hash.c

/**
 * \file hash.c
 * Generic hash table. 
 *
 * Used for display lists, texture objects, vertex/fragment programs,
 * buffer objects, etc.  The hash functions are thread-safe.
 * 
 * \note key=0 is illegal.
 *
 * \author Brian Paul
 */

/*
 * Mesa 3-D graphics library
 * Version:  6.4
 *
 * Copyright (C) 1999-2005  Brian Paul   All Rights Reserved.
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * BRIAN PAUL BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
 * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 */


#include "glheader.h"
#include "imports.h"
#include "glthread.h"
#include "hash.h"


#define TABLE_SIZE 1023  /**< Size of lookup table/array */

#define HASH_FUNC(K)  ((K) % TABLE_SIZE)


/**
 * An entry in the hash table.  
 *
 * This struct is private to this file.
 */
struct HashEntry {
   GLuint Key;             /**< the entry's key */
   void *Data;             /**< the entry's data */
   struct HashEntry *Next; /**< pointer to next entry */
};

/**
 * The hash table data structure.  
 *
 * This is an opaque types (it's not defined in hash.h file).
 */
struct _mesa_HashTable {
   struct HashEntry *Table[TABLE_SIZE];  /**< the lookup table */
   GLuint MaxKey;                        /**< highest key inserted so far */
   _glthread_Mutex Mutex;                /**< mutual exclusion lock */
};


/**
 * Create a new hash table.
 * 
 * \return pointer to a new, empty hash table.
 */
struct _mesa_HashTable *
_mesa_NewHashTable(void)
{
   struct _mesa_HashTable *table = CALLOC_STRUCT(_mesa_HashTable);
   if (table) {
      _glthread_INIT_MUTEX(table->Mutex);
   }
   return table;
}



/**
 * Delete a hash table.
 * Frees each entry on the hash table and then the hash table structure itself.
 * Note that the caller should have already traversed the table and deleted
 * the objects in the table (i.e. We don't free the entries' data pointer).
 *
 * \param table the hash table to delete.
 */
void
_mesa_DeleteHashTable(struct _mesa_HashTable *table)
{
   GLuint i;
   assert(table);
   for (i = 0; i < TABLE_SIZE; i++) {
      struct HashEntry *entry = table->Table[i];
      while (entry) {
	 struct HashEntry *next = entry->Next;
	 FREE(entry);
	 entry = next;
      }
   }
   _glthread_DESTROY_MUTEX(table->Mutex);
   FREE(table);
}



/**
 * Lookup an entry in the hash table.
 * 
 * \param table the hash table.
 * \param key the key.
 * 
 * \return pointer to user's data or NULL if key not in table
 */
void *
_mesa_HashLookup(const struct _mesa_HashTable *table, GLuint key)
{
   GLuint pos;
   const struct HashEntry *entry;

   assert(table);
   assert(key);

   pos = HASH_FUNC(key);
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
	 return entry->Data;
      }
      entry = entry->Next;
   }
   return NULL;
}



/**
 * Insert a key/pointer pair into the hash table.  
 * If an entry with this key already exists we'll replace the existing entry.
 * 
 * \param table the hash table.
 * \param key the key (not zero).
 * \param data pointer to user data.
 */
void
_mesa_HashInsert(struct _mesa_HashTable *table, GLuint key, void *data)
{
   /* search for existing entry with this key */
   GLuint pos;
   struct HashEntry *entry;

   assert(table);
   assert(key);

   _glthread_LOCK_MUTEX(table->Mutex);

   if (key > table->MaxKey)
      table->MaxKey = key;

   pos = HASH_FUNC(key);
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
         /* replace entry's data */
	 entry->Data = data;
         _glthread_UNLOCK_MUTEX(table->Mutex);
	 return;
      }
      entry = entry->Next;
   }

   /* alloc and insert new table entry */
   entry = MALLOC_STRUCT(HashEntry);
   entry->Key = key;
   entry->Data = data;
   entry->Next = table->Table[pos];
   table->Table[pos] = entry;

   _glthread_UNLOCK_MUTEX(table->Mutex);
}



/**
 * Remove an entry from the hash table.
 * 
 * \param table the hash table.
 * \param key key of entry to remove.
 *
 * While holding the hash table's lock, searches the entry with the matching
 * key and unlinks it.
 */
void
_mesa_HashRemove(struct _mesa_HashTable *table, GLuint key)
{
   GLuint pos;
   struct HashEntry *entry, *prev;

   assert(table);
   assert(key);

   _glthread_LOCK_MUTEX(table->Mutex);

   pos = HASH_FUNC(key);
   prev = NULL;
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
         /* found it! */
         if (prev) {
            prev->Next = entry->Next;
         }
         else {
            table->Table[pos] = entry->Next;
         }
         FREE(entry);
         _glthread_UNLOCK_MUTEX(table->Mutex);
	 return;
      }
      prev = entry;
      entry = entry->Next;
   }

