Avoid hangs in accept-process-output.

* lisp.h, process.c (wait_reading_process_input):
Return int, not bool.  All uses changed.
* process.c (SELECT_CANT_DO_WRITE_MASK):
Remove macro, replacing with ...
(SELECT_CAN_DO_WRITE_MASK): ... new constant, with inverted sense.
All uses changed.
(status_notify): New arg WAIT_PROC.  Return int, not void.
All uses changed.

Fixes: debbugs:17647

1 files changed, 64 insertions, 58 deletions

diff --git a/src/process.c b/src/process.c
index 5006c85fe9d..592c43acc2d 100644
--- a/src/process.c
+++ b/src/process.c
@@ -224,8 +224,9 @@ static EMACS_INT update_tick;
 /* Only W32 has this, it really means that select can't take write mask.  */
 #ifdef BROKEN_NON_BLOCKING_CONNECT
 #undef NON_BLOCKING_CONNECT
-#define SELECT_CANT_DO_WRITE_MASK
+enum { SELECT_CAN_DO_WRITE_MASK = false };
 #else
+enum { SELECT_CAN_DO_WRITE_MASK = true };
 #ifndef NON_BLOCKING_CONNECT
 #ifdef HAVE_SELECT
 #if defined (HAVE_GETPEERNAME) || defined (GNU_LINUX)
@@ -281,7 +282,7 @@ static void create_process (Lisp_Object, char **, Lisp_Object);
 static bool keyboard_bit_set (fd_set *);
 #endif
 static void deactivate_process (Lisp_Object);
-static void status_notify (struct Lisp_Process *);
+static int status_notify (struct Lisp_Process *, struct Lisp_Process *);
 static int read_process_output (Lisp_Object, int);
 static void handle_child_signal (int);
 static void create_pty (Lisp_Object);
@@ -860,7 +861,7 @@ nil, indicating the current buffer's process.  */)
     {
       pset_status (p, list2 (Qexit, make_number (0)));
       p->tick = ++process_tick;
-      status_notify (p);
+      status_notify (p, NULL);
       redisplay_preserve_echo_area (13);
     }
   else
@@ -880,7 +881,7 @@ nil, indicating the current buffer's process.  */)
             pset_status (p, list2 (Qsignal, make_number (SIGKILL)));
 
           p->tick = ++process_tick;
-          status_notify (p);
+          status_notify (p, NULL);
           redisplay_preserve_echo_area (13);
         }
     }
@@ -3986,12 +3987,13 @@ is nil, from any process) before the timeout expired.  */)
     nsecs = 0;
 
   return
-    (wait_reading_process_output (secs, nsecs, 0, 0,
+    ((wait_reading_process_output (secs, nsecs, 0, 0,
                                   Qnil,
                                   !NILP (process) ? XPROCESS (process) : NULL,
                                   NILP (just_this_one) ? 0 :
                                   !INTEGERP (just_this_one) ? 1 : -1)
-     ? Qt : Qnil);
+      <= 0)
+     ? Qnil : Qt);
 }
 
 /* Accept a connection for server process SERVER on CHANNEL.  */
@@ -4262,10 +4264,11 @@ wait_reading_process_output_1 (void)
      (suspending output from other processes).  A negative value
      means don't run any timers either.
 
-   Return true if we received input from WAIT_PROC, or from any
-   process if WAIT_PROC is null.  */
+   Return positive if we received input from WAIT_PROC (or from any
+   process if WAIT_PROC is null), zero if we attempted to receive
+   input but got none, and negative if we didn't even try.  */
 
-bool
+int
 wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                              bool do_display,
                              Lisp_Object wait_for_cell,
@@ -4280,8 +4283,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
   int xerrno;
   Lisp_Object proc;
   struct timespec timeout, end_time;
-  int wait_channel = -1;
-  bool got_some_input = 0;
+  int got_some_input = -1;
   ptrdiff_t count = SPECPDL_INDEX ();
 
   FD_ZERO (&Available);
@@ -4292,10 +4294,6 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
            && EQ (XCAR (wait_proc->status), Qexit)))
     message1 ("Blocking call to accept-process-output with quit inhibited!!");
 
-  /* If wait_proc is a process to watch, set wait_channel accordingly.  */
-  if (wait_proc != NULL)
-    wait_channel = wait_proc->infd;
-
   record_unwind_protect_int (wait_reading_process_output_unwind,
                              waiting_for_user_input_p);
   waiting_for_user_input_p = read_kbd;
@@ -4332,6 +4330,10 @@ 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_input)
+        nsecs = -1;
+
       /* Compute time from now till when time limit is up.  */
       /* Exit if already run out.  */
       if (nsecs < 0)
@@ -4450,7 +4452,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
               /* It's okay for us to do this and then continue with
                  the loop, since timeout has already been zeroed out.  */
               clear_waiting_for_input ();
-              status_notify (NULL);
+              got_some_input = status_notify (NULL, wait_proc);
               if (do_display) redisplay_preserve_echo_area (13);
             }
         }
@@ -4472,18 +4474,23 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
           while (wait_proc->infd >= 0)
             {
               int nread = read_process_output (proc, wait_proc->infd);
-
-              if (nread == 0)
-                break;
-
-              if (nread > 0)
-                got_some_input = read_some_bytes = 1;
-              else if (nread == -1 && (errno == EIO || errno == EAGAIN))
-                break;
+              if (nread < 0)
+                {
+                  if (errno == EIO || errno == EAGAIN)
+                    break;
 #ifdef EWOULDBLOCK
-              else if (nread == -1 && EWOULDBLOCK == errno)
-                break;
+                  if (errno == EWOULDBLOCK)
+                    break;
 #endif
+                }
+              else
+                {
+                  if (got_some_input < nread)
+                    got_some_input = nread;
+                  if (nread == 0)
+                    break;
+                  read_some_bytes = true;
+                }
             }
           if (read_some_bytes && do_display)
             redisplay_preserve_echo_area (10);
@@ -4514,12 +4521,8 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
           else
             Available = input_wait_mask;
           Writeok = write_mask;
-#ifdef SELECT_CANT_DO_WRITE_MASK
-          check_write = 0;
-#else
-          check_write = 1;
-#endif
-          check_delay = wait_channel >= 0 ? 0 : process_output_delay_count;
+          check_delay = wait_proc ? 0 : process_output_delay_count;
+          check_write = SELECT_CAN_DO_WRITE_MASK;
         }
 
