How to get an X11 Window from a Process ID ?
- by Adam Pierce
Under Linux, my C++ application is using fork() and execv() to launch multiple instances of OpenOffice so as to view some powerpoint slide shows. This part works.
Next I want to be able to move the OpenOffice windows to specific locations on the display. I can do that with the XMoveResizeWindow() function but I need to find the Window for each instance.
I have the process ID of each instance, how can I find the X11 Window from that ?
UPDATE - Thanks to Andy's suggestion, I have pulled this off. I'm posting the code here to share it with the Stack Overflow community.
Unfortunately Open Office does not seem to set the _NET_WM_PID property so this doesn't ultimately solve my problem but it does answer the question.
// Attempt to identify a window by name or attribute.
// by Adam Pierce <[email protected]>
#include <X11/Xlib.h>
#include <X11/Xatom.h>
#include <iostream>
#include <list>
using namespace std;
class WindowsMatchingPid
{
public:
WindowsMatchingPid(Display *display, Window wRoot, unsigned long pid)
: _display(display)
, _pid(pid)
{
// Get the PID property atom.
_atomPID = XInternAtom(display, "_NET_WM_PID", True);
if(_atomPID == None)
{
cout << "No such atom" << endl;
return;
}
search(wRoot);
}
const list<Window> &result() const { return _result; }
private:
unsigned long _pid;
Atom _atomPID;
Display *_display;
list<Window> _result;
void search(Window w)
{
// Get the PID for the current Window.
Atom type;
int format;
unsigned long nItems;
unsigned long bytesAfter;
unsigned char *propPID = 0;
if(Success == XGetWindowProperty(_display, w, _atomPID, 0, 1, False, XA_CARDINAL,
&type, &format, &nItems, &bytesAfter, &propPID))
{
if(propPID != 0)
{
// If the PID matches, add this window to the result set.
if(_pid == *((unsigned long *)propPID))
_result.push_back(w);
XFree(propPID);
}
}
// Recurse into child windows.
Window wRoot;
Window wParent;
Window *wChild;
unsigned nChildren;
if(0 != XQueryTree(_display, w, &wRoot, &wParent, &wChild, &nChildren))
{
for(unsigned i = 0; i < nChildren; i++)
search(wChild[i]);
}
}
};
int main(int argc, char **argv)
{
if(argc < 2)
return 1;
int pid = atoi(argv[1]);
cout << "Searching for windows associated with PID " << pid << endl;
// Start with the root window.
Display *display = XOpenDisplay(0);
WindowsMatchingPid match(display, XDefaultRootWindow(display), pid);
// Print the result.
const list<Window> &result = match.result();
for(list<Window>::const_iterator it = result.begin(); it != result.end(); it++)
cout << "Window #" << (unsigned long)(*it) << endl;
return 0;
}
