Optimize access to the write buffer

Earlier for writing in writeBuffer was used the
QSerialPortPrivate::writeToBuffer() method which contained
a similar code for each platform.

Therefore it is reasonable to delete this method, and to move
its common functionality to the QSerialPort::writeData(). Also
all platform-dependent code of start of data transfer move to
the QSerialPortPrivate::startWriting() method.

Change-Id: I1423723fd69c05df974f8ba597e3dd71d5a797dd
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>
Reviewed-by: Denis Shienkov <denis.shienkov@gmail.com>

8 files changed, 13 insertions, 36 deletions

diff --git a/src/serialport/qserialport.cpp b/src/serialport/qserialport.cpp
index 5d9442e..cd0c681 100644
--- a/src/serialport/qserialport.cpp
+++ b/src/serialport/qserialport.cpp
@@ -1375,7 +1375,11 @@ qint64 QSerialPort::readLineData(char *data, qint64 maxSize)
 qint64 QSerialPort::writeData(const char *data, qint64 maxSize)
 {
     Q_D(QSerialPort);
-    return d->writeToBuffer(data, maxSize);
+
+    ::memcpy(d->writeBuffer.reserve(maxSize), data, maxSize);
+    if (!d->writeBuffer.isEmpty())
+        d->startWriting();
+    return maxSize;
 }
 
 void QSerialPort::setError(QSerialPort::SerialPortError serialPortError, const QString &errorString)
diff --git a/src/serialport/qserialport_symbian.cpp b/src/serialport/qserialport_symbian.cpp
index 6047793..9318696 100644
--- a/src/serialport/qserialport_symbian.cpp
+++ b/src/serialport/qserialport_symbian.cpp
@@ -248,10 +248,9 @@ qint64 QSerialPortPrivate::systemOutputQueueSize () const
     return 0;
 }
 
-qint64 QSerialPortPrivate::writeToBuffer(const char *data, qint64 maxSize)
+void QSerialPortPrivate::startWriting()
 {
     // TODO: Implement me
-    return -1;
 }
 
 bool QSerialPortPrivate::waitForReadyRead(int msec)
diff --git a/src/serialport/qserialport_symbian_p.h b/src/serialport/qserialport_symbian_p.h
index 253aa11..7c3d3ef 100644
--- a/src/serialport/qserialport_symbian_p.h
+++ b/src/serialport/qserialport_symbian_p.h
@@ -72,7 +72,7 @@ public:
     qint64 systemInputQueueSize () const;
     qint64 systemOutputQueueSize () const;
 
-    qint64 writeToBuffer(const char *data, qint64 maxSize);
+    void startWriting();
 
     bool waitForReadyRead(int msec);
     bool waitForBytesWritten(int msec);
diff --git a/src/serialport/qserialport_unix.cpp b/src/serialport/qserialport_unix.cpp
index 9571767..b994a0e 100644
--- a/src/serialport/qserialport_unix.cpp
+++ b/src/serialport/qserialport_unix.cpp
@@ -414,20 +414,10 @@ qint64 QSerialPortPrivate::systemOutputQueueSize () const
     return nbytes;
 }
 
-qint64 QSerialPortPrivate::writeToBuffer(const char *data, qint64 maxSize)
+void QSerialPortPrivate::startWriting()
 {
-    char *ptr = writeBuffer.reserve(maxSize);
-    if (maxSize == 1)
-        *ptr = *data;
-    else
-        ::memcpy(ptr, data, maxSize);
-
-    const qint64 written = maxSize;
-
-    if (!writeBuffer.isEmpty() && !isWriteNotificationEnabled())
+    if (!isWriteNotificationEnabled())
         setWriteNotificationEnabled(true);
-
-    return written;
 }
 
 bool QSerialPortPrivate::waitForReadyRead(int msecs)
diff --git a/src/serialport/qserialport_unix_p.h b/src/serialport/qserialport_unix_p.h
index dba0ac5..7dbb760 100644
--- a/src/serialport/qserialport_unix_p.h
+++ b/src/serialport/qserialport_unix_p.h
@@ -111,7 +111,7 @@ public:
     qint64 systemInputQueueSize () const;
     qint64 systemOutputQueueSize () const;
 
-    qint64 writeToBuffer(const char *data, qint64 maxSize);
+    void startWriting();
 
     bool waitForReadyRead(int msecs);
     bool waitForBytesWritten(int msecs);
diff --git a/src/serialport/qserialport_win.cpp b/src/serialport/qserialport_win.cpp
index ecbfa39..f9e8a5e 100644
--- a/src/serialport/qserialport_win.cpp
+++ b/src/serialport/qserialport_win.cpp
@@ -354,18 +354,10 @@ qint64 QSerialPortPrivate::systemOutputQueueSize ()
 
 #ifndef Q_OS_WINCE
 
-qint64 QSerialPortPrivate::writeToBuffer(const char *data, qint64 maxSize)
+void QSerialPortPrivate::startWriting()
 {
-    char *ptr = writeBuffer.reserve(maxSize);
-    if (maxSize == 1)
-        *ptr = *data;
-    else
-        ::memcpy(ptr, data, maxSize);
-
     if (!writeSequenceStarted)
         startAsyncWrite();
-
-    return maxSize;
 }
 
 bool QSerialPortPrivate::waitForReadyRead(int msecs)
diff --git a/src/serialport/qserialport_win_p.h b/src/serialport/qserialport_win_p.h
index 9876fe4..3ccdb56 100644
--- a/src/serialport/qserialport_win_p.h
+++ b/src/serialport/qserialport_win_p.h
@@ -81,7 +81,7 @@ public:
     qint64 systemInputQueueSize ();
     qint64 systemOutputQueueSize ();
 
-    qint64 writeToBuffer(const char *data, qint64 maxSize);
+    void startWriting();
 
     bool waitForReadyRead(int msec);
     bool waitForBytesWritten(int msec);
diff --git a/src/serialport/qserialport_wince.cpp b/src/serialport/qserialport_wince.cpp
index 26ebf64..bb76465 100644
--- a/src/serialport/qserialport_wince.cpp
+++ b/src/serialport/qserialport_wince.cpp
@@ -253,18 +253,10 @@ bool QSerialPortPrivate::clear(QSerialPort::Directions directions)
     return ::PurgeComm(descriptor, flags);
 }
 
-qint64 QSerialPortPrivate::writeToBuffer(const char *data, qint64 maxSize)
+void QSerialPortPrivate::startWriting()
 {
-    char *ptr = writeBuffer.reserve(maxSize);
-    if (maxSize == 1)
-        *ptr = *data;
-    else
-        ::memcpy(ptr, data, maxSize);
-
     // trigger write sequence
     notifyWrite();
-
-    return maxSize;
 }
 
 bool QSerialPortPrivate::waitForReadyRead(int msec)