diff options
| -rw-r--r-- | NEWS | 6 | ||||
| -rw-r--r-- | src/tail.c | 46 | ||||
| -rwxr-xr-x | tests/tail-2/pid | 15 |
3 files changed, 38 insertions, 29 deletions
@@ -22,6 +22,12 @@ GNU coreutils NEWS -*- outline -*- from a failed stat/lstat. For example ls -Lis now prints "?", not "0", for the inode number and allocated size of a dereferenced dangling symlink. + tail --follow --pid now avoids a race condition where data written + just before the process dies might not have been output by tail. + Also, tail no longer delays at all when the specified pid is not live. + [The race was introduced in coreutils-7.5, + and the unnecessary delay was present since textutils-1.22o] + ** Portability On Solaris 9, many commands would mistakenly treat file/ the same as diff --git a/src/tail.c b/src/tail.c index f9f8c3904..f3fe6a341 100644 --- a/src/tail.c +++ b/src/tail.c @@ -1135,9 +1135,6 @@ tail_forever (struct File_spec *f, size_t n_files, double sleep_interval) if (writer_is_dead) break; - if (xnanosleep (sleep_interval)) - error (EXIT_FAILURE, errno, _("cannot read realtime clock")); - /* Once the writer is dead, read the files once more to avoid a race condition. */ writer_is_dead = (pid != 0 @@ -1146,6 +1143,10 @@ tail_forever (struct File_spec *f, size_t n_files, double sleep_interval) signal to the writer, so kill fails and sets errno to EPERM. */ && errno != EPERM); + + if (!writer_is_dead && xnanosleep (sleep_interval)) + error (EXIT_FAILURE, errno, _("cannot read realtime clock")); + } } } @@ -1179,6 +1180,7 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files, Hash_table *wd_table; bool found_watchable = false; + bool writer_is_dead = false; int prev_wd; size_t evlen = 0; char *evbuf; @@ -1266,30 +1268,30 @@ tail_forever_inotify (int wd, struct File_spec *f, size_t n_files, indefinetely. */ if (pid) { - fd_set rfd; - struct timeval select_timeout; - int n_descriptors; - - FD_ZERO (&rfd); - FD_SET (wd, &rfd); + if (writer_is_dead) + exit (EXIT_SUCCESS); - select_timeout.tv_sec = (time_t) sleep_interval; - select_timeout.tv_usec = 1000000 * (sleep_interval - - select_timeout.tv_sec); + writer_is_dead = (kill (pid, 0) != 0 && errno != EPERM); - n_descriptors = select (wd + 1, &rfd, NULL, NULL, &select_timeout); + struct timeval delay; /* how long to wait for file changes. */ + if (writer_is_dead) + delay.tv_sec = delay.tv_usec = 0; + else + { + delay.tv_sec = (time_t) sleep_interval; + delay.tv_usec = 1000000 * (sleep_interval - delay.tv_sec); + } - if (n_descriptors == -1) - error (EXIT_FAILURE, errno, _("error monitoring inotify event")); + fd_set rfd; + FD_ZERO (&rfd); + FD_SET (wd, &rfd); - if (n_descriptors == 0) - { - /* See if the process we are monitoring is still alive. */ - if (kill (pid, 0) != 0 && errno != EPERM) - exit (EXIT_SUCCESS); + int file_change = select (wd + 1, &rfd, NULL, NULL, &delay); - continue; - } + if (file_change == 0) + continue; + else if (file_change == -1) + error (EXIT_FAILURE, errno, _("error monitoring inotify event")); } if (len <= evbuf_off) diff --git a/tests/tail-2/pid b/tests/tail-2/pid index 90f168430..760e289bc 100755 --- a/tests/tail-2/pid +++ b/tests/tail-2/pid @@ -29,26 +29,27 @@ touch here || framework_failure fail=0 for inotify in ---disable-inotify ''; do - # Use tail itself to create a background process to monitor. + # Use tail itself to create a background process to monitor, + # which will auto exit when "here" is removed. tail -f $inotify here & bg_pid=$! # Ensure that tail --pid=PID does not exit when PID is alive. - timeout 1 tail -s.1 -f $inotify here --pid=$bg_pid + timeout 1 tail -f -s.1 --pid=$bg_pid $inotify here test $? = 124 || fail=1 # Cleanup background process kill $bg_pid - # Ensure that tail --pid=PID exits successfully when PID is dead. + # Ensure that tail --pid=PID exits with success status when PID is dead. # Use an unlikely-to-be-live PID - timeout 3 tail -s.1 --pid=$PID_T_MAX -f $inotify /dev/null + timeout 3 tail -f -s.1 --pid=$PID_T_MAX $inotify /dev/null ret=$? - test $ret = 124 && skip_test_ "pid $PID_T_MAX present" + test $ret = 124 && skip_test_ "pid $PID_T_MAX present or tail too slow" test $ret = 0 || fail=1 - # Ensure fractional sleep parameter is honored with --pid - timeout 3 tail -s.1 -f $inotify /dev/null --pid=$PID_T_MAX + # Ensure tail doesn't wait for data when PID is dead + timeout 3 tail -f -s10 --pid=$PID_T_MAX $inotify /dev/null test $? = 124 && fail=1 done |