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db_include/storage/shm_toc.h

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+/*-------------------------------------------------------------------------
+ *
+ * shm_toc.h
+ *	  shared memory segment table of contents
+ *
+ * This is intended to provide a simple way to divide a chunk of shared
+ * memory (probably dynamic shared memory allocated via dsm_create) into
+ * a number of regions and keep track of the addresses of those regions or
+ * key data structures within those regions.  This is not intended to
+ * scale to a large number of keys and will perform poorly if used that
+ * way; if you need a large number of pointers, store them within some
+ * other data structure within the segment and only put the pointer to
+ * the data structure itself in the table of contents.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/include/storage/shm_toc.h
+ *
+ *-------------------------------------------------------------------------
+ */
+#ifndef SHM_TOC_H
+#define SHM_TOC_H
+
+#include "storage/shmem.h"		/* for add_size() */
+
+/* shm_toc is an opaque type known only within shm_toc.c */
+typedef struct shm_toc shm_toc;
+
+extern shm_toc *shm_toc_create(uint64 magic, void *address, Size nbytes);
+extern shm_toc *shm_toc_attach(uint64 magic, void *address);
+extern void *shm_toc_allocate(shm_toc *toc, Size nbytes);
+extern Size shm_toc_freespace(shm_toc *toc);
+extern void shm_toc_insert(shm_toc *toc, uint64 key, void *address);
+extern void *shm_toc_lookup(shm_toc *toc, uint64 key, bool noError);
+
+/*
+ * Tools for estimating how large a chunk of shared memory will be needed
+ * to store a TOC and its dependent objects.  Note: we don't really support
+ * large numbers of keys, but it's convenient to declare number_of_keys
+ * as a Size anyway.
+ */
+typedef struct
+{
+	Size		space_for_chunks;
+	Size		number_of_keys;
+} shm_toc_estimator;
+
+#define shm_toc_initialize_estimator(e) \
+	((e)->space_for_chunks = 0, (e)->number_of_keys = 0)
+#define shm_toc_estimate_chunk(e, sz) \
+	((e)->space_for_chunks = add_size((e)->space_for_chunks, BUFFERALIGN(sz)))
+#define shm_toc_estimate_keys(e, cnt) \
+	((e)->number_of_keys = add_size((e)->number_of_keys, cnt))
+
+extern Size shm_toc_estimate(shm_toc_estimator *e);
+
+#endif							/* SHM_TOC_H */