itree.c: Make the iterator reentrant (bug#59183)

Get rid of the global iterator object and instead allocate
a separate iterator for every loop.  This still uses the "duplicate
iterator" code, including the old iterator which needs a stack,
make ITREE_FOREACH a bit more expensive than we'd like.

* src/itree.h (init_itree, forget_itree, itree_iterator_busy_p):
Delete declarations.
(itree_iterator_start): Add iterator arg and remove `line` and `file` args.
(struct itree_iterator): Move from `itree.c`.  Remove `line` and
`file` fields.
(ITREE_FOREACH): Stack allocate an iterator object and pass it to
`itree_iterator_start`.

* src/itree.c (struct itree_iterator): Move to itree.h.
(iter): Delete global variable.
(itree_iterator_create, init_itree, forget_itree, itree_iterator_busy_p):
Delete functions.
(itree_contains): Adjust assertion.
(itree_iterator_finish): Deallocate the iterator's stack.
(itree_iterator_start): Take the (uninitialized) iterator as argument.
Allocate a fresh new stack.  Remove `file` and `line` arguments.
Don't check `running` any more since the iterator is not expected to be
initialized at all.

* src/eval.c (signal_or_quit):
* src/alloc.c (garbage_collect): Don't check `itree_iterator_busy_p`
any more.

* src/emacs.c (main): No need to `init_itree` any more.
(Fdump_emacs): No need to `forget_itree` any more.

1 files changed, 25 insertions, 21 deletions

diff --git a/src/itree.h b/src/itree.h
index dc448233224..37cd423d34a 100644
--- a/src/itree.h
+++ b/src/itree.h
@@ -107,10 +107,6 @@ enum itree_order
     ITREE_POST_ORDER,
   };
 
-extern void init_itree (void);
-#ifdef HAVE_UNEXEC
-extern void forget_itree (void);
-#endif
 extern void itree_node_init (struct itree_node *, bool, bool, Lisp_Object);
 extern ptrdiff_t itree_node_begin (struct itree_tree *, struct itree_node *);
 extern ptrdiff_t itree_node_end (struct itree_tree *, struct itree_node *);
@@ -129,17 +125,28 @@ extern void itree_delete_gap (struct itree_tree *, ptrdiff_t, ptrdiff_t);
 
 /* Iteration functions.  Almost all code should use ITREE_FOREACH
    instead.  */
-extern bool itree_iterator_busy_p (void);
-extern struct itree_iterator *itree_iterator_start (struct itree_tree *,
+extern struct itree_iterator *itree_iterator_start (struct itree_iterator *,
+                                                    struct itree_tree *,
                                                     ptrdiff_t,
                                                     ptrdiff_t,
-                                                    enum itree_order,
-                                                    const char *, int);
+                                                    enum itree_order);
 extern void itree_iterator_narrow (struct itree_iterator *, ptrdiff_t,
                                    ptrdiff_t);
 extern void itree_iterator_finish (struct itree_iterator *);
 extern struct itree_node *itree_iterator_next (struct itree_iterator *);
 
+/* State used when iterating interval. */
+struct itree_iterator
+  {
+    struct itree_node *node; /* FIXME: It should be either `node` or `stack`. */
+    struct itree_stack *stack;
+    ptrdiff_t begin;
+    ptrdiff_t end;
+    uintmax_t otick;    /* A copy of the tree's `otick`.  */
+    enum itree_order order;
+    bool running;
+  };
+
 /* Iterate over the intervals between BEG and END in the tree T.
    N will hold successive nodes.  ORDER can be one of : `ASCENDING`,
    `DESCENDING`, or `PRE_ORDER`.
@@ -153,29 +160,26 @@ extern struct itree_node *itree_iterator_next (struct itree_iterator *);
    BEWARE:
    - The expression T may be evaluated more than once, so make sure
      it is cheap and pure.
-   - Only a single iteration can happen at a time, so make sure none of the
-     code within the loop can start another tree iteration, i.e. it shouldn't
-     be able to run ELisp code, nor GC since GC can run ELisp by way
-     of `post-gc-hook`.
    - If you need to exit the loop early, you *have* to call `ITREE_ABORT`
      just before exiting (e.g. with `break` or `return`).
    - Non-local exits are not supported within the body of the loop.
    - Don't modify the tree during the iteration.
  */
 #define ITREE_FOREACH(n, t, beg, end, order)                        \
-  /* FIXME: We'd want to declare `x` right here, but I can't figure out
+  /* FIXME: We'd want to declare `n` right here, but I can't figure out
      how to make that work here: the `for` syntax only allows a single
      clause for the var declarations where we need 2 different types.
      We could use the `struct {foo x; bar y; } p;` trick to declare two
      vars `p.x` and `p.y` of unrelated types, but then none of the names
-     of the vars matches the `n` we receive :-(.  */                \
-  if (!t)                                                           \
-    { }                                                             \
-  else                                                              \
-    for (struct itree_iterator *itree_iter_                         \
-            = itree_iterator_start (t, beg, end, ITREE_##order,     \
-                                        __FILE__, __LINE__);        \
-          ((n = itree_iterator_next (itree_iter_))                  \
+     of the vars matches the `n` we receive :-(.  */             \
+  if (!t)                                                        \
+    { }                                                          \
+  else                                                           \
+    for (struct itree_iterator itree_local_iter_,                \
+                               *itree_iter_                      \
+            = itree_iterator_start (&itree_local_iter_,          \
+                                    t, beg, end, ITREE_##order); \
+          ((n = itree_iterator_next (itree_iter_))               \
            || (itree_iterator_finish (itree_iter_), false));)
 
 #define ITREE_FOREACH_ABORT() \