itable behave like hash_table for double/reduce/cant_iterate

Author: btovar

dttools/src/itable.c

@@ -6,12 +6,14 @@ See the file COPYING for details.
 */
 
 #include "itable.h"
+#include "debug.h"
 
 #include <stdlib.h>
 #include <string.h>
 
 #define DEFAULT_SIZE 127
-#define DEFAULT_LOAD 0.75
+#define DEFAULT_MAX_LOAD 0.75
+#define DEFAULT_MIN_LOAD 0.125
 
 struct entry {
 	UINT64_T key;
@@ -25,6 +27,14 @@ struct itable {
 	struct entry **buckets;
 	int ibucket;
 	struct entry *ientry;
+
+	/* for memory safety, itable_nextkey cannot be called in the same
+	 * iteration if itable_insert or itable_remove has been called.
+	 * In such case, the executable will be terminated with a fatal message.
+	 * If the table should be modified during iterations, consider
+	 * using the array keys from itable_keys_array. (If so, remember
+	 * to free it afterwards with itable_free_keys_array.) */
+	int cant_iterate_yet;
 };
 
 struct itable *itable_create(int bucket_count)
@@ -46,6 +56,7 @@ struct itable *itable_create(int bucket_count)
 	}
 
 	h->size = 0;
+	h->cant_iterate_yet = 0;
 
 	return h;
 }
@@ -69,6 +80,9 @@ void itable_clear(struct itable *h, void (*delete_func)(void *))
 	for (i = 0; i < h->bucket_count; i++) {
 		h->buckets[i] = 0;
 	}
+
+	/* buckets went away, thus a nextkey would be invalid */
+	h->cant_iterate_yet = 1;
 }
 
 void itable_delete(struct itable *h)
@@ -78,11 +92,63 @@ void itable_delete(struct itable *h)
 	free(h);
 }
 
+UINT64_T *itable_keys_array(struct itable *h)
+{
+	UINT64_T *keys = (UINT64_T *)malloc(sizeof(int) * h->size);
+	int ikey = 0;
+
+	struct entry *e, *f;
+	int i;
+
+	for (i = 0; i < h->bucket_count; i++) {
+		e = h->buckets[i];
+		while (e) {
+			keys[ikey] = e->key;
+			ikey++;
+			f = e->next;
+			e = f;
+		}
+	}
+
+	return keys;
+}
+
+void itable_free_keys_array(UINT64_T *keys)
+{
+	free(keys);
+}
+
 int itable_size(struct itable *h)
 {
 	return h->size;
 }
 
+double itable_load(struct itable *h)
+{
+	return (double)h->size / h->bucket_count;
+}
+
+static int insert_to_buckets_aux(struct entry **buckets, int bucket_count, struct entry *new_entry)
+{
+	unsigned index;
+	struct entry *e;
+
+	index = new_entry->key % bucket_count;
+	e = buckets[index];
+
+	while (e) {
+		/* check that this key does not already exist in the table */
+		if (new_entry->key == e->key) {
+			return 0;
+		}
+		e = e->next;
+	}
+
+	new_entry->next = buckets[index];
+	buckets[index] = new_entry;
+	return 1;
+}
+
 void *itable_lookup(struct itable *h, UINT64_T key)
 {
 	struct entry *e;
@@ -103,73 +169,96 @@ void *itable_lookup(struct itable *h, UINT64_T key)
 
 static int itable_double_buckets(struct itable *h)
 {
-	struct itable *hn = itable_create(2 * h->bucket_count);
-
-	if (!hn)
+	int new_count = (2 * (h->bucket_count + 1)) - 1;
+	struct entry **new_buckets = (struct entry **)calloc(new_count, sizeof(struct entry *));
+	if (!new_buckets) {
 		return 0;
+	}
 
-	/* Move pairs to new hash */
-	uint64_t key;
-	void *value;
-	itable_firstkey(h);
-	while (itable_nextkey(h, &key, &value))
-		if (!itable_insert(hn, key, value)) {
-			itable_delete(hn);
-			return 0;
-		}
-
-	/* Delete all old pairs */
 	struct entry *e, *f;
-	int i;
-	for (i = 0; i < h->bucket_count; i++) {
+	for (int i = 0; i < h->bucket_count; i++) {
 		e = h->buckets[i];
 		while (e) {
 			f = e->next;
-			free(e);
+			e->next = NULL;
+			insert_to_buckets_aux(new_buckets, new_count, e);
 			e = f;
 		}
 	}
 
 	/* Make the old point to the new */
 	free(h->buckets);
-	h->buckets = hn->buckets;
-	h->bucket_count = hn->bucket_count;
-	h->size = hn->size;
+	h->buckets = new_buckets;
+	h->bucket_count = new_count;
 
