less: yet another attempt to make search better

1 files changed, 17 insertions, 1 deletions

diff --git a/miscutils/less.c b/miscutils/less.c
index b0e2754f8..207f5864e 100644
--- a/miscutils/less.c
+++ b/miscutils/less.c
@@ -21,6 +21,8 @@
  *   redirected input has been read from stdin
  */
 
+#include <sched.h>      /* sched_yield() */
+
 #include "busybox.h"
 #if ENABLE_FEATURE_LESS_REGEXP
 #include "xregex.h"
@@ -200,16 +202,30 @@ static void read_lines(void)
                         char c;
                         /* if no unprocessed chars left, eat more */
                         if (readpos >= readeof) {
+                                smallint yielded = 0;
+
                                 ndelay_on(0);
+ read_again:
                                 eof_error = safe_read(0, readbuf, sizeof(readbuf));
-                                ndelay_off(0);
                                 readpos = 0;
                                 readeof = eof_error;
                                 if (eof_error < 0) {
+                                        if (errno == EAGAIN && !yielded) {
+                        /* We can hit EAGAIN while searching for regexp match.
+                         * Yield is not 100% reliable solution in general,
+                         * but for less it should be good enough.
+                         * We give stdin supplier some CPU time to produce more.
+                         * We do it just once. */
+                                                sched_yield();
+                                                yielded = 1;
+                                                goto read_again;
+                                        }
                                         readeof = 0;
                                         if (errno != EAGAIN)
                                                 print_statusline("read error");
                                 }
+                                ndelay_off(0);
+
                                 if (eof_error <= 0) {
                                         goto reached_eof;
                                 }