New option: --pid=PID.

(pid): New global.
(long_options): Add `pid'.
(usage): Describe it.
(tail_forever): Implement it.
(parse_options): Handle the new option and required arg.
Suggestion and pseudo-code from Karl Heuer.

diff --git a/src/tail.c b/src/tail.c
index 771920a4c0485c4bda53a98c386c8ce76036129f..60b7560a7a14bd46863aa4342934416a47581ea9 100644 (file)
--- a/src/tail.c
+++ b/src/tail.c
@@ -172,6 +172,10 @@ char *program_name;
 /* FIXME: allow fractional seconds */
 static unsigned int sleep_interval = 1;
 
+/* The process ID of the process (presumably on the current host)
+   that is writing to all followed files.  */
+static pid_t pid;
+
 /* Nonzero if we have ever read standard input.  */
 static int have_read_stdin;
 
@@ -185,6 +189,7 @@ static struct option const long_options[] =
   {"lines", required_argument, NULL, 'n'},
   {"max-unchanged-stats", required_argument, NULL, CHAR_MAX + 2},
   {"max-consecutive-size-changes", required_argument, NULL, CHAR_MAX + 3},
+  {"pid", required_argument, NULL, CHAR_MAX + 4},
   {"quiet", no_argument, NULL, 'q'},
   {"retry", no_argument, NULL, CHAR_MAX + 1},
   {"silent", no_argument, NULL, 'q'},
@@ -224,6 +229,7 @@ With no FILE, or when FILE is -, read standard input.\n\
                              (the default is %d)\n\
       --max-consecutive-size-changes=N see the texinfo documentation\n\
                              (the default is %d)\n\
+      --pid=PID            with -f, terminate after process ID, PID dies\n\
   -q, --quiet, --silent    never output headers giving file names\n\
   -s, --sleep-interval=S   with -f, sleep S seconds between iterations\n\
   -v, --verbose            always output headers giving file names\n\
@@ -818,6 +824,7 @@ static void
 tail_forever (struct File_spec *f, int nfiles)
 {
   int last;
+  int writer_is_dead = 0;
 
   last = nfiles - 1;
 
@@ -907,7 +914,15 @@ tail_forever (struct File_spec *f, int nfiles)
 
       /* If none of the files changed size, sleep.  */
       if (!any_changed)
-       sleep (sleep_interval);
+       {
+         if (writer_is_dead)
+           break;
+         sleep (sleep_interval);
+
+         /* Once the writer is dead, read the files once more to
+            avoid a race condition.  */
+         writer_is_dead = (kill (pid, 0) != 0);
+       }
     }
 }
 
@@ -1364,6 +1379,19 @@ parse_options (int argc, char **argv,
            }
          break;
 
+       case CHAR_MAX + 4:
+         {
+           strtol_error s_err;
+           unsigned long int tmp_ulong;
+           s_err = xstrtoul (optarg, NULL, 10, &tmp_ulong, "");
+           if (s_err != LONGINT_OK || tmp_ulong > PID_T_MAX)
+             {
+               error (EXIT_FAILURE, 0, _("%s: invalid PID"), optarg);
+             }
+           pid = tmp_ulong;
+         }
+         break;
+
        case 'q':
          *header_mode = never;
          break;