Wed Oct 28 15:47:49 2009

Asterisk developer's documentation

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astobj2.c

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/*
 * astobj2 - replacement containers for asterisk data structures.
 *
 * Copyright (C) 2006 Marta Carbone, Luigi Rizzo - Univ. di Pisa, Italy
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 */

/*
 * Function implementing astobj2 objects.
 */
#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 215958 $")

#include <stdlib.h>

#include "asterisk/astobj2.h"
#include "asterisk/utils.h"
#include "asterisk/cli.h"
#include "asterisk/linkedlists.h"

/*!
 * astobj2 objects are always prepended this data structure,
 * which contains a lock, a reference counter,
 * the flags and a pointer to a destructor.
 * The refcount is used to decide when it is time to
 * invoke the destructor.
 * The magic number is used for consistency check.
 * XXX the lock is not always needed, and its initialization may be
 * expensive. Consider making it external.
 */
struct __priv_data {
   ast_mutex_t lock;
   int ref_counter;
   ao2_destructor_fn destructor_fn;
   /*! for stats */
   size_t data_size;
   /*! magic number.  This is used to verify that a pointer passed in is a
    *  valid astobj2 */
   uint32_t magic;
};

#define  AO2_MAGIC   0xa570b123

/*!
 * What an astobj2 object looks like: fixed-size private data
 * followed by variable-size user data.
 */
struct astobj2 {
   struct __priv_data priv_data;
   void *user_data[0];
};

#ifdef AST_DEVMODE
#define AO2_DEBUG 1
#endif

#ifdef AO2_DEBUG
struct ao2_stats {
   volatile int total_objects;
   volatile int total_mem;
   volatile int total_containers;
   volatile int total_refs;
   volatile int total_locked;
};

static struct ao2_stats ao2;
#endif

#ifndef HAVE_BKTR /* backtrace support */
void ao2_bt(void) {}
#else
#include <execinfo.h>    /* for backtrace */

void ao2_bt(void)
{
    int c, i;
#define N1  20
    void *addresses[N1];
    char **strings;

    c = backtrace(addresses, N1);
    strings = backtrace_symbols(addresses,c);
    ast_verbose("backtrace returned: %d\n", c);
    for(i = 0; i < c; i++) {
        ast_verbose("%d: %p %s\n", i, addresses[i], strings[i]);
    }
    free(strings);
}
#endif

/*!
 * \brief convert from a pointer _p to a user-defined object
 *
 * \return the pointer to the astobj2 structure
 */
static inline struct astobj2 *INTERNAL_OBJ(void *user_data)
{
   struct astobj2 *p;

   if (!user_data) {
      ast_log(LOG_ERROR, "user_data is NULL\n");
      return NULL;
   }

   p = (struct astobj2 *) ((char *) user_data - sizeof(*p));
   if (AO2_MAGIC != (p->priv_data.magic) ) {
      ast_log(LOG_ERROR, "bad magic number 0x%x for %p\n", p->priv_data.magic, p);
      p = NULL;
   }

   return p;
}

/*!
 * \brief convert from a pointer _p to an astobj2 object
 *
 * \return the pointer to the user-defined portion.
 */
#define EXTERNAL_OBJ(_p)   ((_p) == NULL ? NULL : (_p)->user_data)

int ao2_lock(void *user_data)
{
   struct astobj2 *p = INTERNAL_OBJ(user_data);

   if (p == NULL)
      return -1;

#ifdef AO2_DEBUG
   ast_atomic_fetchadd_int(&ao2.total_locked, 1);
#endif

   return ast_mutex_lock(&p->priv_data.lock);
}

int ao2_unlock(void *user_data)
{
   struct astobj2 *p = INTERNAL_OBJ(user_data);

   if (p == NULL)
      return -1;

#ifdef AO2_DEBUG
   ast_atomic_fetchadd_int(&ao2.total_locked, -1);
#endif

   return ast_mutex_unlock(&p->priv_data.lock);
}

/*
 * The argument is a pointer to the user portion.
 */
int ao2_ref(void *user_data, const int delta)
{
   int current_value;
   int ret;
   struct astobj2 *obj = INTERNAL_OBJ(user_data);

   if (obj == NULL)
      return -1;

   /* if delta is 0, just return the refcount */
   if (delta == 0)
      return (obj->priv_data.ref_counter);

   /* we modify with an atomic operation the reference counter */
   ret = ast_atomic_fetchadd_int(&obj->priv_data.ref_counter, delta);
   current_value = ret + delta;

