Don't return as fast reading any process output

* src/process.c (wait_reading_process_output):
The patch for Bug#17647 returns too fast sometimes when reading
from any processes. Revert part of it, and limit the timeout more
sensibly (Bug#20978).

1 files changed, 43 insertions, 23 deletions

diff --git a/src/process.c b/src/process.c
index 325c069bd5c..8e046a6dd11 100644
--- a/src/process.c
+++ b/src/process.c
@@ -4585,7 +4585,8 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
   bool no_avail;
   int xerrno;
   Lisp_Object proc;
-  struct timespec timeout, end_time;
+  struct timespec timeout, end_time, timer_delay;
+  struct timespec got_output_end_time = invalid_timespec ();
   enum { MINIMUM = -1, TIMEOUT, INFINITY } wait;
   int got_some_output = -1;
   ptrdiff_t count = SPECPDL_INDEX ();
@@ -4618,7 +4619,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
 
   while (1)
     {
-      bool timeout_reduced_for_timers = false;
+      bool process_skipped = false;
 
       /* If calling from keyboard input, do not quit
          since we want to return C-g as an input character.
@@ -4632,10 +4633,6 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
       if (! NILP (wait_for_cell) && ! NILP (XCAR (wait_for_cell)))
         break;
 
-      /* After reading input, vacuum up any leftovers without waiting.  */
-      if (0 <= got_some_output)
-        wait = MINIMUM;
-
       /* Compute time from now till when time limit is up.  */
       /* Exit if already run out.  */
       if (wait == TIMEOUT)
@@ -4655,8 +4652,6 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
       if (NILP (wait_for_cell)
           && just_wait_proc >= 0)
         {
-          struct timespec timer_delay;
-
           do
             {
               unsigned old_timers_run = timers_run;
@@ -4687,19 +4682,9 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
               && requeued_events_pending_p ())
             break;
 
-          if (timespec_valid_p (timer_delay))
-            {
-              if (timespec_cmp (timer_delay, timeout) < 0)
-                {
-                  timeout = timer_delay;
-                  timeout_reduced_for_timers = true;
-                }
-            }
-          else
-            {
-              /* This is so a breakpoint can be put here.  */
+          /* This is so a breakpoint can be put here.  */
+          if (!timespec_valid_p (timer_delay))
               wait_reading_process_output_1 ();
-            }
         }
 
       /* Cause C-g and alarm signals to take immediate action,
@@ -4869,6 +4854,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                       if (!XPROCESS (proc)->read_output_skip)
                         continue;
                       FD_CLR (channel, &Available);
+                      process_skipped = true;
                       XPROCESS (proc)->read_output_skip = 0;
                       if (XPROCESS (proc)->read_output_delay < adaptive_nsecs)
                         adaptive_nsecs = XPROCESS (proc)->read_output_delay;
@@ -4878,6 +4864,29 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
               process_output_skip = 0;
             }
 
+          /* If we've got some output and haven't limited our timeout
+             with adaptive read buffering, limit it. */
+          if (got_some_output > 0 && !process_skipped
+              && (timeout.tv_sec
+                  || timeout.tv_nsec > READ_OUTPUT_DELAY_INCREMENT))
+            timeout = make_timespec (0, READ_OUTPUT_DELAY_INCREMENT);
+
+
+          if (NILP (wait_for_cell) && just_wait_proc >= 0
+              && timespec_valid_p (timer_delay)
+              && timespec_cmp (timer_delay, timeout) < 0)
+            {
+              struct timespec timeout_abs = timespec_add (current_timespec (),
+                                                          timeout);
+              if (!timespec_valid_p (got_output_end_time)
+                  || timespec_cmp (timeout_abs,
+                                   got_output_end_time) < 0)
+                got_output_end_time = timeout_abs;
+              timeout = timer_delay;
+            }
+          else
+            got_output_end_time = invalid_timespec ();
+
 #if defined (HAVE_NS)
           nfds = ns_select
 #elif defined (HAVE_GLIB)
@@ -4949,9 +4958,17 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
       /*  If we woke up due to SIGWINCH, actually change size now.  */
       do_pending_window_change (0);
 
-      if (wait < INFINITY && nfds == 0 && ! timeout_reduced_for_timers)
-        /* We waited the full specified time, so return now.  */
-        break;
+      if (nfds == 0)
+        {
+          struct timespec now = current_timespec ();
+          if ((timeout.tv_sec == 0 && timeout.tv_nsec == 0)
+              || (wait == TIMEOUT && timespec_cmp (end_time, now) <= 0)
+              || (!process_skipped && got_some_output > 0
+                  && (!timespec_valid_p (got_output_end_time)
+                      || timespec_cmp (got_output_end_time, now) <= 0)))
+            break;
+        }
+
       if (nfds < 0)
         {
           if (xerrno == EINTR)
@@ -5079,6 +5096,9 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                 got_some_output = nread;
               if (nread > 0)
                 {
+                  /* Vacuum up any leftovers without waiting.  */
+                  if (wait_proc == XPROCESS (proc))
+                    wait = MINIMUM;
                   /* Since read_process_output can run a filter,
                      which can call accept-process-output,
                      don't try to read from any other processes