/src/freeradius-server/src/lib/server/pool.c

Source
/*
 *   This program is free software; you can redistribute it and/or modify
 *   it under the terms of the GNU General Public License as published by
 *   the Free Software Foundation; either version 2 of the License, or
 *   (at your option) any later version.
 *
 *   This program is distributed in the hope that it will be useful,
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *   GNU General Public License for more details.
 *
 *   You should have received a copy of the GNU General Public License
 *   along with this program; if not, write to the Free Software
 *   Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA
 */

/**
 * @file pool.c
 * @brief Handle pools of connections (threads, sockets, etc.)
 * @note This API must be used by all modules in the public distribution that
 * maintain pools of connections.
 *
 * @copyright 2012 The FreeRADIUS server project
 * @copyright 2012 Alan DeKok (aland@deployingradius.com)
 */
RCSID("$Id: 185e43b6f392295097c6327b91955835522520ad $")

#define LOG_PREFIX pool->log_prefix

#include <freeradius-devel/server/main_config.h>
#include <freeradius-devel/server/modpriv.h>
#include <freeradius-devel/server/trigger.h>

#include <freeradius-devel/util/debug.h>

#include <freeradius-devel/util/misc.h>


typedef struct fr_pool_connection_s fr_pool_connection_t;

static int connection_check(fr_pool_t *pool, request_t *request);
static int max_dflt(CONF_PAIR **out, void *parent, CONF_SECTION *cs, fr_token_t quote, conf_parser_t const *rule);

/** An individual connection within the connection pool
 *
 * Defines connection counters, timestamps, and holds a pointer to the
 * connection handle itself.
 *
 * @see fr_pool_t
 */
struct fr_pool_connection_s {
  fr_pool_connection_t  *prev;      //!< Previous connection in list.
  fr_pool_connection_t  *next;      //!< Next connection in list.
  fr_heap_index_t heap_id;      //!< For the next connection heap.

  fr_time_t created;    //!< Time connection was created.
  fr_time_t last_reserved;    //!< Last time the connection was reserved.

  fr_time_t last_released;    //!< Time the connection was released.

  uint32_t  num_uses;   //!< Number of times the connection has been reserved.
  uint64_t  number;     //!< Unique ID assigned when the connection is created,
            //!< these will monotonically increase over the
            //!< lifetime of the connection pool.
  void    *connection;    //!< Pointer to whatever the module uses for a connection
            //!< handle.
  bool    in_use;     //!< Whether the connection is currently reserved.

  bool    needs_reconnecting; //!< Reconnect this connection before use.

#ifdef PTHREAD_DEBUG
  pthread_t pthread_id;   //!< When 'in_use == true'.
#endif
};

/** A connection pool
 *
 * Defines the configuration of the connection pool, all the counters and
 * timestamps related to the connection pool, the mutex that stops multiple
 * threads leaving the pool in an inconsistent state, and the callbacks
 * required to open, close and check the status of connections within the pool.
 *
 * @see connection
 */
struct fr_pool_s {
  int   ref;      //!< Reference counter to prevent connection
            //!< pool being freed multiple times.
  uint32_t  start;      //!< Number of initial connections.
  uint32_t  min;      //!< Minimum number of concurrent connections to keep open.
  uint32_t  max;      //!< Maximum number of concurrent connections to allow.
  uint32_t  max_pending;    //!< Max number of pending connections to allow.
  uint32_t  spare;      //!< Number of spare connections to try.
  uint64_t  max_uses;   //!< Maximum number of times a connection can be used
            //!< before being closed.
  uint32_t  pending_window;   //!< Sliding window of pending connections.

  fr_time_delta_t retry_delay;    //!< seconds to delay re-open after a failed open.
  fr_time_delta_t cleanup_interval;   //!< Initial timer for how often we sweep the pool
            //!< for free connections. (0 is infinite).
  fr_time_delta_t delay_interval;   //!< When we next do a cleanup.  Initialized to
            //!< cleanup_interval, and increase from there based
            //!< on the delay.
  fr_time_delta_t lifetime;   //!< How long a connection can be open before being
            //!< closed (irrespective of whether it's idle or not).
  fr_time_delta_t idle_timeout;   //!< How long a connection can be idle before
            //!< being closed.
  fr_time_delta_t connect_timeout;  //!< New connection timeout, enforced by the create
            //!< callback.

  bool    spread;     //!< If true we spread requests over the connections,
            //!< using the connection released longest ago, first.

  fr_heap_t *heap;      //!< For the next connection heap

  fr_pool_connection_t  *head;    //!< Start of the connection list.
  fr_pool_connection_t  *tail;    //!< End of the connection list.

  pthread_mutex_t mutex;      //!< Mutex used to keep consistent state when making
            //!< modifications in threaded mode.
  pthread_cond_t  done_spawn;   //!< Threads that need to ensure no spawning is in progress,
            //!< should block on this condition if pending != 0.
  pthread_cond_t  done_reconnecting;  //!< Before calling the create callback, threads should
            //!< block on this condition if reconnecting == true.

  CONF_SECTION const *cs;     //!< Configuration section holding the section of parsed
            //!< config file that relates to this pool.
  void    *opaque;    //!< Pointer to context data that will be passed to callbacks.

  char const  *log_prefix;    //!< Log prefix to prepend to all log messages created
            //!< by the connection pool code.

  bool    triggers_enabled; //!< Whether we call the trigger functions.

  char const  *trigger_prefix;  //!< Prefix to prepend to names of all triggers
            //!< fired by the connection pool code.
  fr_pair_list_t  trigger_args;   //!< Arguments to make available in connection pool triggers.

  fr_time_delta_t held_trigger_min; //!< If a connection is held for less than the specified
            //!< period, fire a trigger.
  fr_time_delta_t held_trigger_max; //!< If a connection is held for longer than the specified
            //!< period, fire a trigger.

  fr_pool_connection_create_t create; //!< Function used to create new connections.
  fr_pool_connection_alive_t  alive;  //!< Function used to check status of connections.

  fr_pool_reconnect_t reconnect;  //!< Called during connection pool reconnect.

