How can I get to know, in the reader process, if the write end of pipe is still active (writer process didn't close its descriptor or exit). I mean Posix (C language) interface. As it seems, if the reader process has is descriptor NONBLOCK, it cannot be guessed by the effect of "read" call. I tried checking the desciptor flags but they don't change:
Writer:
#include <unistd.h>
int main() {
sleep(2);
//actually doesn't write anything but has
//stdout open and exits before reader does
}
Reader:
#include <fcntl.h>
#include <cstdio>
#include <unistd.h>
int main() {
int i = fcntl(0, F_GETFL);
int j = fcntl(0, F_GETFD);
//now the write end is alive
printf("i: %d, j: %d\n", i, j);
sleep(3);
i = fcntl(0, F_GETFL);
j = fcntl(0, F_GETFD);
//now the write end has exited
printf("i: %d, j: %d\n", i, j);
//all flags are all the time 0
}
Supposing that these programs were connected into a pipeline (using "pipe" call) by some external program.
read will return 0 once the write end of the pipe is closed and all pending data is read. If there is no data and the pipe is not closed and non-blocking mode is enabled read will return -1 and set errno to EAGAIN.
When the write end is closed poll will return a POLLHUP event for the pipe.