Qt inter-process communication

The traditional inter-process communication mode (shared memory...) can still be used in QT ..)
· In the desktop environment, a more convenient and Object-Oriented communication mode is developed based on the traditional inter-process communication mode.
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KDE environment: dcop
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GNOME Environment: bonobo
· Mechanism: the Linux IPC communication mechanism of the freedesktop open-source project. Both KDE and gnome environments support
· QT embedded defines a lightweight inter-process communication mechanism qcop.

Qcop:
· Qcop is implemented using the qcopchannel class.
· Qcopchannel inherited from the qobject class
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Provides the static function send () to send messages and data to be transmitted.
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The static function isregistered () is used to query whether a channel has been registered.
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When receiving messages and data from a channel, we need to construct a sub-class of qcopchannel and rewrite the receive () function, or provide a slot and use the connect () function to send the receive () signal connection
· Using qcop can easily combine the QT signal and slot mechanism, making it very convenient to use
· However, for communications between non-QT programs and QT programs, only other IPC methods can be used
QcopExample:
Send messages and data in a process:

Qbytearray data; Qdatastream out (& Data, qiodevice: writeonly ); Out <celnum; Qcopchannel: Send ("/system/temperature", "convertceltofah (INT)", data );

Receive messages and data in another process:

Qcopchannel * channel = new qcopchannel ("/system/temperature", this ); Connect (Channel, signal (received (const qstring &, constqbytearray &), this, slot (handlemsg (const qstring &, const qbytearray &)));

The following is an example:

// Copserv. h Run as a server-qws # Ifndef conversion_screen_h # Define conversion_screen_h # Include <qwidget> Class copserv: Public qwidget { Q_object Public: Copserv (); ~ Copserv (){}; Private slots: Void launchfah (); Void launchcel (); PRIVATE: Void createscreen (); Void launchapp (const char * path ); }; # Endif // conversion_screen_h // Copserv. cpp Program subject # Include <qpushbutton> # Include <qslider> # Include <qlabel> # Include <qdial> # Include <qlcdnumber> # Include <qvboxlayout> # Include <qhboxlayout> # Include <qgridlayout> # Include <qsettings> # Include <qapplication> # Include <qcoreapplication> # Include <unistd. h> # Include <sys/types. h> # Include "copserv. H" Copserv: copserv (): qwidget () { Createscreen (); } Void copserv: createscreen () { Qpushbutton * celbtn = new qpushbutton ("cel "); Qpushbutton * fahbtn = new qpushbutton ("Fah "); Qpushbutton * quitbtn = new qpushbutton ("quit "); Qgridlayout * mainlayout = new qgridlayout; Mainlayout-> addwidget (celbtn, 0, 0 ); Mainlayout-> addwidget (fahbtn, 0, 1 ); Mainlayout-> addwidget (quitbtn, 1, 0 ); Setlayout (mainlayout ); Connect (celbtn, signal (clicked (), this, slot (launchcel ())); Connect (fahbtn, signal (clicked (), this, slot (launchfah ())); Connect (quitbtn, signal (clicked (), qapp, slot (quit ())); Setgeometry (0, 50,240,320 ); Setwindowtitle ("server window "); } Void copserv: launchapp (const char * path) // Start the subroutine { If (Path = NULL) { Qdebug ("launch path is null! /N "); } Pid_t pid = fork (); // Create a sub-process If (pid = 0) { Qdebug ("New Process forked. PID is: % d/N", getpid ()); Int result = execl (path, path, 0 ); If (result <0) { Qdebug ("failed to launch application! /N "); } _ Exit (-1 ); } } Void copserv: launchcel () { Launchapp ("./CEL "); } Void copserv: launchfah () { Launchapp ("./Fah "); } // Main. cpp # Include <qapplication> # Include "copserv. H" Int main (INT argc, char * argv []) { Qapplication app (argc, argv, qapplication: guiserver ); Copserv screen; // Screen. setgeometry (0, 0,240,320 ); Screen. Show (); Return app.exe C (); }