  fr_pool_state_t state;      //!< Stats and state of the connection pool.
};

static const conf_parser_t pool_config[] = {
  { FR_CONF_OFFSET("start", fr_pool_t, start), .dflt = "0" },
  { FR_CONF_OFFSET("min", fr_pool_t, min), .dflt = "0" },
  { FR_CONF_OFFSET("max", fr_pool_t, max), .dflt_func = max_dflt },
  { FR_CONF_OFFSET("max_pending", fr_pool_t, max_pending), .dflt = "0" },
  { FR_CONF_OFFSET("spare", fr_pool_t, spare), .dflt = "3" },
  { FR_CONF_OFFSET("uses", fr_pool_t, max_uses), .dflt = "0" },
  { FR_CONF_OFFSET("lifetime", fr_pool_t, lifetime), .dflt = "0" },
  { FR_CONF_OFFSET("cleanup_interval", fr_pool_t, cleanup_interval), .dflt = "30" },
  { FR_CONF_OFFSET("idle_timeout", fr_pool_t, idle_timeout), .dflt = "60" },
  { FR_CONF_OFFSET("connect_timeout", fr_pool_t, connect_timeout), .dflt = "3.0" },
  { FR_CONF_OFFSET("held_trigger_min", fr_pool_t, held_trigger_min), .dflt = "0.0" },
  { FR_CONF_OFFSET("held_trigger_max", fr_pool_t, held_trigger_max), .dflt = "0.5" },
  { FR_CONF_OFFSET("retry_delay", fr_pool_t, retry_delay), .dflt = "1" },
  { FR_CONF_OFFSET("spread", fr_pool_t, spread), .dflt = "no" },
  CONF_PARSER_TERMINATOR
};

static int max_dflt(CONF_PAIR **out, UNUSED void *parent, CONF_SECTION *cs, fr_token_t quote, conf_parser_t const *rule)
{
  char    *strvalue;

  strvalue = talloc_asprintf(NULL, "%u", main_config->max_workers);
  *out = cf_pair_alloc(cs, rule->name1, strvalue, T_OP_EQ, T_BARE_WORD, quote);
  talloc_free(strvalue);

  return 0;
}

/** Order connections by reserved most recently
 */
static int8_t last_reserved_cmp(void const *one, void const *two)
{
  fr_pool_connection_t const *a = one, *b = two;

  return fr_time_cmp(a->last_reserved, b->last_reserved);
}

/** Order connections by released longest ago
 */
static int8_t last_released_cmp(void const *one, void const *two)
{
  fr_pool_connection_t const *a = one, *b = two;

  return fr_time_cmp(a->last_released, b->last_released);
}

/** Removes a connection from the connection list
 *
 * @note Must be called with the mutex held.
 *
 * @param[in] pool  to modify.
 * @param[in] this  Connection to delete.
 */
static void connection_unlink(fr_pool_t *pool, fr_pool_connection_t *this)
{
  if (this->prev) {
    fr_assert(pool->head != this);
    this->prev->next = this->next;
  } else {
    fr_assert(pool->head == this);
    pool->head = this->next;
  }
  if (this->next) {
    fr_assert(pool->tail != this);
    this->next->prev = this->prev;
  } else {
    fr_assert(pool->tail == this);
    pool->tail = this->prev;
  }

  this->prev = this->next = NULL;
}

/** Adds a connection to the head of the connection list
 *
 * @note Must be called with the mutex held.
 *
 * @param[in] pool  to modify.
 * @param[in] this  Connection to add.
 */
static void connection_link_head(fr_pool_t *pool, fr_pool_connection_t *this)
{
  fr_assert(pool != NULL);
  fr_assert(this != NULL);
  fr_assert(pool->head != this);
  fr_assert(pool->tail != this);

  if (pool->head) {
    pool->head->prev = this;
  }

  this->next = pool->head;
  this->prev = NULL;
  pool->head = this;
  if (!pool->tail) {
    fr_assert(this->next == NULL);
    pool->tail = this;
  } else {
    fr_assert(this->next != NULL);
  }
}

/** Send a connection pool trigger.
 *
 * @param[in] pool  to send trigger for.
 * @param[in] event trigger name suffix.
 */
static inline void fr_pool_trigger(fr_pool_t *pool, char const *event)
{
  char  name[128];

  fr_assert(pool != NULL);
  fr_assert(event != NULL);

  if (!pool->triggers_enabled) return;

  snprintf(name, sizeof(name), "%s.%s", pool->trigger_prefix, event);
  trigger(unlang_interpret_get_thread_default(), pool->cs, NULL, name, true, &pool->trigger_args);
}

/** Find a connection handle in the connection list
 *
 * Walks over the list of connections searching for a specified connection
 * handle and returns the first connection that contains that pointer.
 *
 * @note Will lock mutex and only release mutex if connection handle
 * is not found, so will usually return will mutex held.
 * @note Must be called with the mutex free.
 *
 * @param[in] pool  to search in.
 * @param[in] conn  handle to search for.
 * @return
 *  - Connection containing the specified handle.
 *  - NULL if no such connection was found.
 */
static fr_pool_connection_t *connection_find(fr_pool_t *pool, void *conn)
{
  fr_pool_connection_t *this;

  if (!pool || !conn) return NULL;

  pthread_mutex_lock(&pool->mutex);

  /*
   *  FIXME: This loop could be avoided if we passed a 'void
   *  **connection' instead.  We could use "offsetof" in
   *  order to find top of the parent structure.
   */
  for (this = pool->head; this != NULL; this = this->next) {
    if (this->connection == conn) {
#ifdef PTHREAD_DEBUG
      pthread_t pthread_id;

      pthread_id = pthread_self();
      fr_assert(pthread_equal(this->pthread_id, pthread_id) != 0);
#endif

      fr_assert(this->in_use == true);
      return this;
    }
  }

  pthread_mutex_unlock(&pool->mutex);
  return NULL;
}

/** Spawns a new connection
 *
 * Spawns a new connection using the create callback, and returns it for
 * adding to the connection list.
 *
 * @note Will call the 'open' trigger.
 * @note Must be called with the mutex free.
 *
 * @param[in] pool  to modify.
 * @param[in] request The current request.
 * @param[in] now Current time.
 * @param[in] in_use  whether the new connection should be "in_use" or not
 * @param[in] unlock  whether we should unlock the mutex before returning
 * @return
 *  - New connection struct.
 *  - NULL on error.
 */
static fr_pool_connection_t *connection_spawn(fr_pool_t *pool, request_t *request, fr_time_t now, bool in_use, bool unlock)
{
  uint64_t    number;
  uint32_t    pending_window;
  TALLOC_CTX    *ctx;

  fr_pool_connection_t  *this;
  void      *conn;

  fr_assert(pool != NULL);

