fix spurious QWindowsPipeWriter deadlock

We must check the return value of CancelIo(Ex) and only wait for a
notification if it was successful.
CancelIoEx can fail, if the handle is closed before the
QWindowsPipeWriter destructor is called.

Change-Id: I2dcc97052be917c69d18c277856374cbc07e2169
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>

1 files changed, 7 insertions, 5 deletions

diff --git a/src/corelib/io/qwindowspipereader.cpp b/src/corelib/io/qwindowspipereader.cpp
index efadb357a9..2cb5845768 100644
--- a/src/corelib/io/qwindowspipereader.cpp
+++ b/src/corelib/io/qwindowspipereader.cpp
@@ -64,7 +64,7 @@ QWindowsPipeReader::QWindowsPipeReader(QObject *parent)
     connect(dataReadNotifier, &QWinOverlappedIoNotifier::notified, this, &QWindowsPipeReader::notified);
 }
 
-static void qt_cancelIo(HANDLE handle, OVERLAPPED *overlapped)
+static bool qt_cancelIo(HANDLE handle, OVERLAPPED *overlapped)
 {
     typedef BOOL (WINAPI *PtrCancelIoEx)(HANDLE, LPOVERLAPPED);
     static PtrCancelIoEx ptrCancelIoEx = 0;
@@ -74,16 +74,18 @@ static void qt_cancelIo(HANDLE handle, OVERLAPPED *overlapped)
             ptrCancelIoEx = PtrCancelIoEx(GetProcAddress(kernel32, "CancelIoEx"));
     }
     if (ptrCancelIoEx)
-        ptrCancelIoEx(handle, overlapped);
+        return ptrCancelIoEx(handle, overlapped);
     else
-        CancelIo(handle);
+        return CancelIo(handle);
 }
 
 QWindowsPipeReader::~QWindowsPipeReader()
 {
     if (readSequenceStarted) {
-        qt_cancelIo(handle, &overlapped);
-        dataReadNotifier->waitForNotified(-1, &overlapped);
+        if (qt_cancelIo(handle, &overlapped))
+            dataReadNotifier->waitForNotified(-1, &overlapped);
+        else
+            qErrnoWarning("QWindowsPipeReader: qt_cancelIo on handle %x failed.", handle);
     }
 }