/**************************************************************************** ** ** Copyright (C) 2011 - 2012 Denis Shienkov ** Copyright (C) 2012 - 2013 Laszlo Papp ** Copyright (C) 2016 The Qt Company Ltd. ** Contact: https://www.qt.io/licensing/ ** ** 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 The Qt Company. For licensing terms ** and conditions see https://www.qt.io/terms-conditions. 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Please review the following information to ensure ** the GNU Free Documentation License version 1.3 requirements ** will be met: https://www.gnu.org/licenses/fdl-1.3.html. ** $QT_END_LICENSE$ ** ****************************************************************************/ /*! \example blockingmaster \title Blocking Master Example \ingroup qtserialport-examples \brief Shows how to use the synchronous API of QSerialPort in a worker thread. \e{Blocking Master} shows how to create an application for a serial interface using the synchronous API of QSerialPort in a worker thread. \image blockingmaster-example.png QSerialPort supports two programming alternatives: \list \li \e{The asynchronous (non-blocking) alternative.} Operations are scheduled and performed when the control returns to the Qt event loop. The QSerialPort class emits a signal when the operation is finished. For example, the \l{QIODevice::write()}{write()} method returns immediately. When the data is sent to the serial port, the QSerialPort class emits the \l{QIODevice::bytesWritten()}{bytesWritten()} signal. \li \e{The synchronous (blocking) alternative.} In headless and multithreaded applications, the wait method can be called (in this case, \l{QSerialPort::waitForReadyRead()}{waitForReadyRead()}) to suspend the calling thread until the operation has completed. \endlist In this example, the synchronous alternative is demonstrated. The \l{terminal}{Terminal} example illustrates the asynchronous alternative. The purpose of this example is to demonstrate how to simplify your serial programming code without losing the responsiveness of the user interface. The blocking serial programming API often leads to simpler code, but it should only be used in non-GUI threads to keep the user interface responsive. This application is the master which demonstrates the work paired with the slave application \l{blockingslave}{Blocking Slave Example}. The master application initiates the transfer request via the serial port to the slave application and waits for response. \snippet blockingmaster/masterthread.h 0 MasterThread is a QThread subclass that provides API for scheduling requests to the slave. This class provides signals for responding and reporting errors. The transaction() method can be called to start up the new master transaction with the desired request. The result is provided by the response() signal. In case of any issues, the error() or timeout() signal is emitted. Note, the transaction() method is called in the main thread, but the request is provided in the MasterThread thread. The MasterThread data members are read and written concurrently in different threads, thus the QMutex class is used to synchronize the access. \snippet blockingmaster/masterthread.cpp 2 The transaction() method stores the serial port name, timeout and request data. The mutex can be locked with QMutexLocker to protect this data. The thread can be started then, unless it is already running. The \l{QWaitCondition::wakeOne()}{wakeOne()} method is discussed later. \snippet blockingmaster/masterthread.cpp 4 \snippet blockingmaster/masterthread.cpp 5 In the run() function, the first is to lock the QMutex object, then fetch the serial port name, timeout and request data by using the member data. Having that done, the QMutex lock is released. Under no circumstance should the \c transaction() method be called simultaneously with a process fetching the data. Note, while the QString class is reentrant, it is not thread-safe. Thereby, it is not recommended to read the serial port name in a request thread, and timeout or request data in another thread. The MasterThread class can only handle one request at a time. The QSerialPort object is constructed on stack in the run() method before entering the loop: \snippet blockingmaster/masterthread.cpp 6 This makes it possible to create an object while running the loop. It also means that all the object methods are executed in the scope of the run() method. It is checked inside the loop whether or not the serial port name of the current transaction has changed. If this has changed, the serial port is reopened and then reconfigured. \snippet blockingmaster/masterthread.cpp 7 The loop will continue to request data, write to the serial port and wait until all data is transferred. \snippet blockingmaster/masterthread.cpp 8 \warning As for the blocking transfer, the \l{QSerialPort::waitForBytesWritten()}{waitForBytesWritten()} method should be used after each \l{QIODevice::write()}{write} method call. This will process all the I/O routines instead of the Qt event loop. The timeout() signal is emitted if a timeout error occurs when transferring data. \snippet blockingmaster/masterthread.cpp 9 There is a waiting period for response after a successful request, and then it is read again. \snippet blockingmaster/masterthread.cpp 10 \warning As for the blocking alternative, the \l{QSerialPort::waitForReadyRead()}{waitForReadyRead()} method should be used before each read() call. This will processes all the I/O routines instead of the Qt event loop. The timeout() signal is emitted if a timeout error occurs when receiving data. \snippet blockingmaster/masterthread.cpp 11 When a transaction has been completed successfully, the response() signal contains the data received from the slave application: \snippet blockingmaster/masterthread.cpp 12 Afterwards, the thread goes to sleep until the next transaction appears. The thread reads the new data after waking up by using the members and runs the loop from the beginning. \snippet blockingmaster/masterthread.cpp 13 \sa {Terminal Example}, {Blocking Slave Example} \include examples-run.qdocinc */