  /*
   *  If we have NO connections, and we've previously failed
   *  opening connections, don't open multiple connections until
   *  we successfully open at least one.
   */
  if ((pool->state.num == 0) &&
      pool->state.pending &&
      fr_time_gt(pool->state.last_failed, fr_time_wrap(0))) return NULL;

  pthread_mutex_lock(&pool->mutex);
  fr_assert(pool->state.num <= pool->max);

  /*
   *  Don't spawn too many connections at the same time.
   */
  if ((pool->state.num + pool->state.pending) >= pool->max) {
    pthread_mutex_unlock(&pool->mutex);

    ERROR("Cannot open new connection, already at max");
    return NULL;
  }

  /*
   *  If the last attempt failed, wait a bit before
   *  retrying.
   */
  if (fr_time_gt(pool->state.last_failed, fr_time_wrap(0)) &&
      fr_time_gt(fr_time_add(pool->state.last_failed, pool->retry_delay), now)) {
    bool complain = false;

    if (fr_time_delta_gteq(fr_time_sub(now, pool->state.last_throttled), fr_time_delta_from_sec(1))) {
      complain = true;

      pool->state.last_throttled = now;
    }

    pthread_mutex_unlock(&pool->mutex);

    if (!fr_rate_limit_enabled() || complain) {
      ERROR("Last connection attempt failed, waiting %pV seconds before retrying",
            fr_box_time_delta(fr_time_sub(fr_time_add(pool->state.last_failed, pool->retry_delay), now)));
    }

    return NULL;
  }

  /*
   *  We limit the rate of new connections after a failed attempt.
   */
  if (pool->state.pending > pool->pending_window) {
    pthread_mutex_unlock(&pool->mutex);

    RATE_LIMIT_GLOBAL_ROPTIONAL(RWARN, WARN,
              "Cannot open a new connection due to rate limit after failure");

    return NULL;
  }

  pool->state.pending++;
  number = pool->state.count++;

  /*
   *  Don't starve out the thread trying to reconnect
   *  the pool, by continuously opening new connections.
   */
  while (pool->state.reconnecting) pthread_cond_wait(&pool->done_reconnecting, &pool->mutex);

  /*
   *  The true value for pending_window is the smaller of
   *  free connection slots, or pool->pending_window.
   */
  pending_window = (pool->max - pool->state.num);
  if (pool->pending_window < pending_window) pending_window = pool->pending_window;
  ROPTIONAL(RDEBUG2, DEBUG2, "Opening additional connection (%" PRIu64 "), %u of %u pending slots used",
      number, pool->state.pending, pending_window);

  /*
   *  Unlock the mutex while we try to open a new
   *  connection.  If there are issues with the back-end,
   *  opening a new connection may take a LONG time.  In
   *  that case, we want the other connections to continue
   *  to be used.
   */
  pthread_mutex_unlock(&pool->mutex);

  /*
   *  Allocate a new top level ctx for the create callback
   *  to hang its memory off of.
   */
  MEM(ctx = talloc_init("connection_ctx"));

  /*
   *  This may take a long time, which prevents other
   *  threads from releasing connections.  We don't care
   *  about other threads opening new connections, as we
   *  already have no free connections.
   */
  conn = pool->create(ctx, pool->opaque, pool->connect_timeout);
  if (!conn) {
    ERROR("Opening connection failed (%" PRIu64 ")", number);

    pthread_mutex_lock(&pool->mutex);
    pool->state.last_failed = now;
    pool->pending_window = 1;
    pool->state.pending--;

    /*
     *  Must be done inside the mutex, reconnect callback
     *  may modify args.
     */
    fr_pool_trigger(pool, "fail");
    pthread_cond_broadcast(&pool->done_spawn);
    pthread_mutex_unlock(&pool->mutex);

    talloc_free(ctx);

    return NULL;
  }

  /*
   *  And lock the mutex again while we link the new
   *  connection back into the pool.
   */
  pthread_mutex_lock(&pool->mutex);

  this = talloc_zero(pool, fr_pool_connection_t);
  if (!this) {
    pool->state.last_failed = now;
    pool->state.pending--;

    pthread_cond_broadcast(&pool->done_spawn);
    pthread_mutex_unlock(&pool->mutex);

    ERROR("Memory allocation failed for new connection (%" PRIu64 ")", number);

    talloc_free(ctx);

    return NULL;
  }
  MEM(talloc_link_ctx(this, ctx) >= 0);

  this->created = now;
  this->connection = conn;
  this->in_use = in_use;

  this->number = number;
  this->last_reserved = fr_time();
  this->last_released = this->last_reserved;

  /*
   *  The connection pool is starting up.  Insert the
   *  connection into the heap.
   */
  if (!in_use) fr_heap_insert(&pool->heap, this);

  connection_link_head(pool, this);

  /*
   *  Do NOT insert the connection into the heap.  That's
   *  done when the connection is released.
   */

  pool->state.num++;

  fr_assert(pool->state.pending > 0);
  pool->state.pending--;

  /*
   *  We've successfully opened one more connection.  Allow
   *  more connections to open in parallel.
   */
  if ((pool->pending_window < pool->max) &&
      ((pool->max_pending == 0) || (pool->pending_window < pool->max_pending))) {
    pool->pending_window++;
  }

  pool->state.last_spawned = fr_time();
  pool->delay_interval = pool->cleanup_interval;
  pool->state.next_delay = pool->cleanup_interval;
  pool->state.last_failed = fr_time_wrap(0);

  /*
   *  Must be done inside the mutex, reconnect callback
   *  may modify args.
   */
  fr_pool_trigger(pool, "open");

  pthread_cond_broadcast(&pool->done_spawn);
  if (unlock) pthread_mutex_unlock(&pool->mutex);

