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author | Kai Koehne <kai.koehne@digia.com> | 2013-04-30 14:46:08 +0200 |
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committer | The Qt Project <gerrit-noreply@qt-project.org> | 2013-05-03 17:01:47 +0200 |
commit | 494c616951d41f2f394a7157f8970e14096f41b4 (patch) | |
tree | 9e42e9970b4b28809d97c0de94acc9fa7a81c54e /examples/serialport/doc/blockingmaster.qdoc | |
parent | bcdeb589dd9d3b0ff7270d380d043b1882eefdc0 (diff) |
Fix examples directory layout
Move examples into a dedicated 'serialport' directory. This is
in line with what the other modules do, and makes sure that
the examples show up in a sensible place even for the 'combined'
source packages.
Task-number: QTBUG-30912
Change-Id: Iefa2b634df3d2eb34f655b34f6fb24a224b78869
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Laszlo Papp <lpapp@kde.org>
Reviewed-by: Jerome Pasion <jerome.pasion@digia.com>
Diffstat (limited to 'examples/serialport/doc/blockingmaster.qdoc')
-rw-r--r-- | examples/serialport/doc/blockingmaster.qdoc | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/examples/serialport/doc/blockingmaster.qdoc b/examples/serialport/doc/blockingmaster.qdoc new file mode 100644 index 00000000..40ac0702 --- /dev/null +++ b/examples/serialport/doc/blockingmaster.qdoc @@ -0,0 +1,162 @@ +/**************************************************************************** +** +** Copyright (C) 2011 - 2012 Denis Shienkov <denis.shienkov@gmail.com> +** Contact: http://www.qt-project.org/legal +** +** This file is part of the documentation of the Qt Toolkit. +** +** $QT_BEGIN_LICENSE:FDL$ +** Commercial License Usage +** Licensees holding valid commercial Qt licenses may use this file in +** accordance with the commercial license agreement provided with the +** Software or, alternatively, in accordance with the terms contained in +** a written agreement between you and Digia. For licensing terms and +** conditions see http://qt.digia.com/licensing. For further information +** use the contact form at http://qt.digia.com/contact-us. +** +** GNU Free Documentation License Usage +** Alternatively, this file may be used under the terms of the GNU Free +** Documentation License version 1.3 as published by the Free Software +** Foundation and appearing in the file included in the packaging of +** this file. Please review the following information to ensure +** the GNU Free Documentation License version 1.3 requirements +** will be met: http://www.gnu.org/copyleft/fdl.html. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example blockingmaster + \title Blocking Master Example + \ingroup qtserialport-examples + + The Blocking Master example shows how to create a application for a + serial interface using QSerialPort's synchronous API in a non-GUI thread. + + \image blockingmaster-example.png Screenshot of the Blocking Master example + + QSerialPort supports two general programming approaches: + + \list + + \li \e{The asynchronous (non-blocking) approach.} Operations are scheduled + and performed when the control returns to Qt's event loop. QSerialPort emits + a signal when the operation is finished. For example, QSerialPort::write() + returns immediately. When the data is sent to the serial port, QSerialPort + emits \l{QSerialPort::bytesWritten()}{bytesWritten()}. + + \li \e{The synchronous (blocking) approach.} In non-GUI and multithreaded + applications, the \c waitFor...() functions can be called (i.e. + QSerialPort::waitReadyRead()) to suspend the calling thread until the + operation has completed. + + \endlist + + In this example, the synchronous approach is demonstrated. The + \l{terminal}{Simple Terminal} example illustrates the + asynchronous approach. + + The purpose of this example is to demonstrate a pattern that you can use + to simplify your serial programming code, without losing responsiveness + in your user interface. Use of Qt's blocking serial programming API often + leads to simpler code, but because of its blocking behavior, it should only + be used in non-GUI threads to prevent the user interface from freezing. + But contrary to what many think, using threads with QThread does not + necessarily add unmanagable complexity to your application. + + This application is a Master, that demonstrate the work paired with Slave + application \l{blockingslave}{Blocking Slave Example}. + + The Master application is initiate the transfer request via serial port to + the Slave application and wait for a response from it. + + We will start with the MasterThread class, which handles the serial + programming code. + + \snippet blockingmaster/masterthread.h 0 + + MasterThread is a QThread subclass that provides an API for scheduling + requests to Slave, and it has signals for delivering responses and reporting + errors. You can call transaction() to startup new master transaction with + desired request data and other parameters, and the result is delivered by + the response() signal. If any error occurs, the error() or timeout() signals + is emitted. + + It's important to notice that transaction() is called from the main, GUI + thread, but the request data and other parameters will be accessed from + MasterThread's thread. Because we will be reading and writing MasterThread's + data members from different threads concurrently, we use QMutex to + synchronize access. + + \snippet blockingmaster/masterthread.cpp 2 + + The transaction() function stores the serial port name, timeout and request + data, and we lock the mutex with QMutexLocker to protect this data. We then + start the thread, unless it is already running. We will come back to the + QWaitCondition::wakeOne() call later. + + \snippet blockingmaster/masterthread.cpp 4 + \snippet blockingmaster/masterthread.cpp 5 + + In the run() function, we start by acquiring the mutex lock, fetching the + serial port name, timeout and request data from the member data, and then + releasing the lock again. The case that we are protecting ourselves against + is that \c transaction() could be called at the same time as we are fetching + this data. QString is \l reentrant but \e not \l{thread-safe}, and we must + also avoid the unlikely risk of reading the serial port name from one request, + and timeout or request data of another. And as you might have guessed, + MasterThread can only handle one request at a time. + + The QSerialPort object we construct on stack into run() function before loop + enter: + + \snippet blockingmaster/masterthread.cpp 6 + + This allows us once to create an object, while running loop, and also means + that all the methods of the object will be executed in the context of the + run() thread. + + In the loop, we check for changed or not the name of serial port for the + current transaction. And if the name is changed then re-open and re-configure + the serial port. + + \snippet blockingmaster/masterthread.cpp 7 + + The loop will continue creating request data, write to serial port and wait + until all data is transferred. + + \snippet blockingmaster/masterthread.cpp 8 + + \warning The method waitForBytesWritten() should be used after each write() + call for the blocking approach, because it processes all the I/O routines + instead of Qt event-loop. + + The timeout() signal is emitted if error occurs when transferring data. + + \snippet blockingmaster/masterthread.cpp 9 + + After a successful request, we start wait until response and try read it. + + \snippet blockingmaster/masterthread.cpp 10 + + \warning The method waitForReadyRead() should be used before each read() + call for the blocking approach, because it processes all the I/O routines + instead of Qt event-loop. + + The timeout() signal is emitted if error occurs when receiving data. + + \snippet blockingmaster/masterthread.cpp 11 + + After a successful transaction is emitted response() signal containing the + data received from the Slave application: + + \snippet blockingmaster/masterthread.cpp 12 + + Next, the thread goes to sleep until the next transaction is appear. On + waking, the thread re-reads the new data of members and run loop from the + beginning. + + \snippet blockingmaster/masterthread.cpp 13 + + \sa {Simple Terminal Example}, {Blocking Slave Example} +*/ |