   _glthread_UNLOCK_MUTEX(table->Mutex);
}



/**
 * Get the key of the "first" entry in the hash table.
 * 
 * This is used in the course of deleting all display lists when
 * a context is destroyed.
 * 
 * \param table the hash table
 * 
 * \return key for the "first" entry in the hash table.
 *
 * While holding the lock, walks through all table positions until finding
 * the first entry of the first non-empty one.
 */
GLuint
_mesa_HashFirstEntry(struct _mesa_HashTable *table)
{
   GLuint pos;
   assert(table);
   _glthread_LOCK_MUTEX(table->Mutex);
   for (pos=0; pos < TABLE_SIZE; pos++) {
      if (table->Table[pos]) {
         _glthread_UNLOCK_MUTEX(table->Mutex);
         return table->Table[pos]->Key;
      }
   }
   _glthread_UNLOCK_MUTEX(table->Mutex);
   return 0;
}


/**
 * Given a hash table key, return the next key.  This is used to walk
 * over all entries in the table.  Note that the keys returned during
 * walking won't be in any particular order.
 * \return next hash key or 0 if end of table.
 */
GLuint
_mesa_HashNextEntry(const struct _mesa_HashTable *table, GLuint key)
{
   const struct HashEntry *entry;
   GLuint pos;

   assert(table);
   assert(key);

   /* Find the entry with given key */
   pos = HASH_FUNC(key);
   entry = table->Table[pos];
   while (entry) {
      if (entry->Key == key) {
         break;
      }
      entry = entry->Next;
   }

   if (!entry) {
      /* the key was not found, we can't find next entry */
      return 0;
   }

   if (entry->Next) {
      /* return next in linked list */
      return entry->Next->Key;
   }
   else {
      /* look for next non-empty table slot */
      pos++;
      while (pos < TABLE_SIZE) {
         if (table->Table[pos]) {
            return table->Table[pos]->Key;
         }
         pos++;
      }
      return 0;
   }
}


/**
 * Dump contents of hash table for debugging.
 * 
 * \param table the hash table.
 */
void
_mesa_HashPrint(const struct _mesa_HashTable *table)
{
   GLuint i;
   assert(table);
   for (i=0;i<TABLE_SIZE;i++) {
      const struct HashEntry *entry = table->Table[i];
      while (entry) {
	 _mesa_debug(NULL, "%u %p\n", entry->Key, entry->Data);
	 entry = entry->Next;
      }
   }
}



/**
 * Find a block of adjacent unused hash keys.
 * 
 * \param table the hash table.
 * \param numKeys number of keys needed.
 * 
 * \return Starting key of free block or 0 if failure.
 *
 * If there are enough free keys between the maximum key existing in the table
 * (_mesa_HashTable::MaxKey) and the maximum key possible, then simply return
 * the adjacent key. Otherwise do a full search for a free key block in the
 * allowable key range.
 */
GLuint
_mesa_HashFindFreeKeyBlock(struct _mesa_HashTable *table, GLuint numKeys)
{
   GLuint maxKey = ~((GLuint) 0);
   _glthread_LOCK_MUTEX(table->Mutex);
   if (maxKey - numKeys > table->MaxKey) {
      /* the quick solution */
      _glthread_UNLOCK_MUTEX(table->Mutex);
      return table->MaxKey + 1;
   }
   else {
      /* the slow solution */
      GLuint freeCount = 0;
      GLuint freeStart = 1;
      GLuint key;
      for (key=1; key!=maxKey; key++) {
	 if (_mesa_HashLookup(table, key)) {
	    /* darn, this key is already in use */
	    freeCount = 0;
	    freeStart = key+1;
	 }
	 else {
	    /* this key not in use, check if we've found enough */
	    freeCount++;
	    if (freeCount == numKeys) {
               _glthread_UNLOCK_MUTEX(table->Mutex);
	       return freeStart;
	    }
	 }
      }
      /* cannot allocate a block of numKeys consecutive keys */
      _glthread_UNLOCK_MUTEX(table->Mutex);
      return 0;
   }
}


#if 0 /* debug only */

/**
 * Test walking over all the entries in a hash table.
 */
static void
test_hash_walking(void)
{
   struct _mesa_HashTable *t = _mesa_NewHashTable();
   const GLuint limit = 50000;
   GLuint i;

   /* create some entries */
   for (i = 0; i < limit; i++) {
      GLuint dummy;
      GLuint k = (rand() % (limit * 10)) + 1;
      while (_mesa_HashLookup(t, k)) {
         /* id already in use, try another */
         k = (rand() % (limit * 10)) + 1;
      }
      _mesa_HashInsert(t, k, &dummy);
   }

   /* walk over all entries */
   {
      GLuint k = _mesa_HashFirstEntry(t);
      GLuint count = 0;
      while (k) {
         GLuint knext = _mesa_HashNextEntry(t, k);
         assert(knext != k);
         _mesa_HashRemove(t, k);
         count++;
         k = knext;
      }
      assert(count == limit);
      k = _mesa_HashFirstEntry(t);
      assert(k==0);
   }

   _mesa_DeleteHashTable(t);
}


void
_mesa_test_hash_functions(void)
{
   int a, b, c;
   struct _mesa_HashTable *t;

   t = _mesa_NewHashTable();
   _mesa_HashInsert(t, 501, &a);
   _mesa_HashInsert(t, 10, &c);
   _mesa_HashInsert(t, 0xfffffff8, &b);
   /*_mesa_HashPrint(t);*/

   assert(_mesa_HashLookup(t,501));
   assert(!_mesa_HashLookup(t,1313));
   assert(_mesa_HashFindFreeKeyBlock(t, 100));

   _mesa_DeleteHashTable(t);

   test_hash_walking();
}

#endif