From 2a88ed46e4bf5a240b9fe425598edf6bb158d66b Mon Sep 17 00:00:00 2001
From: Ben Pfaff <blp@cs.stanford.edu>
Date: Sun, 24 Jan 2021 11:35:26 -0800
Subject: [PATCH] llx: Introduce new iteration macros and some users.

---
 src/libpspp/llx.h   | 45 +++++++++++++++++++++++++++++++++++++++++++++
 src/output/driver.c | 21 ++++++++-------------
 2 files changed, 53 insertions(+), 13 deletions(-)

diff --git a/src/libpspp/llx.h b/src/libpspp/llx.h
index 80a8a83806..8f01c70f24 100644
--- a/src/libpspp/llx.h
+++ b/src/libpspp/llx.h
@@ -313,5 +313,50 @@ llx_data (const struct llx *llx)
 {
   return llx->data;
 }
+/* Iteration helper macros. */
+
+/* Sets "struct llx *" NODE to each object in LIST in turn, in forward or
+   reverse order.
+
+   Behavior is undefined if NODE is removed from the list between
+   loop iterations. */
+#define llx_for_each(NODE, LIST)                \
+        for ((NODE) = llx_head (LIST);          \
+             (NODE) != llx_null (LIST);         \
+             (NODE) = llx_next (NODE))
+#define llx_for_each_reverse(NODE, LIST)        \
+        for ((NODE) = llx_tail (LIST);          \
+             (NODE) != llx_null (LIST);         \
+             (NODE) = llx_prev (NODE))
+
+/* Sets "struct llx *" NODE to each object in LIST in turn, in forward or
+   reverse order.  NEXT (or PREV) must be another "struct llx *" variable.
+
+   Behavior is well-defined even if NODE is removed from the list between
+   iterations. */
+#define llx_for_each_safe(NODE, NEXT, LIST)     \
+        for (NODE = llx_head (LIST);            \
+             ((NODE) != llx_null (LIST)         \
+              ? ((NEXT) = llx_next (NODE), 1)   \
+              : 0);                             \
+             (NODE) = (NEXT))
+#define llx_for_each_reverse_safe(NODE, PREV, LIST)     \
+        for (NODE = llx_tail (LIST);                    \
+             ((NODE) != llx_null (LIST)                 \
+              ? ((PREV) = llx_prev (NODE), 1)           \
+              : 0);                                     \
+             (NODE) = (PREV))
+
+/* Sets DATA to the data from each object in LIST in turn, in forward or
+   reverse order.  Each object is removed from LIST before its loop
+   iteration. */
+#define llx_for_each_preremove(DATA, LIST, MANAGER)             \
+        while (!llx_is_empty (LIST)                             \
+               ? ((DATA) = llx_pop_head (LIST, MANAGER), 1)     \
+               : 0)
+#define llx_for_each_reverse_preremove(DATA, LIST, MANAGER)     \
+        while (!llx_is_empty (LIST)                             \
+               ? ((DATA) = llx_pop_tail (LIST, MANAGER), 1)     \
+               : 0)
 
 #endif /* llx.h */
diff --git a/src/output/driver.c b/src/output/driver.c
index 6f5d4633ce..7c0bff8bf5 100644
--- a/src/output/driver.c
+++ b/src/output/driver.c
@@ -110,13 +110,11 @@ void
 output_engine_pop (void)
 {
   struct ll *head = ll_pop_head (&engine_stack);
-  struct output_engine *e =ll_data (head, struct output_engine, ll);
+  struct output_engine *e = ll_data (head, struct output_engine, ll);
 
-  while (!llx_is_empty (&e->drivers))
-    {
-      struct output_driver *d = llx_pop_head (&e->drivers, &llx_malloc_mgr);
-      output_driver_destroy (d);
-    }
+  struct output_driver *d;
+  llx_for_each_preremove (d, &e->drivers, &llx_malloc_mgr)
+    output_driver_destroy (d);
   output_item_unref (e->deferred_text);
   free (e->command_name);
   free (e->title);
@@ -141,13 +139,10 @@ static void
 output_submit__ (struct output_engine *e, struct output_item *item)
 {
   struct llx *llx, *next;
-
-  for (llx = llx_head (&e->drivers); llx != llx_null (&e->drivers); llx = next)
+  llx_for_each_safe (llx, next, &e->drivers)
     {
       struct output_driver *d = llx_data (llx);
 
-      next = llx_next (llx);
-
       enum settings_output_type type = SETTINGS_OUTPUT_RESULT;
       switch (item->type)
         {
@@ -299,11 +294,11 @@ void
 output_flush (void)
 {
   struct output_engine *e = engine_stack_top ();
-  struct llx *llx;
 
   flush_deferred_text (e);
-  for (llx = llx_head (&e->drivers); llx != llx_null (&e->drivers);
-       llx = llx_next (llx))
+
+  struct llx *llx;
+  llx_for_each (llx, &e->drivers)
     {
       struct output_driver *d = llx_data (llx);
       if (d->device_type & SETTINGS_DEVICE_TERMINAL && d->class->flush != NULL)
-- 
2.30.2