QRingBuffer: avoid allocation in c'tor

Reduces creation time and memory consumption when the buffer is unused.
Robin's benchmark:

  QBENCHMARK {
      QFile file(filename);
  }

reports the following results (run with -median 10 -iterations 524288):

before: 0.00028 msecs per iteration (total: 149, iterations: 524288)
after:  0.00017 msecs per iteration (total: 93, iterations: 524288).

Change-Id: Ied4e7caeca794b94260b8fc59b3ba656f4719c30
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/src/corelib/tools/qringbuffer_p.h b/src/corelib/tools/qringbuffer_p.h
index e7e80bc02c..3a5ae1c4cc 100644
--- a/src/corelib/tools/qringbuffer_p.h
+++ b/src/corelib/tools/qringbuffer_p.h
@@ -54,9 +54,7 @@ class QRingBuffer
 {
 public:
     explicit inline QRingBuffer(int growth = 4096) :
-        head(0), tail(0), tailBuffer(0), basicBlockSize(growth), bufferSize(0) {
-        buffers.append(QByteArray());
-    }
+        head(0), tail(0), tailBuffer(0), basicBlockSize(growth), bufferSize(0) { }
 
     inline qint64 nextDataBlockSize() const {
         return (tailBuffer == 0 ? tail : buffers.first().size()) - head;