  /* coverity[missing_unlock] */
  return this;
}

/** Close an existing connection.
 *
 * Removes the connection from the list, calls the delete callback to close
 * the connection, then frees memory allocated to the connection.
 *
 * @note Will call the 'close' trigger.
 * @note Must be called with the mutex held.
 *
 * @param[in] pool  to modify.
 * @param[in] this  Connection to delete.
 */
static void connection_close_internal(fr_pool_t *pool, fr_pool_connection_t *this)
{
  /*
   *  If it's in use, release it.
   */
  if (this->in_use) {
#ifdef PTHREAD_DEBUG
    pthread_t pthread_id = pthread_self();
    fr_assert(pthread_equal(this->pthread_id, pthread_id) != 0);
#endif

    this->in_use = false;

    fr_assert(pool->state.active != 0);
    pool->state.active--;

  } else {
    /*
     *  Connection isn't used, remove it from the heap.
     */
    fr_heap_extract(&pool->heap, this);
  }

  fr_pool_trigger(pool, "close");

  connection_unlink(pool, this);

  fr_assert(pool->state.num > 0);
  pool->state.num--;
  talloc_free(this);
}

/** Check whether a connection needs to be removed from the pool
 *
 * Will verify that the connection is within idle_timeout, max_uses, and
 * lifetime values. If it is not, the connection will be closed.
 *
 * @note Will only close connections not in use.
 * @note Must be called with the mutex held.
 *
 * @param[in] pool  to modify.
 * @param[in] request The current request.
 * @param[in] this  Connection to manage.
 * @param[in] now Current time.
 * @return
 *  - 0 if connection was closed.
 *  - 1 if connection handle was left open.
 */
static int connection_manage(fr_pool_t *pool, request_t *request, fr_pool_connection_t *this, fr_time_t now)
{
  fr_assert(pool != NULL);
  fr_assert(this != NULL);

  /*
   *  Don't terminated in-use connections
   */
  if (this->in_use) return 1;

  if (this->needs_reconnecting) {
    ROPTIONAL(RDEBUG2, DEBUG2, "Closing expired connection (%" PRIu64 "): Needs reconnecting",
        this->number);
  do_delete:
    if (pool->state.num <= pool->min) {
      ROPTIONAL(RDEBUG2, DEBUG2, "You probably need to lower \"min\"");
    }
    connection_close_internal(pool, this);
    return 0;
  }

  if ((pool->max_uses > 0) &&
      (this->num_uses >= pool->max_uses)) {
    ROPTIONAL(RDEBUG2, DEBUG2, "Closing expired connection (%" PRIu64 "): Hit max_uses limit",
        this->number);
    goto do_delete;
  }

  if (fr_time_delta_ispos(pool->lifetime) &&
      (fr_time_lt(fr_time_add(this->created, pool->lifetime), now))) {
    ROPTIONAL(RDEBUG2, DEBUG2, "Closing expired connection (%" PRIu64 "): Hit lifetime limit",
        this->number);
    goto do_delete;
  }

  if (fr_time_delta_ispos(pool->idle_timeout) &&
      (fr_time_lt(fr_time_add(this->last_released, pool->idle_timeout), now))) {
    ROPTIONAL(RINFO, INFO, "Closing connection (%" PRIu64 "): Hit idle_timeout, was idle for %pVs",
            this->number, fr_box_time_delta(fr_time_sub(now, this->last_released)));
    goto do_delete;
  }

  return 1;
}


/** Check whether any connections need to be removed from the pool
 *
 * Maintains the number of connections in the pool as per the configuration
 * parameters for the connection pool.
 *
 * @note Will only run checks the first time it's called in a given second,
 * to throttle connection spawning/closing.
 * @note Will only close connections not in use.
 * @note Must be called with the mutex held, will release mutex before returning.
 *
 * @param[in] pool  to manage.
 * @param[in] request The current request.
 * @return 1
 */
static int connection_check(fr_pool_t *pool, request_t *request)
{
  uint32_t    num, spare;
  fr_time_t   now = fr_time();
  fr_pool_connection_t  *this, *next;

  if (fr_time_delta_lt(fr_time_sub(now, pool->state.last_checked), fr_time_delta_from_sec(1))) {
    pthread_mutex_unlock(&pool->mutex);
    return 1;
  }

  /*
   *  Get "real" number of connections, and count pending
   *  connections as spare.
   */
  num = pool->state.num + pool->state.pending;
  spare = pool->state.pending + (pool->state.num - pool->state.active);

  /*
   *  The other end can close connections.  If so, we'll
   *  have fewer than "min".  When that happens, open more
   *  connections to enforce "min".
   *
   *  The code for spawning connections enforces that
   *  num + pending <= max.
   */
  if (num < pool->min) {
    ROPTIONAL(RINFO, INFO, "Need %i more connections to reach min connections (%i)", pool->min - num, pool->min);
    goto add_connection;
  }

  /*
   *  On the odd chance that we've opened too many
   *  connections, take care of that.
   */
  if (num > pool->max) {
    /*
     *  Pending connections don't get closed as "spare".
     */
    if (pool->state.pending > 0) goto manage_connections;

    /*
     *  Otherwise close one of the connections to
     *  bring us down to "max".
     */
    goto close_connection;
  }

  /*
   *  Now that we've enforced min/max connections, try to
   *  keep the "spare" connections at the correct number.
   */

  /*
   *  Nothing to do?  Go check all of the connections for
   *  timeouts, etc.
   */
  if (spare == pool->spare) goto manage_connections;

  /*
   *  Too many spare connections, delete some.
   */
  if (spare > pool->spare) {
    fr_pool_connection_t *found;

    /*
     *  Pending connections don't get closed as "spare".
     */
    if (pool->state.pending > 0) goto manage_connections;

    /*
     *  Don't close too many connections, even they
     *  are spare.
     */
    if (num <= pool->min) goto manage_connections;

    /*
     *  Too many spares, go close one.
     */

  close_connection:
    /*
     *  Don't close connections too often, in order to
     *  prevent flapping. Coverity doesn't notice that
     *  all callers have the lock, so we annotate the issue.
     */
    /* coverity[missing_lock] */
    if (fr_time_lt(now, fr_time_add(pool->state.last_spawned, pool->delay_interval))) goto manage_connections;

