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[libvirt] [PATCH] util: Simplify hash implementation



So far first entries for each hash key are stored directly in the hash
table while other entries mapped to the same key are linked through
pointers. As a result of that, the code is cluttered with special
handling for the first items.

Commit 9677cd33eea4c65d78ba463b46b8b45ed2da1709 made it possible to
remove current entry when iterating through all hash entries. However,
it didn't add the special first item handling which could cause libvirtd
crash or hang.

Instead of adding more clutter, this patch fixes the crash by linking
all entries (even the first ones) through pointers which significantly
simplifies the code and makes it more maintainable.
---
 src/util/hash.c |  290 ++++++++++++++++++-------------------------------------
 1 files changed, 94 insertions(+), 196 deletions(-)

diff --git a/src/util/hash.c b/src/util/hash.c
index 48a94ad..dbb34ec 100644
--- a/src/util/hash.c
+++ b/src/util/hash.c
@@ -50,14 +50,13 @@ struct _virHashEntry {
     struct _virHashEntry *next;
     void *name;
     void *payload;
-    int valid;
 };
 
 /*
  * The entire hash table
  */
 struct _virHashTable {
-    struct _virHashEntry *table;
+    virHashEntryPtr *table;
     int size;
     int nbElems;
     /* True iff we are iterating over hash entries. */
@@ -165,7 +164,7 @@ virHashTablePtr virHashCreateFull(int size,
  *
  * Create a new virHashTablePtr.
  *
- * Returns the newly created object, or NULL if an error occured.
+ * Returns the newly created object, or NULL if an error occurred.
  */
 virHashTablePtr virHashCreate(int size, virHashDataFree dataFree)
 {
@@ -189,10 +188,8 @@ virHashTablePtr virHashCreate(int size, virHashDataFree dataFree)
 static int
 virHashGrow(virHashTablePtr table, int size)
 {
-    unsigned long key;
     int oldsize, i;
-    virHashEntryPtr iter, next;
-    struct _virHashEntry *oldtable;
+    virHashEntryPtr *oldtable;
 
 #ifdef DEBUG_GROW
     unsigned long nbElem = 0;
@@ -217,43 +214,18 @@ virHashGrow(virHashTablePtr table, int size)
     }
     table->size = size;
 
-    /* If the two loops are merged, there would be situations where
-     * a new entry needs to allocated and data copied into it from
-     * the main table. So instead, we run through the array twice, first
-     * copying all the elements in the main array (where we can't get
-     * conflicts) and then the rest, so we only free (and don't allocate)
-     */
-    for (i = 0; i < oldsize; i++) {
-        if (oldtable[i].valid == 0)
-            continue;
-        key = virHashComputeKey(table, oldtable[i].name);
-        memcpy(&(table->table[key]), &(oldtable[i]), sizeof(virHashEntry));
-        table->table[key].next = NULL;
-    }
-
     for (i = 0; i < oldsize; i++) {
-        iter = oldtable[i].next;
+        virHashEntryPtr iter = oldtable[i];
         while (iter) {
-            next = iter->next;
+            virHashEntryPtr next = iter->next;
+            unsigned long key = virHashComputeKey(table, iter->name);
 
-            /*
-             * put back the entry in the new table
-             */
-
-            key = virHashComputeKey(table, iter->name);
-            if (table->table[key].valid == 0) {
-                memcpy(&(table->table[key]), iter, sizeof(virHashEntry));
-                table->table[key].next = NULL;
-                VIR_FREE(iter);
-            } else {
-                iter->next = table->table[key].next;
-                table->table[key].next = iter;
-            }
+            iter->next = table->table[key];
+            table->table[key] = iter;
 
 #ifdef DEBUG_GROW
             nbElem++;
 #endif
-
             iter = next;
         }
     }
@@ -279,36 +251,24 @@ void
 virHashFree(virHashTablePtr table)
 {
     int i;
-    virHashEntryPtr iter;
-    virHashEntryPtr next;
-    int inside_table = 0;
-    int nbElems;
 
     if (table == NULL)
         return;
-    if (table->table) {
-        nbElems = table->nbElems;
-        for (i = 0; (i < table->size) && (nbElems > 0); i++) {
-            iter = &(table->table[i]);
-            if (iter->valid == 0)
-                continue;
-            inside_table = 1;
-            while (iter) {
-                next = iter->next;
-                if ((table->dataFree != NULL) && (iter->payload != NULL))
-                    table->dataFree(iter->payload, iter->name);
-                if (table->keyFree)
-                    table->keyFree(iter->name);
-                iter->payload = NULL;
-                if (!inside_table)
-                    VIR_FREE(iter);
-                nbElems--;
-                inside_table = 0;
-                iter = next;
-            }
+
+    for (i = 0; i < table->size; i++) {
+        virHashEntryPtr iter = table->table[i];
+        while (iter) {
+            virHashEntryPtr next = iter->next;
+
+            if (table->dataFree)
+                table->dataFree(iter->payload, iter->name);
+            if (table->keyFree)
+                table->keyFree(iter->name);
+            VIR_FREE(iter);
+            iter = next;
         }
-        VIR_FREE(table->table);
     }
+
     VIR_FREE(table);
 }
 