#ifdef AO2_DEBUG  
   ast_atomic_fetchadd_int(&ao2.total_refs, delta);
#endif

   /* this case must never happen */
   if (current_value < 0)
      ast_log(LOG_ERROR, "refcount %d on object %p\n", current_value, user_data);

   if (current_value <= 0) { /* last reference, destroy the object */
      if (obj->priv_data.destructor_fn != NULL) 
         obj->priv_data.destructor_fn(user_data);

      ast_mutex_destroy(&obj->priv_data.lock);
#ifdef AO2_DEBUG
      ast_atomic_fetchadd_int(&ao2.total_mem, - obj->priv_data.data_size);
      ast_atomic_fetchadd_int(&ao2.total_objects, -1);
#endif
      /* for safety, zero-out the astobj2 header and also the
       * first word of the user-data, which we make sure is always
       * allocated. */
      bzero(obj, sizeof(struct astobj2 *) + sizeof(void *) );
      free(obj);
   }

   return ret;
}

/*
 * We always alloc at least the size of a void *,
 * for debugging purposes.
 */
void *ao2_alloc(size_t data_size, ao2_destructor_fn destructor_fn)
{
   /* allocation */
   struct astobj2 *obj;

   if (data_size < sizeof(void *))
      data_size = sizeof(void *);

   obj = calloc(1, sizeof(*obj) + data_size);

   if (obj == NULL)
      return NULL;

   ast_mutex_init(&obj->priv_data.lock);
   obj->priv_data.magic = AO2_MAGIC;
   obj->priv_data.data_size = data_size;
   obj->priv_data.ref_counter = 1;
   obj->priv_data.destructor_fn = destructor_fn;   /* can be NULL */

#ifdef AO2_DEBUG
   ast_atomic_fetchadd_int(&ao2.total_objects, 1);
   ast_atomic_fetchadd_int(&ao2.total_mem, data_size);
   ast_atomic_fetchadd_int(&ao2.total_refs, 1);
#endif

   /* return a pointer to the user data */
   return EXTERNAL_OBJ(obj);
}

/* internal callback to destroy a container. */
static void container_destruct(void *c);

/* each bucket in the container is a tailq. */
AST_LIST_HEAD_NOLOCK(bucket, bucket_list);

/*!
 * A container; stores the hash and callback functions, information on
 * the size, the hash bucket heads, and a version number, starting at 0
 * (for a newly created, empty container)
 * and incremented every time an object is inserted or deleted.
 * The assumption is that an object is never moved in a container,
 * but removed and readded with the new number.
 * The version number is especially useful when implementing iterators.
 * In fact, we can associate a unique, monotonically increasing number to
 * each object, which means that, within an iterator, we can store the
 * version number of the current object, and easily look for the next one,
 * which is the next one in the list with a higher number.
 * Since all objects have a version >0, we can use 0 as a marker for
 * 'we need the first object in the bucket'.
 *
 * \todo Linking and unlink objects is typically expensive, as it
 * involves a malloc() of a small object which is very inefficient.
 * To optimize this, we allocate larger arrays of bucket_list's
 * when we run out of them, and then manage our own freelist.
 * This will be more efficient as we can do the freelist management while
 * we hold the lock (that we need anyways).
 */
struct ao2_container {
   ao2_hash_fn hash_fn;
   ao2_callback_fn cmp_fn;
   int n_buckets;
   /*! Number of elements in the container */
   int elements;
   /*! described above */
   int version;
   /*! variable size */
   struct bucket buckets[0];
};
 
/*!
 * \brief always zero hash function
 *
 * it is convenient to have a hash function that always returns 0.
 * This is basically used when we want to have a container that is
 * a simple linked list.
 *
 * \returns 0
 */
static int hash_zero(const void *user_obj, const int flags)
{
   return 0;
}

/*
 * A container is just an object, after all!
 */
struct ao2_container *
ao2_container_alloc(const unsigned int n_buckets, ao2_hash_fn hash_fn,
      ao2_callback_fn cmp_fn)
{
   /* XXX maybe consistency check on arguments ? */
   /* compute the container size */
   size_t container_size = sizeof(struct ao2_container) + n_buckets * sizeof(struct bucket);

   struct ao2_container *c = ao2_alloc(container_size, container_destruct);

   if (!c)
      return NULL;
   
   c->version = 1;   /* 0 is a reserved value here */
   c->n_buckets = n_buckets;
   c->hash_fn = hash_fn ? hash_fn : hash_zero;
   c->cmp_fn = cmp_fn;

