Periodically call sd_journal_process in journalctl

If `journalctl` take a long time to process messages, and during that
time journal file rotation occurs, a `journalctl` client will keep
those rotated files open until it calls `sd_journal_process()`, which
typically happens as a result of calling `sd_journal_wait()` below in
the "following" case.  By periodically calling `sd_journal_process()`
during the processing loop we shrink the window of time a client
instance has open file descriptors for rotated (deleted) journal
files.

**Warning**

This change does not appear to solve the case of a "paused" output
stream. If somebody is using `journalctl | less` and pauses the
output, then without a background thread periodically listening for
inotify delete events and cleaning up, journal logs will eventually
stop flowing in cases where a journal client with enough open files
causes the "free" disk space threshold to be crossed.

1 files changed, 28 insertions, 0 deletions

diff --git a/src/journal/journalctl.c b/src/journal/journalctl.c
index bb9cfb6dc4..2cf35f7e66 100644
--- a/src/journal/journalctl.c
+++ b/src/journal/journalctl.c
@@ -81,6 +81,8 @@
 
 #define DEFAULT_FSS_INTERVAL_USEC (15*USEC_PER_MINUTE)
 
+#define PROCESS_INOTIFY_INTERVAL 1024   /* Every 1,024 messages processed */
+
 #if HAVE_PCRE2
 DEFINE_TRIVIAL_CLEANUP_FUNC(pcre2_match_data*, pcre2_match_data_free);
 DEFINE_TRIVIAL_CLEANUP_FUNC(pcre2_code*, pcre2_code_free);
@@ -2639,6 +2641,32 @@ int main(int argc, char *argv[]) {
                                 goto finish;
 
                         n_shown++;
+                        
+                        /* If journalctl take a long time to process messages, and
+                         * during that time journal file rotation occurs, a journalctl
+                         * client will keep those rotated files open until it calls
+                         * sd_journal_process(), which typically happens as a result
+                         * of calling sd_journal_wait() below in the "following" case.
+                         * By periodically calling sd_journal_process() during the
+                         * processing loop we shrink the window of time a client
+                         * instance has open file descriptors for rotated (deleted)
+                         * journal files.
+                         *
+                         * FIXME: This change does not appear to solve the case of a
+                         * "paused" output stream. If somebody is using `journalctl | less`
+                         * and pauses the output, then without a background thread
+                         * periodically listening for inotify delete events and cleaning
+                         * up, journal logs will eventually stop flowing in cases where
+                         * a journal client with enough open files causes the "free"
+                         * disk space threshold to be crossed. 
+                         */
+                        if ((n_shown % PROCESS_INOTIFY_INTERVAL) == 0) {
+                                r = sd_journal_process(j);
+                                if (r < 0) {
+                                        log_error_errno(r, "Failed to process inotify events: %m");
+                                        goto finish;
+                                }
+                        }
                 }
 
                 if (!arg_follow) {