If I have two instances of Glib::IOChannel, they block until both written. What is the correct way to do this? - gtk

Question

I have modified the example found here to use two io channels. None of the callbacks seem to be called before I have written to both channels. After that they are called individually when writing to the fifos. Am I forgetting something?
Start the test program in one shell window.
Write echo "abc" > testfifo1 in second shell window. -> nothing happens.
Write echo "def" > testfifo2 in a third shell window. -> now I get "abc" and "def"
Write to one of the fifos. This is immediately served.
Edit:
The solution, as hinted by Gormley below, was the lack of nonblock.
read_fd1 = open("testfifo1", O_RDONLY | O_NONBLOCK);
...
read_fd2 = open("testfifo2", O_RDONLY | O_NONBLOCK);
This change to the code below made it respond immediately.
The code:
#include <gtkmm/main.h>
#include <fcntl.h>
#include <iostream>
int read_fd1, read_fd2;
Glib::RefPtr<Glib::IOChannel> iochannel1, iochannel2;
// Usage: "echo "Hello" > testfifo<1|2>", quit with "Q"
bool MyCallback1(Glib::IOCondition io_condition)
{
Glib::ustring buf;
iochannel1->read_line(buf);
std::cout << "io 1: " << buf;
if (buf == "Q\n")
Gtk::Main::quit();
return true;
}
bool MyCallback2(Glib::IOCondition io_condition)
{
Glib::ustring buf;
iochannel2->read_line(buf);
std::cout << "io 2: " << buf;
if (buf == "Q\n")
Gtk::Main::quit();
return true;
}
int main(int argc, char *argv[])
{
// the usual Gtk::Main object
Gtk::Main app(argc, argv);
if (access("testfifo1", F_OK) == -1)
{
if (mkfifo("testfifo1", 0666) != 0)
return -1;
}
if (access("testfifo2", F_OK) == -1)
{
if (mkfifo("testfifo2", 0666) != 0)
return -1;
}
read_fd1 = open("testfifo1", O_RDONLY);
if (read_fd1 == -1)
return -1;
read_fd2 = open("testfifo2", O_RDONLY);
if (read_fd2 == -1)
return -1;
Glib::signal_io().connect(sigc::ptr_fun(MyCallback1), read_fd1, Glib::IO_IN);
Glib::signal_io().connect(sigc::ptr_fun(MyCallback2), read_fd2, Glib::IO_IN);
iochannel1 = Glib::IOChannel::create_from_fd(read_fd1);
iochannel2 = Glib::IOChannel::create_from_fd(read_fd2);
app.run();
if (unlink("testfifo1"))
std::cerr << "error removing fifo 1" << std::endl;
if (unlink("testfifo2"))
std::cerr << "error removing fifo 2" << std::endl;
return 0;
}

Answer 1

These two statements block the program from getting into the main loop until both fifos
are open for write. fifos block until both sides are connected
iochannel1 = Glib::IOChannel::create_from_fd(read_fd1);
iochannel2 = Glib::IOChannel::create_from_fd(read_fd2);