Revamp quitting and fix infloops

This fixes some infinite loops that cannot be quitted out of,
e.g., (defun foo () (nth most-positive-fixnum '#1=(1 . #1#)))
when byte-compiled and when run under X.  See:
http://lists.gnu.org/archive/html/emacs-devel/2017-01/msg00577.html
This also attempts to keep the performance improvements I recently
added, as much as possible under the constraint that the infloops
must be caught.  In some cases this fixes infloop bugs recently
introduced when I removed immediate_quit.
* src/alloc.c (Fmake_list):
Use rarely_quit, not maybe_quit, for speed in the usual case.
* src/bytecode.c (exec_byte_code):
* src/editfns.c (Fcompare_buffer_substrings):
* src/fns.c (Fnthcdr):
* src/syntax.c (scan_words, skip_chars, skip_syntaxes)
(Fbackward_prefix_chars):
Use rarely_quit so that users can C-g out of long loops.
* src/callproc.c (call_process_cleanup, call_process):
* src/fileio.c (read_non_regular, Finsert_file_contents):
* src/indent.c (compute_motion):
* src/syntax.c (scan_words, Fforward_comment):
Remove now-unnecessary maybe_quit calls.
* src/callproc.c (call_process):
* src/doc.c (get_doc_string, Fsnarf_documentation):
* src/fileio.c (Fcopy_file, read_non_regular, Finsert_file_contents):
* src/lread.c (safe_to_load_version):
* src/sysdep.c (system_process_attributes) [GNU_LINUX]:
Use emacs_read_quit instead of emacs_read in places where
C-g handling is safe.
* src/eval.c (maybe_quit): Move comment here from lisp.h.
* src/fileio.c (Fcopy_file, e_write):
Use emacs_write_quit instead of emacs_write_sig in places where
C-g handling is safe.
* src/filelock.c (create_lock_file): Use emacs_write, not
plain write, as emacs_write no longer has a problem.
(read_lock_data): Use emacs_read, not read, as emacs_read
no longer has a problem.
* src/fns.c (rarely_quit): Move to lisp.h and rename to
incr_rarely_quit.  All uses changed..
* src/fns.c (Fmemq, Fmemql, Fassq, Frassq, Fplist_put, Fplist_member):
* src/indent.c (compute_motion):
* src/syntax.c (find_defun_start, back_comment, forw_comment)
(Fforward_comment, scan_lists, scan_sexps_forward):
Use incr_rarely_quit so that users can C-g out of long loops.
* src/fns.c (Fnconc): Move incr_rarely_quit call to within
inner loop, so that it catches C-g there too.
* src/keyboard.c (tty_read_avail_input): Remove commented-out
and now-obsolete code dealing with interrupts.
* src/lisp.h (rarely_quit, incr_rarely_quit): New functions,
the latter moved here from fns.c and renamed from rarely_quit.
(emacs_read_quit, emacs_write_quit): New decls.
* src/search.c (find_newline, search_buffer, find_newline1):
Add maybe_quit to catch C-g.
* src/sysdep.c (get_child_status): Always invoke maybe_quit
if interruptible, so that the caller need not bother.
(emacs_nointr_read, emacs_read_quit, emacs_write_quit):
New functions.
(emacs_read): Rewrite in terms of emacs_nointr_read.
Do not handle C-g or signals; that is now for emacs_read_quit.
(emacs_full_write): Replace PROCESS_SIGNALS two-way arg
with INTERRUPTIBLE three-way arg.  All uses changed.

1 files changed, 15 insertions, 33 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index 317669d6a1a..a86e7c5f8e4 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -7041,40 +7041,22 @@ tty_read_avail_input (struct terminal *terminal,
 
   /* Now read; for one reason or another, this will not block.
      NREAD is set to the number of chars read.  */
-  do
-    {
-      nread = emacs_read (fileno (tty->input), (char *) cbuf, n_to_read);
-      /* POSIX infers that processes which are not in the session leader's
-         process group won't get SIGHUPs at logout time.  BSDI adheres to
-         this part standard and returns -1 from read (0) with errno==EIO
-         when the control tty is taken away.
-         Jeffrey Honig <jch@bsdi.com> says this is generally safe.  */
-      if (nread == -1 && errno == EIO)
-        return -2;          /* Close this terminal.  */
-#if defined (AIX) && defined (_BSD)
-      /* The kernel sometimes fails to deliver SIGHUP for ptys.
-         This looks incorrect, but it isn't, because _BSD causes
-         O_NDELAY to be defined in fcntl.h as O_NONBLOCK,
-         and that causes a value other than 0 when there is no input.  */
-      if (nread == 0)
-        return -2;          /* Close this terminal.  */
-#endif
-    }
-  while (
-         /* We used to retry the read if it was interrupted.
-            But this does the wrong thing when O_NONBLOCK causes
-            an EAGAIN error.  Does anybody know of a situation
-            where a retry is actually needed?  */
-#if 0
-         nread < 0 && (errno == EAGAIN || errno == EFAULT
-#ifdef EBADSLT
-                       || errno == EBADSLT
-#endif
-                       )
-#else
-         0
+  nread = emacs_read (fileno (tty->input), (char *) cbuf, n_to_read);
+  /* POSIX infers that processes which are not in the session leader's
+     process group won't get SIGHUPs at logout time.  BSDI adheres to
+     this part standard and returns -1 from read (0) with errno==EIO
+     when the control tty is taken away.
+     Jeffrey Honig <jch@bsdi.com> says this is generally safe.  */
+  if (nread == -1 && errno == EIO)
+    return -2;          /* Close this terminal.  */
+#if defined AIX && defined _BSD
+  /* The kernel sometimes fails to deliver SIGHUP for ptys.
+     This looks incorrect, but it isn't, because _BSD causes
+     O_NDELAY to be defined in fcntl.h as O_NONBLOCK,
+     and that causes a value other than 0 when there is no input.  */
+  if (nread == 0)
+    return -2;          /* Close this terminal.  */
 #endif
-         );
 
 #ifndef USABLE_FIONREAD
 #if defined (USG) || defined (CYGWIN)