@@ -319,9 +279,7 @@ virHashAddOrUpdateEntry(virHashTablePtr table, const void *name,
 {
     unsigned long key, len = 0;
     virHashEntryPtr entry;
-    virHashEntryPtr insert;
     char *new_name;
-    bool found;
 
     if ((table == NULL) || (name == NULL))
         return (-1);
@@ -329,67 +287,40 @@ virHashAddOrUpdateEntry(virHashTablePtr table, const void *name,
     if (table->iterating)
         virHashIterationError(-1);
 
-    /*
-     * Check for duplicate and insertion location.
-     */
-    found = false;
     key = virHashComputeKey(table, name);
-    if (table->table[key].valid == 0) {
-        insert = NULL;
-    } else {
-        for (insert = &(table->table[key]); insert->next != NULL;
-             insert = insert->next) {
-            if (table->keyEqual(insert->name, name)) {
-                found = true;
-                break;
-            }
-            len++;
-        }
-        if (table->keyEqual(insert->name, name))
-            found = true;
-    }
-
-    if (found) {
-        if (is_update) {
-            if (table->dataFree)
-                table->dataFree(insert->payload, insert->name);
-            insert->payload = userdata;
-            return (0);
-        } else {
-            return (-1);
-        }
-    }
 
-    if (insert == NULL) {
-        entry = &(table->table[key]);
-    } else {
-        if (VIR_ALLOC(entry) < 0) {
-            virReportOOMError();
-            return (-1);
+    /* Check for duplicate entry */
+    for (entry = table->table[key]; entry; entry = entry->next) {
+        if (table->keyEqual(entry->name, name)) {
+            if (is_update) {
+                if (table->dataFree)
+                    table->dataFree(entry->payload, entry->name);
+                entry->payload = userdata;
+                return 0;
+            } else {
+                return -1;
+            }
         }
+        len++;
     }
 
-    new_name = table->keyCopy(name);
-    if (new_name == NULL) {
+    if (VIR_ALLOC(entry) < 0 || !(new_name = table->keyCopy(name))) {
         virReportOOMError();
-        if (insert != NULL)
-            VIR_FREE(entry);
-        return (-1);
+        VIR_FREE(entry);
+        return -1;
     }
+
     entry->name = new_name;
     entry->payload = userdata;
-    entry->next = NULL;
-    entry->valid = 1;
-
-    if (insert != NULL)
-        insert->next = entry;
+    entry->next = table->table[key];
+    table->table[key] = entry;
 
     table->nbElems++;
 
     if (len > MAX_HASH_LEN)
         virHashGrow(table, MAX_HASH_LEN * table->size);
 
-    return (0);
+    return 0;
 }
 
 /**
@@ -443,18 +374,15 @@ virHashLookup(virHashTablePtr table, const void *name)
     unsigned long key;
     virHashEntryPtr entry;
 
-    if (table == NULL)
-        return (NULL);
-    if (name == NULL)
-        return (NULL);
+    if (!table || !name)
+        return NULL;
+
     key = virHashComputeKey(table, name);
-    if (table->table[key].valid == 0)
-        return (NULL);
-    for (entry = &(table->table[key]); entry != NULL; entry = entry->next) {
+    for (entry = table->table[key]; entry; entry = entry->next) {
         if (table->keyEqual(entry->name, name))
-            return (entry->payload);
+            return entry->payload;
     }
-    return (NULL);
+    return NULL;
 }
 
 
@@ -512,47 +440,31 @@ virHashSize(virHashTablePtr table)
 int
 virHashRemoveEntry(virHashTablePtr table, const void *name)
 {
-    unsigned long key;
     virHashEntryPtr entry;
-    virHashEntryPtr prev = NULL;
+    virHashEntryPtr *nextptr;
 
     if (table == NULL || name == NULL)
         return (-1);
 
-    key = virHashComputeKey(table, name);
-    if (table->table[key].valid == 0) {
-        return (-1);
-    } else {
-        for (entry = &(table->table[key]); entry != NULL;
-             entry = entry->next) {
-            if (table->keyEqual(entry->name, name)) {
-                if (table->iterating && table->current != entry)
-                    virHashIterationError(-1);
-                if (table->dataFree && (entry->payload != NULL))
-                    table->dataFree(entry->payload, entry->name);
-                entry->payload = NULL;
-                if (table->keyFree)
-                    table->keyFree(entry->name);
-                if (prev) {
-                    prev->next = entry->next;
-                    VIR_FREE(entry);
-                } else {
-                    if (entry->next == NULL) {
-                        entry->valid = 0;
-                    } else {
-                        entry = entry->next;
-                        memcpy(&(table->table[key]), entry,
-                               sizeof(virHashEntry));
-                        VIR_FREE(entry);
-                    }
-                }
-                table->nbElems--;
-                return (0);
-            }
-            prev = entry;
+    nextptr = table->table + virHashComputeKey(table, name);
+    for (entry = *nextptr; entry; entry = entry->next) {
+        if (table->keyEqual(entry->name, name)) {
+            if (table->iterating && table->current != entry)
+                virHashIterationError(-1);
+
+            if (table->dataFree)
+                table->dataFree(entry->payload, entry->name);
+            if (table->keyFree)
+                table->keyFree(entry->name);
+            *nextptr = entry->next;
+            VIR_FREE(entry);
+            table->nbElems--;
+            return 0;
         }
-        return (-1);
+        nextptr = &entry->next;
     }
+
+    return -1;
 }
 
