* Resolves: bug #735464 Fix the loop limit used to initialize the table directory, was based on count, now limited to segment_count.

* Do not pre-allocate all buckets based on requested table size. This
  defeats the point of a dynamic hash table which adjusts it's memory
  usage depending upon the number of items it holds. Pre-allocation
  also runs afoul of the table contraction logic, if the table is
  pre-allocated to a large size it will subsequently try to compact it
  negating the pre-allocation. Now the initial allocation is
  restricted to one directory segment (i.e. table->segment_count == 1)

* If the caller did not specify the directory_bits and segment_bits
  then compute them from the requested table size. The directory_size
  and segment_size must be powers of 2 to accmodate fast
  arithmetic. An optimal maximum number of buckets would be equal to
  the anticipated table size. If there were no collisions that would
  mean each item would be located in it's own bucket whose chain
  length is 1, the item would be immediatly found upon indexing into
  the bucket table.

* There is a requirment there be at least one directory
  segment, however contract_table() failed to enforce this
  requirement. Add a check to enforce the requirement.

* If hash_create() or hash_create_ex() failed it left the tbl
  parameter uninitialized but returned an error code. Now upon failure
  tbl is initialized to NULL as well as returning an error code.

* Clean up how the directory and segment sizes were computed. It had
  been using a loop and shifting 1 bit at a time, now it shifts all
  the bits in one operation and assures at least one directory and
  segment are allocated.

* In the event of an early exit from hash_create_ex() due to an error
  make sure all previously allocated resources are cleaned up by
  calling hash_destroy(). There was only one place this was
  missing. hash_destroy() blindly assumed the table had a directory,
  normally it would unless hash_destroy was called due to an early
  exit in hash_create_ex(). Modify hash_destroy() to check for the
  existence of the directory before cleaning up the directory
  contents.

* Update the function documentation in dhash.h to explain each
  parameter of hash_create() and hash_create_ex().

* Enhance dhash_test.c
  - To output the random seed used to intialize the random number
    generator and add command line option to set the random seed. This
    permits recreating a failed test run.
  - Add command line parameter to set the initial table size.
  - Use proper string to long conversion routines when reading command
    line parameters (e.g. strtoul() instead of atoi())
  - Add logic to make sure each test value is unique.

* Add additional information to the debug output to show the computed
  directory_bits, segment_bits, sizes, etc.

* Adjust the debug_level conditionals to be less verbose.

1 files changed, 87 insertions, 46 deletions

diff --git a/dhash/dhash.c b/dhash/dhash.c
index f92e463..79f9c38 100644
--- a/dhash/dhash.c
+++ b/dhash/dhash.c
@@ -53,10 +53,13 @@
 #define PRIME_1                 37
 #define PRIME_2                 1048583
 
- /*
-  * Fast arithmetic, relying on powers of 2, and on pre-processor
-  * concatenation property
-  */
+#ifndef MIN
+    #define MIN(a,b) (((a) < (b)) ? (a) : (b))
+#endif
+
+#ifndef MAX
+    #define MAX(a,b) (((a) > (b)) ? (a) : (b))
+#endif
 
 #define halloc(table, size) table->halloc(size, table->halloc_pvt)
 #define hfree(table, ptr) table->hfree(ptr, table->halloc_pvt)
@@ -247,7 +250,7 @@ static int expand_table(hash_table_t *table)
 
     if (table->bucket_count < (table->directory_size << table->segment_size_shift)) {
 #ifdef DEBUG
-        if (debug_level >= 1)
+        if (debug_level >= 2)
             fprintf(stderr, "expand_table on entry: bucket_count=%lu, segment_count=%lu p=%lu maxp=%lu\n",
                     table->bucket_count, table->segment_count, table->p, table->maxp);
 #endif
@@ -314,7 +317,7 @@ static int expand_table(hash_table_t *table)
             }
         }
 #ifdef DEBUG
-        if (debug_level >= 1)
+        if (debug_level >= 2)
             fprintf(stderr, "expand_table on exit: bucket_count=%lu, segment_count=%lu p=%lu maxp=%lu\n",
                     table->bucket_count, table->segment_count, table->p, table->maxp);
 #endif
@@ -330,9 +333,9 @@ static int contract_table(hash_table_t *table)
     segment_t *old_segment, *new_segment;
     element_t *current;
 