    /*
     *  Find a connection to close.
     */
    found = NULL;
    for (this = pool->tail; this != NULL; this = this->prev) {
      if (this->in_use) continue;

      if (!found || (fr_time_lt(this->last_reserved, found->last_reserved))) found = this;
    }

    if (!fr_cond_assert(found)) goto done;

    ROPTIONAL(RDEBUG2, DEBUG2, "Closing connection (%" PRIu64 ") as we have too many unused connections",
        found->number);
    connection_close_internal(pool, found);

    /*
     *  Decrease the delay for the next time we clean
     *  up.
     */
    pool->state.next_delay = fr_time_delta_wrap(fr_time_delta_unwrap(pool->state.next_delay) >> 1);
    if (!fr_time_delta_ispos(pool->state.next_delay)) pool->state.next_delay = fr_time_delta_wrap(1);
    pool->delay_interval = fr_time_delta_add(pool->delay_interval, pool->state.next_delay);

    goto manage_connections;
  }

  /*
   *  Too few connections, open some more.
   */
  if (spare < pool->spare) {
    /*
     *  Don't open too many pending connections.
     *  Again, coverity doesn't realize all callers have the lock,
     *  so we must annotate here as well.
     */
    /* coverity[missing_lock] */
    if (pool->state.pending >= pool->pending_window) goto manage_connections;

    /*
     *  Don't open too many connections, even if we
     *  need more spares.
     */
    if (num >= pool->max) goto manage_connections;

    /*
     *  Too few spares, go add one.
     */
    ROPTIONAL(RINFO, INFO, "Need %i more connections to reach %i spares", pool->spare - spare, pool->spare);

  add_connection:
    /*
     *  Only try to open spares if we're not already attempting to open
     *  a connection. Avoids spurious log messages.
     */
    pthread_mutex_unlock(&pool->mutex);
    (void) connection_spawn(pool, request, now, false, true);
    pthread_mutex_lock(&pool->mutex);
    goto manage_connections;
  }

  /*
   *  Pass over all of the connections in the pool, limiting
   *  lifetime, idle time, max requests, etc.
   */
manage_connections:
  for (this = pool->head; this != NULL; this = next) {
    next = this->next;
    connection_manage(pool, request, this, now);
  }

  pool->state.last_checked = now;

done:
  pthread_mutex_unlock(&pool->mutex);

  return 1;
}

/** Get a connection from the connection pool
 *
 * @note Must be called with the mutex free.
 *
 * @param[in] pool  to reserve the connection from.
 * @param[in] request The current request.
 * @param[in] spawn whether to spawn a new connection
 * @return
 *  - A pointer to the connection handle.
 *  - NULL on error.
 */
static void *connection_get_internal(fr_pool_t *pool, request_t *request, bool spawn)
{
  fr_time_t now;
  fr_pool_connection_t *this;

  if (!pool) return NULL;

  pthread_mutex_lock(&pool->mutex);

  now = fr_time();

  /*
   *  Grab the link with the lowest latency, and check it
   *  for limits.  If "connection manage" says the link is
   *  no longer usable, go grab another one.
   */
  do {
    this = fr_heap_peek(pool->heap);
    if (!this) break;
  } while (!connection_manage(pool, request, this, now));

  /*
   *  We have a working connection.  Extract it from the
   *  heap and use it.
   */
  if (this) {
    fr_heap_extract(&pool->heap, this);
    goto do_return;
  }

  if (pool->state.num == pool->max) {
    bool complain = false;

    /*
     *  Rate-limit complaints.
     */
    if (fr_time_delta_gt(fr_time_sub(now, pool->state.last_at_max), fr_time_delta_from_sec(1))) {
      complain = true;
      pool->state.last_at_max = now;
    }

    if (!fr_rate_limit_enabled() || complain) {
      ERROR("No connections available and at max connection limit");

      /*
       *  Must be done inside the mutex, reconnect callback
       *  may modify args.
       */
      fr_pool_trigger(pool, "none");
    }
    pthread_mutex_unlock(&pool->mutex);

    return NULL;
  }

  pthread_mutex_unlock(&pool->mutex);

  if (!spawn) return NULL;

  ROPTIONAL(RDEBUG2, DEBUG2, "%i of %u connections in use.  You may need to increase \"spare\"",
         pool->state.active, pool->state.num);

  /*
   *  Returns unlocked on failure, or locked on success
   */
  this = connection_spawn(pool, request, now, true, false);
  if (!this) return NULL;

do_return:
  pool->state.active++;
  this->num_uses++;
  this->last_reserved = fr_time();
  this->in_use = true;

#ifdef PTHREAD_DEBUG
  this->pthread_id = pthread_self();
#endif
  pthread_mutex_unlock(&pool->mutex);

  ROPTIONAL(RDEBUG2, DEBUG2, "Reserved connection (%" PRIu64 ")", this->number);

  return this->connection;
}

/** Enable triggers for a connection pool
 *
 * @param[in] pool    to enable triggers for.
 * @param[in] trigger_prefix  prefix to prepend to all trigger names.  Usually a path
 *        to the module's trigger configuration e.g.
 *            @verbatim modules.<name>.pool @endverbatim
 *        @verbatim <trigger name> @endverbatim is appended to form
 *        the complete path.
 * @param[in] trigger_args  to make available in any triggers executed by the connection pool.
 *        These will usually be fr_pair_t (s) describing the host
 *        associated with the pool.
 *        Trigger args will be copied, input trigger_args should be freed
 *        if necessary.
 */
void fr_pool_enable_triggers(fr_pool_t *pool, char const *trigger_prefix, fr_pair_list_t *trigger_args)
{
  pool->triggers_enabled = true;

  talloc_const_free(pool->trigger_prefix);
  MEM(pool->trigger_prefix = trigger_prefix ? talloc_strdup(pool, trigger_prefix) : "");

  fr_pair_list_free(&pool->trigger_args);

  if (!trigger_args) return;

