Expand palloc/pg_malloc API for more type safety

petere · petere · commit 2016055a92f2 · 2022-09-12T08:45:03.000+02:00
This adds additional variants of palloc, pg_malloc, etc. that encapsulate common usage patterns and provide more type safety. Specifically, this adds palloc_object(), palloc_array(), and repalloc_array(), which take the type name of the object to be allocated as its first argument and cast the return as a pointer to that type. There are also palloc0_object() and palloc0_array() variants for initializing with zero, and pg_malloc_*() variants of all of the above. Inspired by the talloc library. Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us> Discussion: https://www.postgresql.org/message-id/flat/bb755632-2a43-d523-36f8-a1e7a389a907@enterprisedb.com
diff --git a/src/include/common/fe_memutils.h b/src/include/common/fe_memutils.h
@@ -29,6 +29,28 @@ extern void *pg_malloc_extended(size_t size, int flags);
 extern void *pg_realloc(void *pointer, size_t size);
 extern void pg_free(void *pointer);
 
+/*
+ * Variants with easier notation and more type safety
+ */
+
+/*
+ * Allocate space for one object of type "type"
+ */
+#define pg_malloc_object(type) ((type *) pg_malloc(sizeof(type)))
+#define pg_malloc0_object(type) ((type *) pg_malloc0(sizeof(type)))
+
+/*
+ * Allocate space for "count" objects of type "type"
+ */
+#define pg_malloc_array(type, count) ((type *) pg_malloc(sizeof(type) * (count)))
+#define pg_malloc0_array(type, count) ((type *) pg_malloc0(sizeof(type) * (count)))
+
+/*
+ * Change size of allocation pointed to by "pointer" to have space for "count"
+ * objects of type "type"
+ */
+#define pg_realloc_array(pointer, type, count) ((type *) pg_realloc(pointer, sizeof(type) * (count)))
+
 /* Equivalent functions, deliberately named the same as backend functions */
 extern char *pstrdup(const char *in);
 extern char *pnstrdup(const char *in, Size size);
@@ -38,6 +60,12 @@ extern void *palloc_extended(Size size, int flags);
 extern void *repalloc(void *pointer, Size size);
 extern void pfree(void *pointer);
 
+#define palloc_object(type) ((type *) palloc(sizeof(type)))
+#define palloc0_object(type) ((type *) palloc0(sizeof(type)))
+#define palloc_array(type, count) ((type *) palloc(sizeof(type) * (count)))
+#define palloc0_array(type, count) ((type *) palloc0(sizeof(type) * (count)))
+#define repalloc_array(pointer, type, count) ((type *) repalloc(pointer, sizeof(type) * (count)))
+
 /* sprintf into a palloc'd buffer --- these are in psprintf.c */
 extern char *psprintf(const char *fmt,...) pg_attribute_printf(1, 2);
 extern size_t pvsnprintf(char *buf, size_t len, const char *fmt, va_list args) pg_attribute_printf(3, 0);
diff --git a/src/include/utils/palloc.h b/src/include/utils/palloc.h
@@ -80,6 +80,28 @@ extern void *palloc_extended(Size size, int flags);
 extern pg_nodiscard void *repalloc(void *pointer, Size size);
 extern void pfree(void *pointer);
 
+/*
+ * Variants with easier notation and more type safety
+ */
+
+/*
+ * Allocate space for one object of type "type"
+ */
+#define palloc_object(type) ((type *) palloc(sizeof(type)))
+#define palloc0_object(type) ((type *) palloc0(sizeof(type)))
+
+/*
+ * Allocate space for "count" objects of type "type"
+ */
+#define palloc_array(type, count) ((type *) palloc(sizeof(type) * (count)))
+#define palloc0_array(type, count) ((type *) palloc0(sizeof(type) * (count)))
+
+/*
+ * Change size of allocation pointed to by "pointer" to have space for "count"
+ * objects of type "type"
+ */
+#define repalloc_array(pointer, type, count) ((type *) repalloc(pointer, sizeof(type) * (count)))
+
 /*
  * The result of palloc() is always word-aligned, so we can skip testing
  * alignment of the pointer when deciding which MemSet variant to use.