-    if (table->bucket_count > table->segment_size) {
+    if ((table->bucket_count > table->segment_size) && (table->segment_count > 1)) {
 #ifdef DEBUG
-        if (debug_level >= 1)
+        if (debug_level >= 2)
             fprintf(stderr, "contract_table on entry: bucket_count=%lu, segment_count=%lu p=%lu maxp=%lu\n",
                     table->bucket_count, table->segment_count, table->p, table->maxp);
 #endif
@@ -395,7 +398,7 @@ static int contract_table(hash_table_t *table)
         }
 
 #ifdef DEBUG
-        if (debug_level >= 1)
+        if (debug_level >= 2)
             fprintf(stderr, "contract_table on exit: bucket_count=%lu, segment_count=%lu p=%lu maxp=%lu\n",
                     table->bucket_count, table->segment_count, table->p, table->maxp);
 #endif
@@ -428,7 +431,7 @@ static int lookup(hash_table_t *table, hash_key_t *key, element_t **element_arg,
     current_segment = table->directory[segment_dir];
 
 #ifdef DEBUG
-    if (debug_level >= 2)
+    if (debug_level >= 3)
         fprintf(stderr, "lookup: h=%lu, segment_dir=%lu, segment_index=%lu current_segment=%p\n",
                 h, segment_dir, segment_index, current_segment);
 #endif
@@ -505,19 +508,47 @@ int hash_create_ex(unsigned long count, hash_table_t **tbl,
                    hash_free_func *free_func,
                    void *alloc_private_data,
                    hash_delete_callback *delete_callback,
-                   void *delete_private_data)
-{
+                   void *delete_private_data) {
     unsigned long i;
-    unsigned int n_addr_bits;
+    unsigned int n_addr_bits, requested_bits;
+    unsigned int requested_directory_bits;
+    unsigned int requested_segment_bits;
     address_t addr;
     hash_table_t *table = NULL;
 
+    /* Initialize to NULL in case of an early return due to an error */
+    *tbl = NULL;
+
     if (alloc_func == NULL) alloc_func = sys_malloc_wrapper;
     if (free_func == NULL) free_func = sys_free_wrapper;
 
     /* Compute directory and segment parameters */
-    if (directory_bits == 0) directory_bits = HASH_DEFAULT_DIRECTORY_BITS;
-    if (segment_bits == 0) segment_bits = HASH_DEFAULT_SEGMENT_BITS;
+
+    /* compute power of 2 >= count; it's the number of requested buckets */
+    if (count > 1) {
+        for (requested_bits = 0; (1 << requested_bits) < count; requested_bits++);
+    } else {
+        requested_bits = 1;
+    }
+
+    /*
+     * If caller didn't specify directory & segment allocation then
+     * compute it from the requested count.
+     */
+    if (directory_bits == 0 || segment_bits == 0) {
+        /* Equally divide buckets between the directory and segments */
+        requested_directory_bits = MAX(requested_bits >> 1, 1);
+        requested_segment_bits = MAX(requested_bits - requested_directory_bits, 1);
+
+        /* If the requested count wasn't specified pick a default */
+        if (count == 0) {
+            directory_bits = MAX(requested_directory_bits, HASH_DEFAULT_DIRECTORY_BITS);
+            segment_bits = MAX(requested_segment_bits, HASH_DEFAULT_SEGMENT_BITS);
+        } else {
+            directory_bits = requested_directory_bits;
+            segment_bits = requested_segment_bits;
+        }
+    }
 
     for (addr = ~0, n_addr_bits = 0; addr; addr >>= 1, n_addr_bits++);
 
@@ -534,45 +565,46 @@ int hash_create_ex(unsigned long count, hash_table_t **tbl,
     table->halloc_pvt = alloc_private_data;
 
     table->directory_size_shift = directory_bits;
-    for (i = 0, table->directory_size = 1; i < table->directory_size_shift; i++, table->directory_size <<= 1);
+    table->directory_size = directory_bits ? 1 << directory_bits : 0;
 
     table->segment_size_shift = segment_bits;
-    for (i = 0, table->segment_size = 1; i < table->segment_size_shift; i++, table->segment_size <<= 1);
-
+    table->segment_size = segment_bits ? 1 << segment_bits : 0;
 
     /* Allocate directory */
     table->directory = (segment_t **)halloc(table, table->directory_size * sizeof(segment_t *));
     if (table->directory == NULL) {
+        hash_destroy(table);
         return HASH_ERROR_NO_MEMORY;
     }
     memset(table->directory, 0, table->directory_size * sizeof(segment_t *));
 
