Avoid heap allocations in Median class

Create a MedianDouble class and V2 version of BlockSizeManager, which
use a fixed size array of double (since we always use 7 elements
to calculate the median anyway).

Change-Id: Ife90b90336a9a8c037b90726dee4cd2a1b8b6cd9
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

1 files changed, 52 insertions, 0 deletions

diff --git a/src/concurrent/qtconcurrentiteratekernel.cpp b/src/concurrent/qtconcurrentiteratekernel.cpp
index 49056406c3..3b9b186b39 100644
--- a/src/concurrent/qtconcurrentiteratekernel.cpp
+++ b/src/concurrent/qtconcurrentiteratekernel.cpp
@@ -182,6 +182,58 @@ int BlockSizeManager::blockSize()
     return m_blockSize;
 }
 
+/*! \internal
+
+*/
+BlockSizeManagerV2::BlockSizeManagerV2(int iterationCount)
+    : maxBlockSize(iterationCount / (QThreadPool::globalInstance()->maxThreadCount() * 2)),
+      beforeUser(0), afterUser(0),
+      m_blockSize(1)
+{ }
+
+// Records the time before user code.
+void BlockSizeManagerV2::timeBeforeUser()
+{
+    if (blockSizeMaxed())
+        return;
+
+    beforeUser = getticks();
+    controlPartElapsed.addValue(elapsed(beforeUser, afterUser));
+}
+
+ // Records the time after user code and adjust the block size if we are spending
+ // to much time in the for control code compared with the user code.
+void BlockSizeManagerV2::timeAfterUser()
+{
+    if (blockSizeMaxed())
+        return;
+
+    afterUser = getticks();
+    userPartElapsed.addValue(elapsed(afterUser, beforeUser));
+
+    if (controlPartElapsed.isMedianValid() == false)
+        return;
+
+    if (controlPartElapsed.median() * TargetRatio < userPartElapsed.median())
+        return;
+
+    m_blockSize = qMin(m_blockSize * 2,  maxBlockSize);
+
+#ifdef QTCONCURRENT_FOR_DEBUG
+    qDebug() << QThread::currentThread() << "adjusting block size" << controlPartElapsed.median() << userPartElapsed.median() << m_blockSize;
+#endif
+
+    // Reset the medians after adjusting the block size so we get
+    // new measurements with the new block size.
+    controlPartElapsed.reset();
+    userPartElapsed.reset();
+}
+
+int BlockSizeManagerV2::blockSize()
+{
+    return m_blockSize;
+}
+
 } // namespace QtConcurrent
 
 QT_END_NAMESPACE