#ifdef AO2_DEBUG
   ast_atomic_fetchadd_int(&ao2.total_containers, 1);
#endif

   return c;
}

/*!
 * return the number of elements in the container
 */
int ao2_container_count(struct ao2_container *c)
{
   return c->elements;
}

/*!
 * A structure to create a linked list of entries,
 * used within a bucket.
 * XXX \todo this should be private to the container code
 */
struct bucket_list {
   AST_LIST_ENTRY(bucket_list) entry;
   int version;
   struct astobj2 *astobj;    /* pointer to internal data */
}; 

/*
 * link an object to a container
 */
void *__ao2_link(struct ao2_container *c, void *user_data, int iax2_hack)
{
   int i;
   /* create a new list entry */
   struct bucket_list *p;
   struct astobj2 *obj = INTERNAL_OBJ(user_data);
   
   if (!obj)
      return NULL;

   if (INTERNAL_OBJ(c) == NULL)
      return NULL;

   p = calloc(1, sizeof(*p));
   if (!p)
      return NULL;

   i = c->hash_fn(user_data, OBJ_POINTER);

   ao2_lock(c);
   i %= c->n_buckets;
   p->astobj = obj;
   p->version = ast_atomic_fetchadd_int(&c->version, 1);
   if (iax2_hack)
      AST_LIST_INSERT_HEAD(&c->buckets[i], p, entry);
   else
      AST_LIST_INSERT_TAIL(&c->buckets[i], p, entry);
   ast_atomic_fetchadd_int(&c->elements, 1);
   ao2_ref(user_data, +1);
   ao2_unlock(c);
   
   return p;
}

/*!
 * \brief another convenience function is a callback that matches on address
 */
int ao2_match_by_addr(void *user_data, void *arg, int flags)
{
   return (user_data == arg) ? (CMP_MATCH | CMP_STOP) : 0;
}

/*
 * Unlink an object from the container
 * and destroy the associated * ao2_bucket_list structure.
 */
void *ao2_unlink(struct ao2_container *c, void *user_data)
{
   if (INTERNAL_OBJ(user_data) == NULL)   /* safety check on the argument */
      return NULL;

   ao2_callback(c, OBJ_UNLINK | OBJ_POINTER | OBJ_NODATA, ao2_match_by_addr, user_data);

   return NULL;
}

/*! 
 * \brief special callback that matches all 
 */ 
static int cb_true(void *user_data, void *arg, int flags)
{
   return CMP_MATCH;
}

/*!
 * Browse the container using different stategies accoding the flags.
 * \return Is a pointer to an object or to a list of object if OBJ_MULTIPLE is 
 * specified.
 */
void *ao2_callback(struct ao2_container *c,
   const enum search_flags flags,
   ao2_callback_fn cb_fn, void *arg)
{
   int i, start, last;  /* search boundaries */
   void *ret = NULL;

   if (INTERNAL_OBJ(c) == NULL)  /* safety check on the argument */
      return NULL;

   if ((flags & (OBJ_MULTIPLE | OBJ_NODATA)) == OBJ_MULTIPLE) {
      ast_log(LOG_WARNING, "multiple data return not implemented yet (flags %x)\n", flags);
      return NULL;
   }

   /* override the match function if necessary */
#if 0
   /* Removing this slightly changes the meaning of OBJ_POINTER, but makes it
    * do what I want it to.  I'd like to hint to ao2_callback that the arg is
    * of the same object type, so it can be passed to the hash function.
    * However, I don't want to imply that this is the object being searched for. */
   if (flags & OBJ_POINTER)
      cb_fn = match_by_addr;
   else
#endif
   if (cb_fn == NULL)   /* if NULL, match everything */
      cb_fn = cb_true;
   /*
    * XXX this can be optimized.
    * If we have a hash function and lookup by pointer,
    * run the hash function. Otherwise, scan the whole container
    * (this only for the time being. We need to optimize this.)
    */
   if ((flags & OBJ_POINTER)) /* we know hash can handle this case */
      start = i = c->hash_fn(arg, flags & OBJ_POINTER) % c->n_buckets;
   else        /* don't know, let's scan all buckets */
      i = -1;     /* XXX this must be fixed later. */

