QIODevice: implement a "zero-copy" strategy for buffered writes

It works as follows:

  - user calls write(const QByteArray &);
  - this function keeps a pointer to the chunk and calls a regular
    write(data, len);
  - write(data, len) calls a virtual writeData();
  - subclass calls a new QIODevicePrivate::write();
  - QIODevicePrivate::write() makes a shallow copy of
    the byte array.

Proposed solution is fully compatible with existing subclasses.
By replacing a call to d->writeBuffer.append() with d->write(),
subclasses can improve their performance.

Bump the TypeInformationVersion field in qtHookData, to notify the
Qt Creator developers that the offset of QFilePrivate::fileName was
changed and dumpers should be adapted.

Change-Id: I24713386cc74a9f37e5223c617e4b1ba97f968dc
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

1 files changed, 2 insertions, 2 deletions

diff --git a/tests/auto/other/toolsupport/tst_toolsupport.cpp b/tests/auto/other/toolsupport/tst_toolsupport.cpp
index 19b6adb4b3..fc3a13267e 100644
--- a/tests/auto/other/toolsupport/tst_toolsupport.cpp
+++ b/tests/auto/other/toolsupport/tst_toolsupport.cpp
@@ -126,9 +126,9 @@ void tst_toolsupport::offsets_data()
 #ifdef Q_PROCESSOR_X86
         // x86 32-bit has weird alignment rules. Refer to QtPrivate::AlignOf in
         // qglobal.h for more details.
-        data << 184 << 288;
+        data << 188 << 296;
 #else
-        data << 188 << 288;
+        data << 192 << 296;
 #endif
     }
 #endif