-	/* Delete reference to new, so old is safe */
-	free(hn);
+	/* structure of itable changed completely, thus a nextkey would be incorrect. */
+	h->cant_iterate_yet = 1;
 
 	return 1;
 }
 
 int itable_insert(struct itable *h, UINT64_T key, const void *value)
 {
-	struct entry *e;
-	UINT64_T index;
-
-	if (((float)h->size / h->bucket_count) > DEFAULT_LOAD)
+	if (((float)h->size / h->bucket_count) > DEFAULT_MAX_LOAD)
 		itable_double_buckets(h);
 
-	index = key % h->bucket_count;
-	e = h->buckets[index];
+	struct entry *new_entry = (struct entry *)malloc(sizeof(struct entry));
+	if (!new_entry)
+		return 0;
 
-	while (e) {
-		if (key == e->key) {
-			e->value = (void *)value;
-			return 1;
-		}
-		e = e->next;
+	new_entry->key = key;
+	new_entry->value = (void *)value;
+
+	int inserted = insert_to_buckets_aux(h->buckets, h->bucket_count, new_entry);
+	if (inserted) {
+		h->size++;
+		/* inserting cause different behaviours with nextkey (e.g., sometimes the new
+		 * key would be included or skipped in the iteration */
+		h->cant_iterate_yet = 1;
+
+		return 1;
+	}
+
+	return 0;
+}
+
+static int itable_reduce_buckets(struct itable *h)
+{
+	int new_count = ((h->bucket_count + 1) / 2) - 1;
+
+	/* DEFAULT_SIZE is the minimum size */
+	if (new_count < DEFAULT_SIZE) {
+		return 1;
 	}
 
-	e = (struct entry *)malloc(sizeof(struct entry));
-	if (!e)
+	/* Table cannot be reduced above DEFAULT_MAX_LOAD */
+	if (((float)h->size / new_count) > DEFAULT_MAX_LOAD) {
+		return 1;
+	}
+
+	struct entry **new_buckets = (struct entry **)calloc(new_count, sizeof(struct entry *));
+	if (!new_buckets) {
 		return 0;
+	}
 
-	e->key = key;
-	e->value = (void *)value;
-	e->next = h->buckets[index];
-	h->buckets[index] = e;
-	h->size++;
+	struct entry *e, *f;
+	for (int i = 0; i < h->bucket_count; i++) {
+		e = h->buckets[i];
+		while (e) {
+			f = e->next;
+			e->next = NULL;
+			insert_to_buckets_aux(new_buckets, new_count, e);
+			e = f;
+		}
+	}
+
+	/* Make the old point to the new */
+	free(h->buckets);
+	h->buckets = new_buckets;
+	h->bucket_count = new_count;
+
+	/* structure of itable changed completely, thus a nextkey would be incorrect. */
+	h->cant_iterate_yet = 1;
 
 	return 1;
 }
@@ -194,6 +283,12 @@ void *itable_remove(struct itable *h, UINT64_T key)
 			value = e->value;
 			free(e);
 			h->size--;
+			h->cant_iterate_yet = 1;
+
+			if (((float)h->size / h->bucket_count) < DEFAULT_MIN_LOAD) {
+				itable_reduce_buckets(h);
+			}
+
 			return value;
 		}
 		f = e;
@@ -218,6 +313,8 @@ void *itable_pop(struct itable *t)
 
 void itable_firstkey(struct itable *h)
 {
+	h->cant_iterate_yet = 0;
+
 	h->ientry = 0;
 	for (h->ibucket = 0; h->ibucket < h->bucket_count; h->ibucket++) {
 		h->ientry = h->buckets[h->ibucket];
@@ -228,6 +325,10 @@ void itable_firstkey(struct itable *h)
 
 int itable_nextkey(struct itable *h, UINT64_T *key, void **value)
 {
+	if (h->cant_iterate_yet) {
+		fatal("cctools bug: the itable iteration has not been reset since last modification");
+	}
+
 	if (h->ientry) {
 		*key = h->ientry->key;
 		if (value)

dttools/src/itable.h

@@ -69,13 +69,39 @@ Note that this function will not delete all of the objects contained within the
 
 void itable_delete(struct itable *h);
 
+
+/** Return an array with all the current keys.
+It is the responsibility of the caller to free this array with
+itable_free_keys_array.
+@param h A pointer to a hash table.
+@return An array of all the current keys.
+*/
+
+UINT64_T *itable_keys_array(struct itable *h);
+
+
+/** Free an array generated from itable_free_keys_array.
+@param keys An array of all the keys.
+*/
+
+void itable_free_keys_array(UINT64_T *keys);
+
+
 /** Count the entries in an integer table.
 @return The number of entries in the table.
 @param h A pointer to an integer table.
 */
 
 int itable_size(struct itable *h);
 
+/** Get the proportion of elements vs buckets in the table.
+@return The load of the table.
+@param h A pointer to an integer table.
+*/
+
+double itable_load(struct itable *h);
+
+
 /** Insert a key and value.
 This call will fail if the table already contains the same key.
 You must call @ref itable_remove to remove it.