     /*
-     * Adjust count to be nearest higher power of 2, minimum SEGMENT_SIZE, then
-     * convert into segments.
+     * If one wanted to pre-allocate all the buckets necessary to meet the needs
+     * of the requested count it would be done like this:
+     *
+     * table->segment_count = MIN((count + table->segment_size-1) / table->segment_size,
+     *                            table->directory_size);
+     *
+     * But with dynamic hash tables there is little point to this, the whole idea is to
+     * allow the table to grow/shrink dynamically, therefore we start with just one
+     * segment of buckets, the minimum necessary.
      */
-    i = table->segment_size;
-    while (i < count)
-        i <<= 1;
-    count = i >> table->segment_size_shift;
-
-    table->segment_count = 0;
+    table->segment_count = 1;
     table->p = 0;
     table->entry_count = 0;
     table->delete_callback = delete_callback;
     table->delete_pvt = delete_private_data;
 
     /*
-     * Allocate initial 'i' segments of buckets
+     * Allocate initial segments of buckets
      */
-    for (i = 0; i < count; i++) {
+    for (i = 0; i < table->segment_count; i++) {
         table->directory[i] = (segment_t *)halloc(table, table->segment_size * sizeof(segment_t));
         if (table->directory[i] == NULL) {
             hash_destroy(table);
             return HASH_ERROR_NO_MEMORY;
         }
         memset(table->directory[i], 0, table->segment_size * sizeof(segment_t));
-        table->segment_count++;
     }
     table->bucket_count = table->segment_count << table->segment_size_shift;
     table->maxp = table->bucket_count;
@@ -580,9 +612,16 @@ int hash_create_ex(unsigned long count, hash_table_t **tbl,
     table->max_load_factor = max_load_factor == 0 ? HASH_DEFAULT_MAX_LOAD_FACTOR : max_load_factor;
 
 #if DEBUG
-    if (debug_level >= 1)
-        fprintf(stderr, "hash_create_ex: table=%p count=%lu maxp=%lu segment_count=%lu\n",
-                table, count, table->maxp, table->segment_count);
+    if (debug_level >= 1) {
+        fprintf(stderr, "hash_create_ex: count=%lu available buckets=%lu bucket_count=%lu maxp=%lu\n",
+                count, table->directory_size*table->segment_size, table->bucket_count, table->maxp);
+        fprintf(stderr, "                directory_bits=%u segment_bits=%u requested_bits=%u\n",
+                directory_bits, segment_bits, requested_bits);
+        fprintf(stderr, "                directory_size=%lu segment_size=%lu segment_count=%lu\n",
+                table->directory_size, table->segment_size, table->segment_count);
+        fprintf(stderr, "                min_load_factor=%lu max_load_factor=%lu\n",
+                table->min_load_factor, table->max_load_factor);
+    }
 #endif
 #ifdef HASH_STATISTICS
     memset(&table->statistics, 0, sizeof(table->statistics));
@@ -613,25 +652,27 @@ int hash_destroy(hash_table_t *table)
     if (!table) return HASH_ERROR_BAD_TABLE;
 
     if (table != NULL) {
-        for (i = 0; i < table->segment_count; i++) {
-            /* test probably unnecessary */
-            if ((s = table->directory[i]) != NULL) {
-                for (j = 0; j < table->segment_size; j++) {
-                    p = s[j];
-                    while (p != NULL) {
-                        q = p->next;
-                        hdelete_callback(table, HASH_TABLE_DESTROY, &p->entry);
-                        if (p->entry.key.type == HASH_KEY_STRING) {
-                            hfree(table, (char *)p->entry.key.str);
+        if (table->directory) {
+            for (i = 0; i < table->segment_count; i++) {
+                /* test probably unnecessary */
+                if ((s = table->directory[i]) != NULL) {
+                    for (j = 0; j < table->segment_size; j++) {
+                        p = s[j];
+                        while (p != NULL) {
+                            q = p->next;
+                            hdelete_callback(table, HASH_TABLE_DESTROY, &p->entry);
+                            if (p->entry.key.type == HASH_KEY_STRING) {
+                                hfree(table, (char *)p->entry.key.str);
+                            }
+                            hfree(table, (char *)p);
+                            p = q;
                         }
-                        hfree(table, (char *)p);
-                        p = q;
                     }
+                    hfree(table, s);
                 }
-                hfree(table, s);
             }
+            hfree(table, table->directory);
         }
-        hfree(table, table->directory);
         hfree(table, table);
         table = NULL;
     }