  MEM(fr_pair_list_copy(pool, &pool->trigger_args, trigger_args) >= 0);
}

/** Create a new connection pool
 *
 * Allocates structures used by the connection pool, initialises the various
 * configuration options and counters, and sets the callback functions.
 *
 * Will also spawn the number of connections specified by the 'start' configuration
 * option.
 *
 * @note Will call the 'start' trigger.
 *
 * @param[in] ctx   Context to link pool's destruction to.
 * @param[in] cs    pool section.
 * @param[in] opaque data pointer to pass to callbacks.
 * @param[in] c     Callback to create new connections.
 * @param[in] a     Callback to check the status of connections.
 * @param[in] log_prefix  prefix to prepend to all log messages.
 * @return
 *  - New connection pool.
 *  - NULL on error.
 */
fr_pool_t *fr_pool_init(TALLOC_CTX *ctx,
      CONF_SECTION const *cs,
      void *opaque,
      fr_pool_connection_create_t c, fr_pool_connection_alive_t a,
      char const *log_prefix)
{
  fr_pool_t   *pool = NULL;

  if (!cs || !opaque || !c) return NULL;

  /*
   *  Pool is allocated in the NULL context as
   *  threads are likely to allocate memory
   *  beneath the pool.
   */
  MEM(pool = talloc_zero(NULL, fr_pool_t));
  fr_pair_list_init(&pool->trigger_args);

  /*
   *  Ensure the pool is freed at the same time
   *  as its parent.
   */
  if (ctx && (talloc_link_ctx(ctx, pool) < 0)) {
    PERROR("%s: Failed linking pool ctx", __FUNCTION__);
    talloc_free(pool);

    return NULL;
  }

  pool->cs = cs;
  pool->opaque = opaque;
  pool->create = c;
  pool->alive = a;

  pool->head = pool->tail = NULL;

  /*
   *  We keep a heap of connections, sorted by the last time
   *  we STARTED using them.  Newly opened connections
   *  aren't in the heap.  They're only inserted in the list
   *  once they're released.
   *
   *  We do "most recently started" instead of "most
   *  recently used", because MRU is done as most recently
   *  *released*.  We want to order connections by
   *  responsiveness, and MRU prioritizes high latency
   *  connections.
   *
   *  We want most recently *started*, which gives
   *  preference to low latency links, and pushes high
   *  latency links down in the priority heap.
   *
   *  https://code.facebook.com/posts/1499322996995183/solving-the-mystery-of-link-imbalance-a-metastable-failure-state-at-scale/
   */
  if (!pool->spread) {
    pool->heap = fr_heap_talloc_alloc(pool, last_reserved_cmp, fr_pool_connection_t, heap_id, 0);
  /*
   *  For some types of connections we need to used a different
   *  algorithm, because load balancing benefits are secondary
   *  to maintaining a cache of open connections.
   *
   *  With libcurl's multihandle, connections can only be reused
   *  if all handles that make up the multihandle are done processing
   *  their requests.
   *
   *  We can't tell when that's happened using libcurl, and even
   *  if we could, blocking until all servers had responded
   *  would have huge cost.
   *
   *  The solution is to order the heap so that the connection that
   *  was released longest ago is at the top.
   *
   *  That way we maximise time between connection use.
   */
  } else {
    pool->heap = fr_heap_talloc_alloc(pool, last_released_cmp, fr_pool_connection_t, heap_id, 0);
  }
  if (!pool->heap) {
    ERROR("%s: Failed creating connection heap", __FUNCTION__);
  error:
    fr_pool_free(pool);
    return NULL;
  }

  pool->log_prefix = log_prefix ? talloc_strdup(pool, log_prefix) : "core";
  pthread_mutex_init(&pool->mutex, NULL);
  pthread_cond_init(&pool->done_spawn, NULL);
  pthread_cond_init(&pool->done_reconnecting, NULL);

  DEBUG2("Initialising connection pool");

  if (cf_section_rules_push(UNCONST(CONF_SECTION *, cs), pool_config) < 0) goto error;
  if (cf_section_parse(pool, pool, UNCONST(CONF_SECTION *, cs)) < 0) {
    PERROR("Configuration parsing failed");
    goto error;
  }

  /*
   *  Some simple limits
   */
  if (pool->max == 0) {
    cf_log_err(cs, "Cannot set 'max' to zero");
    goto error;
  }

  /*
   *  Coverity notices that other uses of max_pending are protected with a mutex,
   *  and thus thinks it should be locked/unlocked here...but coverity does not
   *  consider that until this function returns a pointer to a pool, nobody can
   *  use the pool, so there's no point to doing so.
   */
  /* coverity[missing_lock] */
  pool->pending_window = (pool->max_pending > 0) ? pool->max_pending : pool->max;

  if (pool->min > pool->max) {
    cf_log_err(cs, "Cannot set 'min' to more than 'max'");
    goto error;
  }

  FR_INTEGER_BOUND_CHECK("max", pool->max, <=, 1024);
  FR_INTEGER_BOUND_CHECK("start", pool->start, <=, pool->max);
  FR_INTEGER_BOUND_CHECK("spare", pool->spare, <=, (pool->max - pool->min));

  if (fr_time_delta_ispos(pool->lifetime)) {
    FR_TIME_DELTA_COND_CHECK("idle_timeout", pool->idle_timeout,
           fr_time_delta_lteq(pool->idle_timeout, pool->lifetime), fr_time_delta_wrap(0));
  }

  if (fr_time_delta_ispos(pool->idle_timeout)) {
    FR_TIME_DELTA_BOUND_CHECK("cleanup_interval", pool->cleanup_interval, <=, pool->idle_timeout);
  }

  /*
   *  Some libraries treat 0.0 as infinite timeout, others treat it
   *  as instantaneous timeout.  Solve the inconsistency by making
   *  the smallest allowable timeout 100ms.
   */
  FR_TIME_DELTA_BOUND_CHECK("connect_timeout", pool->connect_timeout, >=, fr_time_delta_from_msec(100));

  /*
   *  Don't open any connections.  Instead, force the limits
   *  to only 1 connection.
   *
   */
  if (check_config) pool->start = pool->min = pool->max = 1;

  return pool;
}

int fr_pool_start(fr_pool_t *pool)
{
  uint32_t    i;
  fr_pool_connection_t  *this;

  /*
   *  Don't spawn any connections
   */
  if (check_config) return 0;