 
@@ -581,15 +493,15 @@ int virHashForEach(virHashTablePtr table, virHashIterator iter, void *data)
     table->iterating = true;
     table->current = NULL;
     for (i = 0 ; i < table->size ; i++) {
-        virHashEntryPtr entry = table->table + i;
+        virHashEntryPtr entry = table->table[i];
         while (entry) {
             virHashEntryPtr next = entry->next;
-            if (entry->valid) {
-                table->current = entry;
-                iter(entry->payload, entry->name, data);
-                table->current = NULL;
-                count++;
-            }
+
+            table->current = entry;
+            iter(entry->payload, entry->name, data);
+            table->current = NULL;
+
+            count++;
             entry = next;
         }
     }
@@ -612,7 +524,10 @@ int virHashForEach(virHashTablePtr table, virHashIterator iter, void *data)
  *
  * Returns number of items removed on success, -1 on failure
  */
-int virHashRemoveSet(virHashTablePtr table, virHashSearcher iter, const void *data) {
+int virHashRemoveSet(virHashTablePtr table,
+                     virHashSearcher iter,
+                     const void *data)
+{
     int i, count = 0;
 
     if (table == NULL || iter == NULL)
@@ -624,44 +539,27 @@ int virHashRemoveSet(virHashTablePtr table, virHashSearcher iter, const void *da
     table->iterating = true;
     table->current = NULL;
     for (i = 0 ; i < table->size ; i++) {
-        virHashEntryPtr prev = NULL;
-        virHashEntryPtr entry = &(table->table[i]);
+        virHashEntryPtr *nextptr = table->table + i;
 
-        while (entry && entry->valid) {
-            if (iter(entry->payload, entry->name, data)) {
+        while (*nextptr) {
+            virHashEntryPtr entry = *nextptr;
+            if (!iter(entry->payload, entry->name, data)) {
+                *nextptr = entry->next;
+            } else {
                 count++;
                 if (table->dataFree)
                     table->dataFree(entry->payload, entry->name);
                 if (table->keyFree)
                     table->keyFree(entry->name);
+                *nextptr = entry->next;
+                VIR_FREE(entry);
                 table->nbElems--;
-                if (prev) {
-                    prev->next = entry->next;
-                    VIR_FREE(entry);
-                    entry = prev;
-                } else {
-                    if (entry->next == NULL) {
-                        entry->valid = 0;
-                        entry->name = NULL;
-                    } else {
-                        entry = entry->next;
-                        memcpy(&(table->table[i]), entry,
-                               sizeof(virHashEntry));
-                        VIR_FREE(entry);
-                        entry = &(table->table[i]);
-                        continue;
-                    }
-                }
-            }
-            prev = entry;
-            if (entry) {
-                entry = entry->next;
             }
         }
     }
     table->iterating = false;
 
-    return (count);
+    return count;
 }
 
 /**
@@ -675,7 +573,10 @@ int virHashRemoveSet(virHashTablePtr table, virHashSearcher iter, const void *da
  * returns non-zero will be returned by this function.
  * The elements are processed in a undefined order
  */
-void *virHashSearch(virHashTablePtr table, virHashSearcher iter, const void *data) {
+void *virHashSearch(virHashTablePtr table,
+                    virHashSearcher iter,
+                    const void *data)
+{
     int i;
 
     if (table == NULL || iter == NULL)
@@ -687,18 +588,15 @@ void *virHashSearch(virHashTablePtr table, virHashSearcher iter, const void *dat
     table->iterating = true;
     table->current = NULL;
     for (i = 0 ; i < table->size ; i++) {
-        virHashEntryPtr entry = table->table + i;
-        while (entry) {
-            if (entry->valid) {
-                if (iter(entry->payload, entry->name, data)) {
-                    table->iterating = false;
-                    return entry->payload;
-                }
+        virHashEntryPtr entry;
+        for (entry = table->table[i]; entry; entry = entry->next) {
+            if (iter(entry->payload, entry->name, data)) {
+                table->iterating = false;
+                return entry->payload;
             }
-            entry = entry->next;
         }
     }
     table->iterating = false;
 
-    return (NULL);
+    return NULL;
 }
-- 
1.7.5.rc1


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