Consolidate the function pointer types used by dshash.c.

Commit 8c0d7bafad36434cb08ac2c78e69ae72c194ca20 introduced dshash with hash
and compare functions like DynaHash's, and also variants that take a user
data pointer instead of size.  Simplify the interface by merging them into
a single pair of function pointer types that take both size and a user data
pointer.

Since it is anticipated that memcmp and tag_hash behavior will be a common
requirement, provide wrapper functions dshash_memcmp and dshash_memhash that
conform to the new function types.

Author: Thomas Munro
Reviewed-By: Andres Freund
Discussion: https://postgr.es/m/20170823054644.efuzftxjpfi6wwqs%40alap3.anarazel.de

1 files changed, 10 insertions, 27 deletions

diff --git a/src/include/lib/dshash.h b/src/include/lib/dshash.h
index 187f58b4e49..3fd91f86977 100644
--- a/src/include/lib/dshash.h
+++ b/src/include/lib/dshash.h
@@ -26,32 +26,13 @@ typedef dsa_pointer dshash_table_handle;
 /* The type for hash values. */
 typedef uint32 dshash_hash;
 
-/*
- * A function used for comparing keys.  This version is compatible with
- * HashCompareFunction in hsearch.h and memcmp.
- */
-typedef int (*dshash_compare_function) (const void *a, const void *b, size_t size);
+/* A function type for comparing keys. */
+typedef int (*dshash_compare_function) (const void *a, const void *b,
+										size_t size, void *arg);
 
-/*
- * A function type used for comparing keys.  This version allows compare
- * functions to receive a pointer to arbitrary user data that was given to the
- * create or attach function.  Similar to qsort_arg_comparator.
- */
-typedef int (*dshash_compare_arg_function) (const void *a, const void *b, void *arg);
-
-/*
- * A function type for computing hash values for keys.  This version is
- * compatible with HashValueFunc in hsearch.h and hash functions like
- * tag_hash.
- */
-typedef dshash_hash (*dshash_hash_function) (const void *v, size_t size);
-
-/*
- * A function type for computing hash values for keys.  This version allows
- * hash functions to receive a pointer to arbitrary user data that was given
- * to the create or attach function.
- */
-typedef dshash_hash (*dshash_hash_arg_function) (const void *v, void *arg);
+/* A function type for computing hash values for keys. */
+typedef dshash_hash (*dshash_hash_function) (const void *v, size_t size,
+											 void *arg);
 
 /*
  * The set of parameters needed to create or attach to a hash table.  The
@@ -70,9 +51,7 @@ typedef struct dshash_parameters
 	size_t		key_size;		/* Size of the key (initial bytes of entry) */
 	size_t		entry_size;		/* Total size of entry */
 	dshash_compare_function compare_function;	/* Compare function */
-	dshash_compare_arg_function compare_arg_function;	/* Arg version */
 	dshash_hash_function hash_function; /* Hash function */
-	dshash_hash_arg_function hash_arg_function; /* Arg version */
 	int			tranche_id;		/* The tranche ID to use for locks */
 } dshash_parameters;
 
@@ -101,6 +80,10 @@ extern bool dshash_delete_key(dshash_table *hash_table, const void *key);
 extern void dshash_delete_entry(dshash_table *hash_table, void *entry);
 extern void dshash_release_lock(dshash_table *hash_table, void *entry);
 
+/* Convenience hash and compare functions wrapping memcmp and tag_hash. */
+extern int dshash_memcmp(const void *a, const void *b, size_t size, void *arg);
+extern dshash_hash dshash_memhash(const void *v, size_t size, void *arg);
+
 /* Debugging support. */
 extern void dshash_dump(dshash_table *hash_table);