier;
+    Overlapped overlapped;
     qint64 readBufferMaxSize;
     QRingBuffer readBuffer;
     qint64 actualReadBufferSize;
     bool stopped;
     bool readSequenceStarted;
+    bool notifiedCalled;
     bool pipeBroken;
-    bool readyReadEmitted;
+    bool readyReadPending;
+    bool inReadyRead;
 };
 
 QT_END_NAMESPACE