less: yet another attempt to make search better

diff --git a/miscutils/less.c b/miscutils/less.c
index b0e2754f807c94e9de6b90e7a5c8db0dd9cf6089..207f5864e95bd3832310567e04d7ddb6d2ec8a50 100644 (file)
--- 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;
                                }