   /* determine the search boundaries: i..last-1 */
   if (i < 0) {
      start = i = 0;
      last = c->n_buckets;
   } else if ((flags & OBJ_CONTINUE)) {
      last = c->n_buckets;
   } else {
      last = i + 1;
   }

   ao2_lock(c);   /* avoid modifications to the content */

   for (; i < last ; i++) {
      /* scan the list with prev-cur pointers */
      struct bucket_list *cur;

      AST_LIST_TRAVERSE_SAFE_BEGIN(&c->buckets[i], cur, entry) {
         int match = cb_fn(EXTERNAL_OBJ(cur->astobj), arg, flags) & (CMP_MATCH | CMP_STOP);

         /* we found the object, performing operations according flags */
         if (match == 0) { /* no match, no stop, continue */
            continue;
         } else if (match == CMP_STOP) {  /* no match but stop, we are done */
            i = last;
            break;
         }
         /* we have a match (CMP_MATCH) here */
         if (!(flags & OBJ_NODATA)) {  /* if must return the object, record the value */
            /* it is important to handle this case before the unlink */
            ret = EXTERNAL_OBJ(cur->astobj);
            ao2_ref(ret, 1);
         }

         if (flags & OBJ_UNLINK) {  /* must unlink */
            struct bucket_list *x = cur;

            /* we are going to modify the container, so update version */
            ast_atomic_fetchadd_int(&c->version, 1);
            AST_LIST_REMOVE_CURRENT(&c->buckets[i], entry);
            /* update number of elements and version */
            ast_atomic_fetchadd_int(&c->elements, -1);
            ao2_ref(EXTERNAL_OBJ(x->astobj), -1);
            free(x); /* free the link record */
         }

         if ((match & CMP_STOP) || (flags & OBJ_MULTIPLE) == 0) {
            /* We found the only match we need */
            i = last;   /* force exit from outer loop */
            break;
         }
         if (!(flags & OBJ_NODATA)) {
#if 0 /* XXX to be completed */
            /*
             * This is the multiple-return case. We need to link
             * the object in a list. The refcount is already increased.
             */
#endif
         }
      }
      AST_LIST_TRAVERSE_SAFE_END

      if (ret) {
         /* This assumes OBJ_MULTIPLE with !OBJ_NODATA is still not implemented */
         break;
      }

      if (i == c->n_buckets - 1 && (flags & OBJ_POINTER) && (flags & OBJ_CONTINUE)) {
         /* Move to the beginning to ensure we check every bucket */
         i = -1;
         last = start;
      }
   }
   ao2_unlock(c);
   return ret;
}

/*!
 * the find function just invokes the default callback with some reasonable flags.
 */
void *ao2_find(struct ao2_container *c, void *arg, enum search_flags flags)
{
   return ao2_callback(c, flags, c->cmp_fn, arg);
}

/*!
 * initialize an iterator so we start from the first object
 */
struct ao2_iterator ao2_iterator_init(struct ao2_container *c, int flags)
{
   struct ao2_iterator a = {
      .c = c,
      .flags = flags
   };
   
   return a;
}

/*
 * move to the next element in the container.
 */
void * ao2_iterator_next(struct ao2_iterator *a)
{
   int lim;
   struct bucket_list *p = NULL;
   void *ret = NULL;

   if (INTERNAL_OBJ(a->c) == NULL)
      return NULL;

   if (!(a->flags & F_AO2I_DONTLOCK))
      ao2_lock(a->c);

   /* optimization. If the container is unchanged and
    * we have a pointer, try follow it
    */
   if (a->c->version == a->c_version && (p = a->obj) ) {
      if ( (p = AST_LIST_NEXT(p, entry)) )
         goto found;
      /* nope, start from the next bucket */
      a->bucket++;
      a->version = 0;
      a->obj = NULL;
   }

   lim = a->c->n_buckets;

   /* Browse the buckets array, moving to the next
    * buckets if we don't find the entry in the current one.
    * Stop when we find an element with version number greater
    * than the current one (we reset the version to 0 when we
    * switch buckets).
    */
   for (; a->bucket < lim; a->bucket++, a->version = 0) {
      /* scan the current bucket */
      AST_LIST_TRAVERSE(&a->c->buckets[a->bucket], p, entry) {
         if (p->version > a->version)
            goto found;
      }
   }

found:
   if (p) {
      a->version = p->version;
      a->obj = p;
      a->c_version = a->c->version;
      ret = EXTERNAL_OBJ(p->astobj);
      /* inc refcount of returned object */
      ao2_ref(ret, 1);
   }

   if (!(a->flags & F_AO2I_DONTLOCK))
      ao2_unlock(a->c);

   return ret;
}

/* callback for destroying container.
 * we can make it simple as we know what it does
 */
static int cd_cb(void *obj, void *arg, int flag)
{
   ao2_ref(obj, -1);
   return 0;
}
   
static void container_destruct(void *_c)
{
   struct ao2_container *c = _c;

   ao2_callback(c, OBJ_UNLINK, cd_cb, NULL);

