Reorder the members in QThreadData to avoid padding holes

Before this change, this struct had size 104 and a total of 21 padding
bytes. Now it's down to 88 bytes and only 5 bytes of padding.

pahole report on a 64-bit system:
    class QAtomicInt          _ref;                  /*     0     4 */
    /* XXX 4 bytes hole, try to pack */
public:
    class QThread *            thread;               /*     8     8 */
    HANDLE                     threadId;             /*    16     8 */
    bool                       quitNow;              /*    24     1 */
    /* XXX 3 bytes hole, try to pack */
    int                        loopLevel;            /*    28     4 */
    class QAtomicPointer<QAbstractEventDispatcher> eventDispatcher; /*    32     8 */
    class QStack<QEventLoop*> eventLoops;            /*    40     8 */
    /* --- cacheline 1 boundary (64 bytes) --- */
    class QPostEventList      postEventList;         /*    48    32 */
    bool                       canWait;              /*    80     1 */
    /* XXX 7 bytes hole, try to pack */
    class QVector<void*>      tls;                   /*    88     8 */
    bool                       isAdopted;            /*    96     1 */
    /* size: 104, cachelines: 2, members: 11 */
    /* sum members: 90, holes: 3, sum holes: 14 */
    /* padding: 7 */

Change-Id: I1fc88e0b312f38eccdea440734fd37e0519285a2
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>

2 files changed, 14 insertions, 10 deletions

diff --git a/src/corelib/thread/qthread.cpp b/src/corelib/thread/qthread.cpp
index 27529f8644..7667aff0b2 100644
--- a/src/corelib/thread/qthread.cpp
+++ b/src/corelib/thread/qthread.cpp
@@ -58,8 +58,8 @@ QT_BEGIN_NAMESPACE
 */
 
 QThreadData::QThreadData(int initialRefCount)
-    : _ref(initialRefCount), thread(0), threadId(0),
-      quitNow(false), loopLevel(0), eventDispatcher(0), canWait(true), isAdopted(false)
+    : _ref(initialRefCount), loopLevel(0), thread(0), threadId(0),
+      eventDispatcher(0), quitNow(false), canWait(true), isAdopted(false)
 {
     // fprintf(stderr, "QThreadData %p created\n", this);
 }
diff --git a/src/corelib/thread/qthread_p.h b/src/corelib/thread/qthread_p.h
index fa1f7414f1..8429e41433 100644
--- a/src/corelib/thread/qthread_p.h
+++ b/src/corelib/thread/qthread_p.h
@@ -219,8 +219,6 @@ public:
 
 class QThreadData
 {
-    QAtomicInt _ref;
-
 public:
     QThreadData(int initialRefCount = 1);
     ~QThreadData();
@@ -262,17 +260,23 @@ public:
         { return std::find(locations, locations + Count, method) != locations + Count; }
     };
 
-    QThread *thread;
-    Qt::HANDLE threadId;
-    bool quitNow;
+private:
+    QAtomicInt _ref;
+
+public:
     int loopLevel;
-    QAtomicPointer<QAbstractEventDispatcher> eventDispatcher;
+
     QStack<QEventLoop *> eventLoops;
     QPostEventList postEventList;
-    bool canWait;
+    QThread *thread;
+    Qt::HANDLE threadId;
+    QAtomicPointer<QAbstractEventDispatcher> eventDispatcher;
     QVector<void *> tls;
-    bool isAdopted;
     FlaggedDebugSignatures flaggedSignatures;
+
+    bool quitNow;
+    bool canWait;
+    bool isAdopted;
 };
 
 class QScopedLoopLevelCounter