  /*
   *  Create all of the connections, unless the admin says
   *  not to.
   */
  for (i = 0; i < pool->start; i++) {
    /*
     *  Call time() once for each spawn attempt as there
     *  could be a significant delay.
     */
    this = connection_spawn(pool, NULL, fr_time(), false, true);
    if (!this) {
      ERROR("Failed spawning initial connections");
      return -1;
    }
  }

  fr_pool_trigger(pool, "start");

  return 0;
}

/** Allocate a new pool using an existing one as a template
 *
 * @param[in] ctx to allocate new pool in.
 * @param[in] pool  to copy.
 * @param[in] opaque  data to pass to connection function.
 * @return
 *  - New connection pool.
 *  - NULL on error.
 */
fr_pool_t *fr_pool_copy(TALLOC_CTX *ctx, fr_pool_t *pool, void *opaque)
{
  fr_pool_t *copy;

  copy = fr_pool_init(ctx, pool->cs, opaque, pool->create, pool->alive, pool->log_prefix);
  if (!copy) return NULL;

  if (pool->trigger_prefix) fr_pool_enable_triggers(copy, pool->trigger_prefix, &pool->trigger_args);

  return copy;
}

/** Get the number of connections currently in the pool
 *
 * @param[in] pool to count connections for.
 * @return the number of connections in the pool
 */
fr_pool_state_t const *fr_pool_state(fr_pool_t *pool)
{
  return &pool->state;
}

/** Connection pool get timeout
 *
 * @param[in] pool to get connection timeout for.
 * @return the connection timeout configured for the pool.
 */
fr_time_delta_t fr_pool_timeout(fr_pool_t *pool)
{
  return pool->connect_timeout;
}

/** Connection pool get start
 *
 * @param[in] pool to get connection start for.
 * @return the connection start value configured for the pool.
 */
int fr_pool_start_num(fr_pool_t *pool)
{
  return pool->start;
}

/** Return the opaque data associated with a connection pool
 *
 * @param pool to return data for.
 * @return opaque data associated with pool.
 */
void const *fr_pool_opaque(fr_pool_t *pool)
{
  return pool->opaque;
}

/** Increment pool reference by one.
 *
 * @param[in] pool to increment reference counter for.
 */
void fr_pool_ref(fr_pool_t *pool)
{
  pool->ref++;
}

/** Set a reconnection callback for the connection pool
 *
 * This can be called at any time during the pool's lifecycle.
 *
 * @param[in] pool to set reconnect callback for.
 * @param reconnect callback to call when reconnecting pool's connections.
 */
void fr_pool_reconnect_func(fr_pool_t *pool, fr_pool_reconnect_t reconnect)
{
  pool->reconnect = reconnect;
}

/** Mark connections for reconnection, and spawn at least 'start' connections
 *
 * @note This call may block whilst waiting for pending connection attempts to complete.
 *
 * This intended to be called on a connection pool that's in use, to have it reflect
 * a configuration change, or because the administrator knows that all connections
 * in the pool are inviable and need to be reconnected.
 *
 * @param[in] pool  to reconnect.
 * @param[in] request The current request.
 * @return
 *  -  0 On success.
 *  - -1 If we couldn't create start connections, this may be ignored
 *       depending on the context in which this function is being called.
 */
int fr_pool_reconnect(fr_pool_t *pool, request_t *request)
{
  uint32_t    i;
  fr_pool_connection_t  *this;
  fr_time_t   now;

  pthread_mutex_lock(&pool->mutex);

  /*
   *  Pause new spawn attempts (we release the mutex
   *  during our cond wait).
   */
  pool->state.reconnecting = true;

  /*
   *  When the loop exits, we'll hold the lock for the pool,
   *  and we're guaranteed the connection create callback
   *  will not be using the opaque data.
   */
  while (pool->state.pending) pthread_cond_wait(&pool->done_spawn, &pool->mutex);

  /*
   *  We want to ensure at least 'start' connections
   *  have been reconnected. We can't call reconnect
   *  because, we might get the same connection each
   *  time we reserve one, so we close 'start'
   *  connections, and then attempt to spawn them again.
   */
  for (i = 0; i < pool->start; i++) {
    this = fr_heap_peek(pool->heap);
    if (!this) break; /* There wasn't 'start' connections available */

    connection_close_internal(pool, this);
  }

  /*
   *  Mark all remaining connections in the pool as
   *  requiring reconnection.
   */
  for (this = pool->head; this; this = this->next) this->needs_reconnecting = true;

  /*
   *  Call the reconnect callback (if one's set)
   *  This may modify the opaque data associated
   *  with the pool.
   */
  if (pool->reconnect) pool->reconnect(pool, pool->opaque);

  /*
   *  Must be done inside the mutex, reconnect callback
   *  may modify args.
   */
  fr_pool_trigger(pool, "reconnect");

  /*
   *  Allow new spawn attempts, and wakeup any threads
   *  waiting to spawn new connections.
   */
  pool->state.reconnecting = false;
  pthread_cond_broadcast(&pool->done_reconnecting);
  pthread_mutex_unlock(&pool->mutex);

  now = fr_time();

  /*
   *  Now attempt to spawn 'start' connections.
   */
  for (i = 0; i < pool->start; i++) {
    this = connection_spawn(pool, request, now, false, true);
    if (!this) return -1;
  }

  return 0;
}

/** Delete a connection pool
 *
 * Closes, unlinks and frees all connections in the connection pool, then frees
 * all memory used by the connection pool.
 *
 * @note Will call the 'stop' trigger.
 * @note Must be called with the mutex free.
 *
 * @param[in,out] pool to delete.
 */
void fr_pool_free(fr_pool_t *pool)
{
  fr_pool_connection_t *this;

  if (!pool) return;

  /*
   *  More modules hold a reference to this pool, don't free
   *  it yet.
   */
  if (pool->ref > 0) {
    pool->ref--;
    return;
  }

  DEBUG2("Removing connection pool");

  pthread_mutex_lock(&pool->mutex);

