XLib Disconnection Callback

I use XLib and XRand to get some information about the connected displays on an embedded system.

class Foo {

private:

    Display *_display{};



public:

    Foo() {

        _display = XOpenDisplay(":0.0");

    }



    void getSomeInfo() const {

        /* Get some info with _display */

    }



    ~Foo() {

        XCloseDisplay(_display);

    }

}

The problem is, X server can be shut down (for low power or some other purposes) after the creation of Foo instance and before calling getSomeInfo(), which causes immediate death of my application because XLib tries to exit application in case of errors.

Is there any mechanism, like a callback, which would allow me to understand that X Server went down and I should not use the _display pointer anymore ?

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

Does "use XCB instead of Xlib" count as an answer? If so, I can provide that as an answer. XCB never calls exit for you and it actually provides some error status codes.

– Uli Schlachter
Nov 29 '18 at 16:24

add a comment |

I use XLib and XRand to get some information about the connected displays on an embedded system.

class Foo {

private:

    Display *_display{};



public:

    Foo() {

        _display = XOpenDisplay(":0.0");

    }



    void getSomeInfo() const {

        /* Get some info with _display */

    }



    ~Foo() {

        XCloseDisplay(_display);

    }

}

Is there any mechanism, like a callback, which would allow me to understand that X Server went down and I should not use the _display pointer anymore ?

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

Does "use XCB instead of Xlib" count as an answer? If so, I can provide that as an answer. XCB never calls exit for you and it actually provides some error status codes.

– Uli Schlachter
Nov 29 '18 at 16:24

add a comment |

I use XLib and XRand to get some information about the connected displays on an embedded system.

class Foo {

private:

    Display *_display{};



public:

    Foo() {

        _display = XOpenDisplay(":0.0");

    }



    void getSomeInfo() const {

        /* Get some info with _display */

    }



    ~Foo() {

        XCloseDisplay(_display);

    }

}

Is there any mechanism, like a callback, which would allow me to understand that X Server went down and I should not use the _display pointer anymore ?

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

I use XLib and XRand to get some information about the connected displays on an embedded system.

class Foo {

private:

    Display *_display{};



public:

    Foo() {

        _display = XOpenDisplay(":0.0");

    }



    void getSomeInfo() const {

        /* Get some info with _display */

    }



    ~Foo() {

        XCloseDisplay(_display);

    }

}

Is there any mechanism, like a callback, which would allow me to understand that X Server went down and I should not use the _display pointer anymore ?

xlib xrandr

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

asked Nov 20 '18 at 16:02

Murat Şeker

1,1751921

Does "use XCB instead of Xlib" count as an answer? If so, I can provide that as an answer. XCB never calls exit for you and it actually provides some error status codes.

– Uli Schlachter
Nov 29 '18 at 16:24

add a comment |

Does "use XCB instead of Xlib" count as an answer? If so, I can provide that as an answer. XCB never calls exit for you and it actually provides some error status codes.

– Uli Schlachter
Nov 29 '18 at 16:24

Does "use XCB instead of Xlib" count as an answer? If so, I can provide that as an answer. XCB never calls exit for you and it actually provides some error status codes.

– Uli Schlachter
Nov 29 '18 at 16:24

add a comment |

1 Answer
1

active

oldest

votes

I fear that your only option is to use XSetIOErrorHandler and then do something ugly.

From https://tronche.com/gui/x/xlib/event-handling/protocol-errors/XSetIOErrorHandler.html:

The XSetIOErrorHandler() sets the fatal I/O error handler. Xlib calls the program's supplied error handler if any sort of system call error occurs (for example, the connection to the server was lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O error handler does return, the client process exits.

The "do something ugly" that I would suggest is to use setjmp and longjmp: Whenever you call any Xlib functions, you setjmp before. Your I/O error handling function then longjmps away to get away from the I/O error without your process exiting.

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

I have to say that I'm impressed :) but this kind of tricks are not allowed on our codebase.

