Re: [pstreams-users] Empty process output

[Jonathan W. <pst...@ka...>]

On 6 February 2013 13:39, Johannes Wienke wrote:
>
> Actually the process I am inspecting is still alive, but there seems to
> be a bug in pstree when a thread of that process goes away. In that case
> pstree tries to access the thread's stat-file and exists with "No such
> file or directory" on stderr. Not exactly what I expected from such a
> tool... I will search for a different way to find all subprocesses.

Eurgh, that's not very helpful either.

I suppose you could read from the child process' stderr and if you get
that error then you could try calling pstree again, e.g. (untested)

#include <pstreams/pstream.h>
#include <sstream>
#include <iostream>

int main(int argc, char** argv)
{
    std::string pid = argc > 1 ? argv[1] : "1";
    std::string pstreeOut;
    while (pstreeOut.empty())
    {
        redi::ipstream in("pstree -pa " + pid);
        std::stringstream ss;
        ss << in.rdbuf();
        pstreeOut = ss.str();

        if (pstreeOut.empty()) {
            ss << in.err().rdbuf();
            pstreeOut = ss.str();
            // handle pstree error when a thread terminates while processing
            if (pstreeOut.find("No such file or directory") ==
std::string::npos)
                throw std::runtime_error("No such process: " + pid);
        }
    }
    std::cout << pstreeOut << '\n';
}