#ifdef AO2_DEBUG
   ast_atomic_fetchadd_int(&ao2.total_containers, -1);
#endif
}

#ifdef AO2_DEBUG
static int print_cb(void *obj, void *arg, int flag)
{
   int *fd = arg;
   char *s = (char *)obj;

   ast_cli(*fd, "string <%s>\n", s);
   return 0;
}

/*
 * Print stats
 */
static int handle_astobj2_stats(int fd, int argc, char *argv[])
{
   ast_cli(fd, "Objects    : %d\n", ao2.total_objects);
   ast_cli(fd, "Containers : %d\n", ao2.total_containers);
   ast_cli(fd, "Memory     : %d\n", ao2.total_mem);
   ast_cli(fd, "Locked     : %d\n", ao2.total_locked);
   ast_cli(fd, "Refs       : %d\n", ao2.total_refs);
   return 0;
}

/*
 * This is testing code for astobj
 */
static int handle_astobj2_test(int fd, int argc, char *argv[])
{
   struct ao2_container *c1;
   int i, lim;
   char *obj;
   static int prof_id = -1;

   if (prof_id == -1)
      prof_id = ast_add_profile("ao2_alloc", 0);

   ast_cli(fd, "argc %d argv %s %s %s\n", argc, argv[0], argv[1], argv[2]);
   lim = atoi(argv[2]);
   ast_cli(fd, "called astobj_test\n");

   handle_astobj2_stats(fd, 0, NULL);
   /*
    * allocate a container with no default callback, and no hash function.
    * No hash means everything goes in the same bucket.
    */
   c1 = ao2_container_alloc(100, NULL /* no callback */, NULL /* no hash */);
   ast_cli(fd, "container allocated as %p\n", c1);

   /*
    * fill the container with objects.
    * ao2_alloc() gives us a reference which we pass to the
    * container when we do the insert.
    */
   for (i = 0; i < lim; i++) {
      ast_mark(prof_id, 1 /* start */);
      obj = ao2_alloc(80, NULL);
      ast_mark(prof_id, 0 /* stop */);
      ast_cli(fd, "object %d allocated as %p\n", i, obj);
      sprintf(obj, "-- this is obj %d --", i);
      ao2_link(c1, obj);
   }
   ast_cli(fd, "testing callbacks\n");
   ao2_callback(c1, 0, print_cb, &fd);

   ast_cli(fd, "testing iterators, remove every second object\n");
   {
      struct ao2_iterator ai;
      int x = 0;

      ai = ao2_iterator_init(c1, 0);
      while ( (obj = ao2_iterator_next(&ai)) ) {
         ast_cli(fd, "iterator on <%s>\n", obj);
         if (x++ & 1)
            ao2_unlink(c1, obj);
         ao2_ref(obj, -1);
      }
      ast_cli(fd, "testing iterators again\n");
      ai = ao2_iterator_init(c1, 0);
      while ( (obj = ao2_iterator_next(&ai)) ) {
         ast_cli(fd, "iterator on <%s>\n", obj);
         ao2_ref(obj, -1);
      }
   }
   ast_cli(fd, "testing callbacks again\n");
   ao2_callback(c1, 0, print_cb, &fd);

   ast_verbose("now you should see an error message:\n");
   ao2_ref(&i, -1);  /* i is not a valid object so we print an error here */

   ast_cli(fd, "destroy container\n");
   ao2_ref(c1, -1);  /* destroy container */
   handle_astobj2_stats(fd, 0, NULL);
   return 0;
}

static struct ast_cli_entry cli_astobj2[] = {
   { { "astobj2", "stats", NULL },
   handle_astobj2_stats, "Print astobj2 statistics", },
   { { "astobj2", "test", NULL } , handle_astobj2_test, "Test astobj2", },
};
#endif /* AO2_DEBUG */

int astobj2_init(void)
{
#ifdef AO2_DEBUG
   ast_cli_register_multiple(cli_astobj2, ARRAY_LEN(cli_astobj2));
#endif

   return 0;
}

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