in_tail: signal pending only once

Prior to this commit, if the tail is watching over multiple files, each
file signals pending and results in calling in_tail_collect_pending()
multiple times. Since function in_tail_collect_pending() goes through
all watched files for pending data so calling it once is sufficient.

This commit changes that by only signal pending event when there is any
pending data from any watched files.

Signed-off-by: Eric Lin <exlin@google.com>

plugins/in_tail/tail_fs_stat.c

@@ -93,6 +93,9 @@ static int tail_fs_check(struct flb_input_instance *ins,
     struct flb_tail_file *file = NULL;
     struct fs_stat *fst;
     struct stat st;
+    int pending_data_detected;
+
+    pending_data_detected = FLB_FALSE;
 
     /* Lookup watched file */
     mk_list_foreach_safe(head, tmp, &ctx->files_event) {
@@ -123,6 +126,9 @@ static int tail_fs_check(struct flb_input_instance *ins,
         if (file->offset > st.st_size) {
             offset = lseek(file->fd, 0, SEEK_SET);
             if (offset == -1) {
+                if (pending_data_detected) {
+                    tail_signal_pending(ctx);
+                }
                 flb_errno();
                 return -1;
             }
@@ -142,7 +148,7 @@ static int tail_fs_check(struct flb_input_instance *ins,
 
         if (file->offset < st.st_size) {
             file->pending_bytes = (st.st_size - file->offset);
-            tail_signal_pending(ctx);
+            pending_data_detected = FLB_TRUE;
         }
         else {
             file->pending_bytes = 0;
@@ -173,6 +179,10 @@ static int tail_fs_check(struct flb_input_instance *ins,
 
     }
 
+    if (pending_data_detected) {
+        tail_signal_pending(ctx);
+    }
+
     return 0;
 }