4 ms·
From the man page: If newfd was open, any errors that would have been reported at close(2) time are lost. A careful programmer will not use dup2() or dup
by FrankBooth 15y ago
From the man page:
If newfd was open, any errors that would have been reported at close(2) time are
lost. A careful programmer will not use dup2() or dup3() without closing newfd
first.
- cperciva 15y agoMaybe your man page says that, but POSIX says The dup2() function may fail if: [EIO] An I/O error occurred while attempting to close fildes2.
- saurik 15y agoWhich is actually "interesting" advice, as it cannot be followed in a multithreaded program without insanely extensive process-wide locks ;P (as any call to open() between close() and dup2() has an irritatingly high probability of grabbing whatever file descriptor you just freed up). (Of course, most usages of dup2() are in contexts just after a fork() or at the beginning of main(), so I guess this could often be practical; it still seems unfortunate.)
- finnw 15y agoMaybe this can still be worked around by copying the target fd first so it can be closed after fdup()ing the source fd, e.g. // Assume x and y are open fds and we want to replace y with a copy of x z = open("/dev/null", O_RDONLY); // Guarantees no other thread is using z dup2(y, z); dup2(x, y); close(z);
- saurik 15y agoHah! (You don't actually need that open("/dev/null") trick, though: you can just use dup(). ;P)