Allow QWindowsPipe{Reader|Writer} to work with foreign event loops, take 2

When a foreign event loop that does not enter an alertable wait state
is running (which is also the case when a native dialog window is
modal), pipe handlers would freeze temporarily due to their APC
callbacks not being invoked.

We address this problem by moving the I/O callbacks to the Windows
thread pool, and only posting completion events to the main loop
from there. That makes the actual I/O completely independent from
any main loop, while the signal delivery works also with foreign
loops (because Qt event delivery uses Windows messages, which foreign
loops typically handle correctly).

As a nice side effect, performance (and in particular scalability)
is improved.

Several other approaches have been tried:
1) Using QWinEventNotifier was about a quarter slower and scaled much
   worse. Additionally, it also required a rather egregious hack to
   handle the (pathological) case of a single thread talking to both
   ends of a QLocalSocket synchronously.
2) Queuing APCs from the thread pool to the main thread and also
   posting wake-up events to its event loop, and handling I/O on the
   main thread; this performed roughly like this solution, but scaled
   half as well, and the separate wake-up path was still deemed hacky.
3) Only posting wake-up events to the main thread from the thread pool,
   and still handling I/O on the main thread; this still performed
   comparably to 2), and the pathological case was not handled at all.
4) Using this approach for reads and that of 3) for writes was slightly
   faster with big amounts of data, but scaled slightly worse, and the
   diverging implementations were deemed not desirable.

Fixes: QTBUG-64443
Change-Id: I66443c3021d6ba98639a214c3e768be97d2cf14b
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

1 files changed, 23 insertions, 21 deletions

diff --git a/src/corelib/io/qwindowspipewriter_p.h b/src/corelib/io/qwindowspipewriter_p.h
index 39e8ffe40a..b648d7b846 100644
--- a/src/corelib/io/qwindowspipewriter_p.h
+++ b/src/corelib/io/qwindowspipewriter_p.h
@@ -1,6 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 Alex Trotsenko <alex1973tr@gmail.com>
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -54,7 +55,10 @@
 #include <QtCore/private/qglobal_p.h>
 #include <qelapsedtimer.h>
 #include <qobject.h>
-#include <qbytearray.h>
+#include <qdeadlinetimer.h>
+#include <qmutex.h>
+#include <private/qringbuffer_p.h>
+
 #include <qt_windows.h>
 
 QT_BEGIN_NAMESPACE
@@ -117,39 +121,37 @@ public:
     bool write(const QByteArray &ba);
     void stop();
     bool waitForWrite(int msecs);
-    bool isWriteOperationActive() const { return writeSequenceStarted; }
+    bool isWriteOperationActive() const;
     qint64 bytesToWrite() const;
 
 Q_SIGNALS:
     void canWrite();
     void bytesWritten(qint64 bytes);
-    void _q_queueBytesWritten(QPrivateSignal);
 
-private:
-    static void CALLBACK writeFileCompleted(DWORD errorCode, DWORD numberOfBytesTransfered,
-                                            OVERLAPPED *overlappedBase);
-    void notified(DWORD errorCode, DWORD numberOfBytesWritten);
-    bool waitForNotification(int timeout);
-    void emitPendingBytesWrittenValue();
+protected:
+    bool event(QEvent *e) override;
 
-    class Overlapped : public OVERLAPPED
-    {
-        Q_DISABLE_COPY_MOVE(Overlapped)
-    public:
-        explicit Overlapped(QWindowsPipeWriter *pipeWriter);
-        void clear();
-
-        QWindowsPipeWriter *pipeWriter;
-    };
+private:
+    void startAsyncWriteLocked();
+    static void CALLBACK waitCallback(PTP_CALLBACK_INSTANCE instance, PVOID context,
+                                      PTP_WAIT wait, TP_WAIT_RESULT waitResult);
+    bool writeCompleted(DWORD errorCode, DWORD numberOfBytesWritten);
+    bool waitForNotification(const QDeadlineTimer &deadline);
+    bool consumePendingAndEmit(bool allowWinActPosting);
 
     HANDLE handle;
-    Overlapped overlapped;
-    QByteArray buffer;
+    HANDLE eventHandle;
+    HANDLE syncHandle;
+    PTP_WAIT waitObject;
+    OVERLAPPED overlapped;
+    QRingBuffer writeBuffer;
     qint64 pendingBytesWrittenValue;
+    mutable QMutex mutex;
+    DWORD lastError;
     bool stopped;
     bool writeSequenceStarted;
-    bool notifiedCalled;
     bool bytesWrittenPending;
+    bool winEventActPosted;
     bool inBytesWritten;
 };