bug#17805: 24.3.50; Crash in -[EmacsApp / Faccept_process_output

[Paul Eggert <eggert@cs.ucla.edu>]

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Thanks for the bug report.  Is the bug reproducible?  Does the attached 
patch fix it?  Sorry, I don't use OS X, so I can't easily test this fix.

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=== modified file 'src/ChangeLog'
--- src/ChangeLog	2014-06-18 19:17:23 +0000
+++ src/ChangeLog	2014-06-18 21:32:40 +0000
@@ -1,3 +1,16 @@
+2014-06-18  Paul Eggert  <eggert@cs.ucla.edu>
+
+	Avoid hangs in accept-process-output (Bug#17647, Bug#17805).
+	This fix is backported from the trunk.
+	* 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.
+
 2014-06-18  Eli Zaretskii  <eliz@gnu.org>
 
 	* image.c [5 < GIFLIB_MAJOR + (1 <= GIFLIB_MINOR)]: Declare the

=== modified file 'src/lisp.h'
--- src/lisp.h	2014-06-01 07:06:28 +0000
+++ src/lisp.h	2014-06-18 21:26:42 +0000
@@ -4187,10 +4187,8 @@
 /* Defined in process.c.  */
 extern Lisp_Object QCtype, Qlocal;
 extern void kill_buffer_processes (Lisp_Object);
-extern bool wait_reading_process_output (intmax_t, int, int, bool,
-					 Lisp_Object,
-					 struct Lisp_Process *,
-					 int);
+extern int wait_reading_process_output (intmax_t, int, int, bool, Lisp_Object,
+					struct Lisp_Process *, int);
 /* Max value for the first argument of wait_reading_process_output.  */
 #if __GNUC__ == 3 || (__GNUC__ == 4 && __GNUC_MINOR__ <= 5)
 /* Work around a bug in GCC 3.4.2, known to be fixed in GCC 4.6.3.

=== modified file 'src/process.c'
--- src/process.c	2014-05-03 20:13:10 +0000
+++ src/process.c	2014-06-18 21:27:30 +0000
@@ -224,8 +224,9 @@
 /* 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 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);
@@ -870,7 +871,7 @@
     {
       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
@@ -890,7 +891,7 @@
 	    pset_status (p, list2 (Qsignal, make_number (SIGKILL)));
 
 	  p->tick = ++process_tick;
-	  status_notify (p);
+	  status_notify (p, NULL);
 	  redisplay_preserve_echo_area (13);
 	}
     }
@@ -3997,12 +3998,13 @@
     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.  */
@@ -4274,11 +4276,10 @@
      (suspending output from other processes).  A negative value
      means don't run any timers either.
 
-   If WAIT_PROC is specified, then the function returns true if we
-     received input from that process before the timeout elapsed.
-   Otherwise, return true if we received input from any process.  */
+   Return true if we received input from WAIT_PROC, or from any
+   process if WAIT_PROC is null.  */
 
-bool
+int
 wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
 			     bool do_display,
 			     Lisp_Object wait_for_cell,
@@ -4293,8 +4294,7 @@
   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);
@@ -4305,10 +4305,6 @@
 	   && 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;
@@ -4345,6 +4341,10 @@
       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)
@@ -4463,7 +4463,7 @@
 	      /* 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);
 	    }
 	}
@@ -4485,18 +4485,23 @@
 	  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);
@@ -4527,12 +4532,8 @@
 	  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,
@@ -4558,6 +4559,7 @@
 	{
 	  nfds = read_kbd ? 0 : 1;
 	  no_avail = 1;
+	  FD_ZERO (&Available);
 	}
 
       if (!no_avail)
@@ -4567,7 +4569,7 @@
 	  /* 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)
 	    {
@@ -4679,12 +4681,6 @@
 	    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 */
@@ -4751,9 +4747,6 @@
 	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))
@@ -4785,12 +4778,6 @@
 	      /* 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;
@@ -4806,6 +4793,8 @@
 		 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,
@@ -5826,7 +5815,7 @@
       p->tick = ++process_tick;
       if (!nomsg)
 	{
-	  status_notify (NULL);
+	  status_notify (NULL, NULL);
 	  redisplay_preserve_echo_area (13);
 	}
     }
@@ -6354,14 +6343,20 @@
 /* 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.  */
-
-static void
-status_notify (struct Lisp_Process *deleting_process)
+   but can be done at other times.
+
+   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;
@@ -6391,8 +6386,14 @@
 		 /* 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)
@@ -6424,6 +6425,7 @@
 
   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,
@@ -6635,9 +6637,11 @@
    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,
@@ -6825,7 +6829,7 @@
 
   start_polling ();
 
-  return 0;
+  return -1;
 }
 
 #endif	/* not subprocesses */