– Murat Şeker
Dec 3 '18 at 10:02

Good for you that such hacks are not allowed. Bad for you that then your only option is Xlib, I guess. (You are not allowed to interpose libc's exit() to replace it with your own no-op function, right? ;-) )

– Uli Schlachter
Dec 3 '18 at 11:04

add a comment |

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1 Answer
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active

oldest

votes

1 Answer
1

active

oldest

votes

I fear that your only option is to use XSetIOErrorHandler and then do something ugly.

From https://tronche.com/gui/x/xlib/event-handling/protocol-errors/XSetIOErrorHandler.html:

The XSetIOErrorHandler() sets the fatal I/O error handler. Xlib calls the program's supplied error handler if any sort of system call error occurs (for example, the connection to the server was lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O error handler does return, the client process exits.

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

I have to say that I'm impressed :) but this kind of tricks are not allowed on our codebase.

– Murat Şeker
Dec 3 '18 at 10:02

Good for you that such hacks are not allowed. Bad for you that then your only option is Xlib, I guess. (You are not allowed to interpose libc's exit() to replace it with your own no-op function, right? ;-) )

– Uli Schlachter
Dec 3 '18 at 11:04

add a comment |

I fear that your only option is to use XSetIOErrorHandler and then do something ugly.

From https://tronche.com/gui/x/xlib/event-handling/protocol-errors/XSetIOErrorHandler.html:

The XSetIOErrorHandler() sets the fatal I/O error handler. Xlib calls the program's supplied error handler if any sort of system call error occurs (for example, the connection to the server was lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O error handler does return, the client process exits.

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

I have to say that I'm impressed :) but this kind of tricks are not allowed on our codebase.

– Murat Şeker
Dec 3 '18 at 10:02

Good for you that such hacks are not allowed. Bad for you that then your only option is Xlib, I guess. (You are not allowed to interpose libc's exit() to replace it with your own no-op function, right? ;-) )

– Uli Schlachter
Dec 3 '18 at 11:04

add a comment |

I fear that your only option is to use XSetIOErrorHandler and then do something ugly.

From https://tronche.com/gui/x/xlib/event-handling/protocol-errors/XSetIOErrorHandler.html:

The XSetIOErrorHandler() sets the fatal I/O error handler. Xlib calls the program's supplied error handler if any sort of system call error occurs (for example, the connection to the server was lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O error handler does return, the client process exits.

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

I fear that your only option is to use XSetIOErrorHandler and then do something ugly.

From https://tronche.com/gui/x/xlib/event-handling/protocol-errors/XSetIOErrorHandler.html:

The XSetIOErrorHandler() sets the fatal I/O error handler. Xlib calls the program's supplied error handler if any sort of system call error occurs (for example, the connection to the server was lost). This is assumed to be a fatal condition, and the called routine should not return. If the I/O error handler does return, the client process exits.

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

answered Nov 29 '18 at 16:24

Uli Schlachter

5,0131729

I have to say that I'm impressed :) but this kind of tricks are not allowed on our codebase.

– Murat Şeker
Dec 3 '18 at 10:02

Good for you that such hacks are not allowed. Bad for you that then your only option is Xlib, I guess. (You are not allowed to interpose libc's exit() to replace it with your own no-op function, right? ;-) )

– Uli Schlachter
Dec 3 '18 at 11:04

add a comment |

I have to say that I'm impressed :) but this kind of tricks are not allowed on our codebase.

– Murat Şeker
Dec 3 '18 at 10:02

Good for you that such hacks are not allowed. Bad for you that then your only option is Xlib, I guess. (You are not allowed to interpose libc's exit() to replace it with your own no-op function, right? ;-) )

– Uli Schlachter
Dec 3 '18 at 11:04

I have to say that I'm impressed :) but this kind of tricks are not allowed on our codebase.

– Murat Şeker
Dec 3 '18 at 10:02

Good for you that such hacks are not allowed. Bad for you that then your only option is Xlib, I guess. (You are not allowed to interpose libc's exit() to replace it with your own no-op function, right? ;-) )

– Uli Schlachter
Dec 3 '18 at 11:04

add a comment |

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