// Cel. h // Header file of subroutine 1 # Ifndef cel_h # Define cel_h # Include <qwidget> Class qslider; Class qhboxlayout; Class cel: Public qwidget { Q_object Public: Cel (); ~ Cel (){}; Private slots: Void handlemsg (const qstring & message, const qbytearray & data ); Void sendmsg (INT celnum ); // Slot PRIVATE: Void fahtocel (INT fahnum ); Void createscreen (); Void createcel (); Void listenchannel (); Qslider * slider; Qhboxlayout * cellayout; }; // Cel. cpp # Endif // cel_h # Include <qpushbutton> # Include <qslider> # Include <qlabel> # Include <qlcdnumber> # Include <qvboxlayout> # Include <qhboxlayout> # Include <qapplication> # Include <qcopchannel> # Include <qdatastream> # Include <qbytearray> # Include "cel. H" Cel: cel (): qwidget () { Createscreen (); Listenchannel (); } Void cel: createscreen () { Qpushbutton * quitbtn = new qpushbutton ("quit "); Createcel (); Qvboxlayout * mainlayout = new qvboxlayout; Mainlayout-> addwidget (quitbtn ); Mainlayout-> addlayout (cellayout ); Setlayout (mainlayout ); Slider-> setfocus (); Connect (quitbtn, signal (clicked (), qapp, slot (quit ())); Setwindowtitle ("Celsius "); } Void cel: createcel () { Slider = new qslider (QT: vertical ); Slider-> setrange (0,100 ); Slider-> setvalue (0 ); Slider-> settickposition (qslider: ticksleft ); Qlabel * cellabel = new qlabel ("0 "); Cellayout = new qhboxlayout; Cellayout-> addwidget (cellabel, 0, QT: alignright ); Cellayout-> addwidget (slider, 0, QT: alignleft ); Cellayout-> setspacing (10 ); Connect (slider, signal (valuechanged (INT), cellabel, slot (setnum (INT ))); Connect (slider, signal (valuechanged (INT), this, slot (sendmsg (INT ))); } Void cel: fahtocel (INT fahnum) { Int celnum = (fahnum-32) * 5/9; Slider-> setvalue (celnum ); } Void cel: listenchannel () { Qcopchannel * channel = new qcopchannel ("/system/temperature", this); // register a channel Connect (Channel, signal (received (const qstring &, const qbytearray &)), This, slot (handlemsg (const qstring &, const qbytearray &))); } Void cel: handlemsg (const qstring & message, const qbytearray & Data) // process received information { Qdatastream in (data ); If (Message = "convertfahtocel (INT )") { Int fahnum; In> fahnum; Fahtocel (fahnum ); } } Void cel: sendmsg (INT celnum) // Send information { Qbytearray data; Qdatastream out (& Data, qiodevice: writeonly ); Out <celnum; Qcopchannel: Send ("/system/temperature", "convertceltofah (INT)", data ); } # Include <qapplication> # Include "cel. H" Int main (INT argc, char * argv []) { Qapplication app (argc, argv/*, qapplication: guiclient */); Cel screen; Screen. setgeometry (0, 25,100,250 ); Screen. Show (); Return app.exe C (); }

 

// Header file of Fah. h subroutine 2 # Ifndef fah_h # Define fah_h # Include <qwidget> Class qdial; Class qvboxlayout; Class Fah: Public qwidget { Q_object Public: Fah (); ~ Fah (){}; Private slots: Void handlemsg (const qstring & message, const qbytearray & data ); Void sendmsg (INT fahnum ); // Custom slot PRIVATE: Void celtofah (INT celnum ); Void createscreen (); Void createfah (); Void listenchannel (); Qdial * dial; Qvboxlayout * fahlayout; }; # Endif // fah_h # Include <qpushbutton> # Include <qdial> # Include <qlcdnumber> # Include <qvboxlayout> # Include <qapplication> # Include <qcopchannel> # Include <qdatastream> # Include <qbytearray> # Include "Fah. H" Fah: Fah (): qwidget () { Createscreen (); Listenchannel (); } Void Fah: createscreen () { Qpushbutton * quitbtn = new qpushbutton ("quit "); Createfah (); Qvboxlayout * mainlayout = new qvboxlayout; Mainlayout-> addwidget (quitbtn ); Mainlayout-> addlayout (fahlayout ); Setlayout (mainlayout ); Dial-> setfocus (); Connect (quitbtn, signal (clicked (), qapp, slot (quit ())); Setwindowtitle ("Fahrenheit "); } Void Fah: createfah () { Qlcdnumber * lcdnum = new qlcdnumber (3 ); Lcdnum-> setsegmentstyle (qlcdnumber: filled ); Lcdnum-> display (32 ); Dial = new qdial; Dial-> setrange (32,212 ); Dial-> setvalue (32 ); Dial-> setnotchesvisible (true ); Fahlayout = new qvboxlayout; Fahlayout-> addwidget (lcdnum, 0, QT: alignbottom | QT: alignhcenter ); Fahlayout-> addwidget (Dial ); Fahlayout-> setspacing (10 ); Connect (DIAL, signal (valuechanged (INT), lcdnum, slot (Display (INT ))); Connect (DIAL, signal (valuechanged (INT), this, slot (sendmsg (INT ))); } Void Fah: celtofah (INT celnum) { Int fahnum = (celnum * 9/5) + 32; Dial-> setvalue (fahnum ); } Void Fah: listenchannel () { Qcopchannel * channel = new qcopchannel ("/system/temperature", this ); Connect (Channel, signal (received (const qstring &, const qbytearray &)), This, slot (handlemsg (const qstring &, const qbytearray &))); } Void Fah: handlemsg (const qstring & message, const qbytearray & Data) { Qdatastream in (data ); If (Message = "convertceltofah (INT )") { Int celnum; In> celnum; Celtofah (celnum ); } } Void Fah: sendmsg (INT fahnum) { Qbytearray data; Qdatastream out (& Data, qiodevice: writeonly ); Out <fahnum; Qcopchannel: Send ("/system/temperature", "convertfahtocel (INT)", data ); } # Include <qapplication> # Include "Fah. H" Int main (INT argc, char * argv []) { Qapplication app (argc, argv ); Fah screen; Screen. setgeometry( 130, 25,100,250 ); Screen. Show (); Return app.exe C (); }