From 2733e649b31b5491fb252970a06dc9abb3838e4c Mon Sep 17 00:00:00 2001
From: Ben Pfaff <blp@cs.stanford.edu>
Date: Fri, 11 Oct 2019 04:15:45 +0000
Subject: [PATCH] pivot-table: Add reference counts.

This will be more useful in an upcoming commit.
---
 src/language/dictionary/sys-file-info.c |  2 +-
 src/language/stats/crosstabs.q          |  2 +-
 src/output/pivot-output.c               |  2 +-
 src/output/pivot-table.c                | 28 +++++++++++++++++++++++--
 src/output/pivot-table.h                | 10 ++++++++-
 5 files changed, 38 insertions(+), 6 deletions(-)

diff --git a/src/language/dictionary/sys-file-info.c b/src/language/dictionary/sys-file-info.c
index d8a37cdd65..5d47725b57 100644
--- a/src/language/dictionary/sys-file-info.c
+++ b/src/language/dictionary/sys-file-info.c
@@ -706,7 +706,7 @@ display_attributes (const struct attrset *dict_attrset,
                      var_get_attributes (vars[i]), flags);
 
   if (pivot_table_is_empty (table))
-    pivot_table_destroy (table);
+    pivot_table_unref (table);
   else
     pivot_table_submit (table);
 }
diff --git a/src/language/stats/crosstabs.q b/src/language/stats/crosstabs.q
index b87acf4c72..6defd2447a 100644
--- a/src/language/stats/crosstabs.q
+++ b/src/language/stats/crosstabs.q
@@ -1097,7 +1097,7 @@ output_crosstabulation (struct crosstabs_proc *proc, struct crosstabulation *xt)
       if (!pivot_table_is_empty (risk))
         pivot_table_submit (risk);
       else
-        pivot_table_destroy (risk);
+        pivot_table_unref (risk);
     }
 
   if (direct)
diff --git a/src/output/pivot-output.c b/src/output/pivot-output.c
index 69a6f7fec6..f9c22b7785 100644
--- a/src/output/pivot-output.c
+++ b/src/output/pivot-output.c
@@ -512,5 +512,5 @@ pivot_table_submit (struct pivot_table *pt)
 
   settings_set_decimal_char (old_decimal);
 
-  pivot_table_destroy (pt);
+  pivot_table_unref (pt);
 }
diff --git a/src/output/pivot-table.c b/src/output/pivot-table.c
index 72a158baaa..eaad89737b 100644
--- a/src/output/pivot-table.c
+++ b/src/output/pivot-table.c
@@ -638,6 +638,7 @@ struct pivot_table *
 pivot_table_create__ (struct pivot_value *title)
 {
   struct pivot_table *table = xzalloc (sizeof *table);
+  table->ref_cnt = 1;
   table->weight_format = (struct fmt_spec) { FMT_F, 40, 0 };
   table->title = title;
 
@@ -723,12 +724,27 @@ pivot_table_create_for_text (struct pivot_value *title,
   return table;
 }
 
-/* Destroys TABLE and frees everything it points to. */
+/* Increases TABLE's reference count, indicating that it has an additional
+   owner.  A pivot table that is shared among multiple owners must not be
+   modified. */
+struct pivot_table *
+pivot_table_ref (const struct pivot_table *table_)
+{
+  struct pivot_table *table = CONST_CAST (struct pivot_table *, table_);
+  table->ref_cnt++;
+  return table;
+}
+
+/* Decreases TABLE's reference count, indicating that it has one fewer owner.
+   If TABLE no longer has any owners, it is freed. */
 void
-pivot_table_destroy (struct pivot_table *table)
+pivot_table_unref (struct pivot_table *table)
 {
   if (!table)
     return;
+  assert (table->ref_cnt > 0);
+  if (--table->ref_cnt)
+    return;
 
   free (table->current_layer);
   free (table->table_look);
@@ -781,6 +797,14 @@ pivot_table_destroy (struct pivot_table *table)
   free (table);
 }
 
+/* Returns true if TABLE has more than one owner.  A pivot table that is shared
+   among multiple owners must not be modified. */
+bool
+pivot_table_is_shared (const struct pivot_table *table)
+{
+  return table->ref_cnt > 1;
+}
+
 /* Sets the format used for PIVOT_RC_COUNT cells to the one used for variable
    WV, which should be the weight variable for the dictionary whose data or
    statistics are being put into TABLE.
diff --git a/src/output/pivot-table.h b/src/output/pivot-table.h
index aa064953fe..657ec75ede 100644
--- a/src/output/pivot-table.h
+++ b/src/output/pivot-table.h
@@ -372,6 +372,11 @@ bool pivot_result_class_change (const char *, const struct fmt_spec *);
 /* A pivot table.  See the top of this file for more information. */
 struct pivot_table
   {
+    /* Reference count.  A pivot_table may be shared between multiple owners,
+       indicated by a reference count greater than 1.  When this is the case,
+       the pivot_table must not be modified. */
+    int ref_cnt;
+
     /* Display settings. */
     bool rotate_inner_column_labels;
     bool rotate_outer_row_labels;
@@ -448,7 +453,10 @@ struct pivot_table *pivot_table_create (const char *title);
 struct pivot_table *pivot_table_create__ (struct pivot_value *title);
 struct pivot_table *pivot_table_create_for_text (struct pivot_value *title,
                                                  struct pivot_value *content);
-void pivot_table_destroy (struct pivot_table *);
+
+struct pivot_table *pivot_table_ref (const struct pivot_table *);
+void pivot_table_unref (struct pivot_table *);
+bool pivot_table_is_shared (const struct pivot_table *);
 
 /* Format of PIVOT_RC_COUNT cells. */
 void pivot_table_set_weight_var (struct pivot_table *,
-- 
2.30.2