       /* If frame size has changed or the window is newly mapped,
@@ -4545,6 +4548,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
         {
           nfds = read_kbd ? 0 : 1;
           no_avail = 1;
+          FD_ZERO (&Available);
         }
 
       if (!no_avail)
@@ -4554,7 +4558,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
           /* Set the timeout for adaptive read buffering if any
              process has non-zero read_output_skip and non-zero
              read_output_delay, and we are not reading output for a
-             specific wait_channel.  It is not executed if
+             specific process.  It is not executed if
              Vprocess_adaptive_read_buffering is nil.  */
           if (process_output_skip && check_delay > 0)
             {
@@ -4667,12 +4671,6 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
             report_file_errno ("Failed select", Qnil, xerrno);
         }
 
-      if (no_avail)
-        {
-          FD_ZERO (&Available);
-          check_write = 0;
-        }
-
       /* Check for keyboard input */
       /* If there is any, return immediately
          to give it higher priority than subprocesses */
@@ -4739,9 +4737,6 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
         handle_input_available_signal (SIGIO);
 #endif
 
-      if (! wait_proc)
-        got_some_input |= nfds > 0;
-
       /* If checking input just got us a size-change event from X,
          obey it now if we should.  */
       if (read_kbd || ! NILP (wait_for_cell))
@@ -4773,12 +4768,6 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
               /* If waiting for this channel, arrange to return as
                  soon as no more input to be processed.  No more
                  waiting.  */
-              if (wait_channel == channel)
-                {
-                  wait_channel = -1;
-                  nsecs = -1;
-                  got_some_input = 1;
-                }
               proc = chan_process[channel];
               if (NILP (proc))
                 continue;
@@ -4794,6 +4783,8 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                  buffered-ahead character if we have one.  */
 
               nread = read_process_output (proc, channel);
+              if ((!wait_proc || wait_proc == XPROCESS (proc)) && got_some_input < nread)
+                got_some_input = nread;
               if (nread > 0)
                 {
                   /* Since read_process_output can run a filter,
@@ -5814,7 +5805,7 @@ process_send_signal (Lisp_Object process, int signo, Lisp_Object current_group,
       p->tick = ++process_tick;
       if (!nomsg)
         {
-          status_notify (NULL);
+          status_notify (NULL, NULL);
           redisplay_preserve_echo_area (13);
         }
     }
@@ -6337,14 +6328,20 @@ exec_sentinel (Lisp_Object proc, Lisp_Object reason)
 /* Report all recent events of a change in process status
    (either run the sentinel or output a message).
    This is usually done while Emacs is waiting for keyboard input
-   but can be done at other times.  */
+   but can be done at other times.
 
-static void
-status_notify (struct Lisp_Process *deleting_process)
+   Return positive if any input was received from WAIT_PROC (or from
+   any process if WAIT_PROC is null), zero if input was attempted but
+   none received, and negative if we didn't even try.  */
+
+static int
+status_notify (struct Lisp_Process *deleting_process,
+               struct Lisp_Process *wait_proc)
 {
-  register Lisp_Object proc;
+  Lisp_Object proc;
   Lisp_Object tail, msg;
   struct gcpro gcpro1, gcpro2;
+  int got_some_input = -1;
 
   tail = Qnil;
   msg = Qnil;
@@ -6374,8 +6371,14 @@ status_notify (struct Lisp_Process *deleting_process)
                  /* Network or serial process not stopped:  */
                  && ! EQ (p->command, Qt)
                  && p->infd >= 0
-                 && p != deleting_process
-                 && read_process_output (proc, p->infd) > 0);
+                 && p != deleting_process)
+            {
+              int nread = read_process_output (proc, p->infd);
+              if (got_some_input < nread)
+                got_some_input = nread;
+              if (nread <= 0)
+                break;
+            }
 
           /* Get the text to use for the message.  */
           if (p->raw_status_new)
@@ -6407,6 +6410,7 @@ status_notify (struct Lisp_Process *deleting_process)
 
   update_mode_lines = 24;  /* In case buffers use %s in mode-line-format.  */
   UNGCPRO;
+  return got_some_input;
 }
 
 DEFUN ("internal-default-process-sentinel", Finternal_default_process_sentinel,
@@ -6618,9 +6622,11 @@ extern int sys_select (int, fd_set *, fd_set *, fd_set *,
    DO_DISPLAY means redisplay should be done to show subprocess
    output that arrives.
 
-   Return true if we received input from any process.  */
+   Return positive if we received input from WAIT_PROC (or from any
+   process if WAIT_PROC is null), zero if we attempted to receive
+   input but got none, and negative if we didn't even try.  */
 
-bool
+int
 wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
                              bool do_display,
                              Lisp_Object wait_for_cell,
@@ -6808,7 +6814,7 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
 
   start_polling ();
 
-  return 0;
+  return -1;
 }
 
 #endif  /* not subprocesses */