  /*
   *  Don't loop over the list.  Just keep removing the head
   *  until they're all gone.
   */
  while ((this = pool->head) != NULL) {
    INFO("Closing connection (%" PRIu64 ")", this->number);

    connection_close_internal(pool, this);
  }

  fr_pool_trigger(pool, "stop");

  fr_assert(pool->head == NULL);
  fr_assert(pool->tail == NULL);
  fr_assert(pool->state.num == 0);

  pthread_mutex_unlock(&pool->mutex);
  pthread_mutex_destroy(&pool->mutex);
  pthread_cond_destroy(&pool->done_spawn);
  pthread_cond_destroy(&pool->done_reconnecting);

  talloc_free(pool);
}

/** Reserve a connection in the connection pool
 *
 * Will attempt to find an unused connection in the connection pool, if one is
 * found, will mark it as in use, and increment the number of active connections
 * and return the connection handle.
 *
 * If no free connections are found will attempt to spawn a new one, conditional
 * on a connection spawning not already being in progress, and not being at the
 * 'max' connection limit.
 *
 * @note fr_pool_connection_release must be called once the caller has finished
 * using the connection.
 *
 * @see fr_pool_connection_release
 * @param[in] pool  to reserve the connection from.
 * @param[in] request The current request.
 * @return
 *  - A pointer to the connection handle.
 *  - NULL on error.
 */
void *fr_pool_connection_get(fr_pool_t *pool, request_t *request)
{
  return connection_get_internal(pool, request, true);
}

/** Release a connection
 *
 * Will mark a connection as unused and decrement the number of active
 * connections.
 *
 * @see fr_pool_connection_get
 * @param[in] pool  to release the connection in.
 * @param[in] request The current request.
 * @param[in] conn  to release.
 */
void fr_pool_connection_release(fr_pool_t *pool, request_t *request, void *conn)
{
  fr_pool_connection_t  *this;
  fr_time_delta_t   held;
  bool      trigger_min = false, trigger_max = false;

  this = connection_find(pool, conn);
  if (!this) return;

  this->in_use = false;

  /*
   *  Record when the connection was last released
   */
  this->last_released = fr_time();
  pool->state.last_released = this->last_released;

  /*
   *  This is done inside the mutex to ensure
   *  updates are atomic.
   */
  held = fr_time_sub(this->last_released, this->last_reserved);

  /*
   *  Check we've not exceeded out trigger limits
   *
   *      These should only fire once per second.
   */
  if (fr_time_delta_ispos(pool->held_trigger_min) &&
      (fr_time_delta_lt(held, pool->held_trigger_min)) &&
      (fr_time_delta_gteq(fr_time_sub(this->last_released, pool->state.last_held_min), fr_time_delta_from_sec(1)))) {
        trigger_min = true;
        pool->state.last_held_min = this->last_released;
  }

  if (fr_time_delta_ispos(pool->held_trigger_max) &&
      (fr_time_delta_gt(held, pool->held_trigger_max)) &&
      (fr_time_delta_gteq(fr_time_sub(this->last_released, pool->state.last_held_max), fr_time_delta_from_sec(1)))) {
        trigger_max = true;
        pool->state.last_held_max = this->last_released;
  }

  /*
   *  Insert the connection in the heap.
   *
   *  This will either be based on when we *started* using it
   *  (allowing fast links to be re-used, and slow links to be
   *  gradually expired), or when we released it (allowing
   *  the maximum amount of time between connection use).
   */
  fr_heap_insert(&pool->heap, this);

  fr_assert(pool->state.active != 0);
  pool->state.active--;

  ROPTIONAL(RDEBUG2, DEBUG2, "Released connection (%" PRIu64 ")", this->number);

  /*
   *  We mirror the "spawn on get" functionality by having
   *  "delete on release".  If there are too many spare
   *  connections, go manage the pool && clean some up.
   */
  connection_check(pool, request);

  if (trigger_min) fr_pool_trigger(pool, "min");
  if (trigger_max) fr_pool_trigger(pool, "max");
}

/** Reconnect a suspected inviable connection
 *
 * This should be called by the module if it suspects that a connection is
 * not viable (e.g. the server has closed it).
 *
 * When implementing a module that uses the connection pool API, it is advisable
 * to pass a pointer to the pointer to the handle (void **conn)
 * to all functions which may call reconnect. This is so that if a new handle
 * is created and returned, the handle pointer can be updated up the callstack,
 * and a function higher up the stack doesn't attempt to use a now invalid
 * connection handle.
 *
 * @note Will free any talloced memory hung off the context of the connection,
 *  being reconnected.
 *
 * @warning After calling reconnect the caller *MUST NOT* attempt to use
 *  the old handle in any other operations, as its memory will have been
 *  freed.
 *
 * @see fr_pool_connection_get
 * @param[in] pool  to reconnect the connection in.
 * @param[in] request The current request.
 * @param[in] conn  to reconnect.
 * @return new connection handle if successful else NULL.
 */
void *fr_pool_connection_reconnect(fr_pool_t *pool, request_t *request, void *conn)
{
  fr_pool_connection_t  *this;

  if (!pool || !conn) return NULL;

  /*
   *  If connection_find is successful the pool is now locked
   */
  this = connection_find(pool, conn);
  if (!this) return NULL;

  ROPTIONAL(RINFO, INFO, "Deleting inviable connection (%" PRIu64 ")", this->number);

  connection_close_internal(pool, this);
  connection_check(pool, request);      /* Whilst we still have the lock (will release the lock) */

  /*
   *  Return an existing connection or spawn a new one.
   */
  return connection_get_internal(pool, request, true);
}

/** Delete a connection from the connection pool.
 *
 * Resolves the connection handle to a connection, then (if found)
 * closes, unlinks and frees that connection.
 *
 * @note Must be called with the mutex free.
 *
 * @param[in] pool  Connection pool to modify.
 * @param[in] request The current request.
 * @param[in] conn  to delete.
 * @return
 *  - 0 If the connection could not be found.
 *  - 1 if the connection was deleted.
 */
int fr_pool_connection_close(fr_pool_t *pool, request_t *request, void *conn)
{
  fr_pool_connection_t *this;

  this = connection_find(pool, conn);
  if (!this) return 0;

  /*
   *  Record the last time a connection was closed
   */
  pool->state.last_closed = fr_time();

  ROPTIONAL(RINFO, INFO, "Deleting connection (%" PRIu64 ")", this->number);

  connection_close_internal(pool, this);
  connection_check(pool, request);
  return 1;
}

Coverage Report

Created: 2026-03-31 06:21