src/lib/object-pool.h

   1 /*
   2  * SPDX-License-Identifier: MIT
   3  *
   4  * Copyright (c) 2018 Philippe Proulx <pproulx@efficios.com>
   5  */
   6
   7 #ifndef BABELTRACE_OBJECT_POOL_INTERNAL_H
   8 #define BABELTRACE_OBJECT_POOL_INTERNAL_H
   9
  10 /*
  11  * This is a generic object pool to avoid memory allocation/deallocation
  12  * for objects of which the lifespan is typically short, but which are
  13  * created a lot.
  14  *
  15  * The object pool, thanks to two user functions, knows how to allocate
  16  * a brand new object in memory when the pool is empty and how to
  17  * destroy an object when we destroy the pool.
  18  *
  19  * The object pool's user is responsible for:
  20  *
  21  * * Setting whatever references the object needs to keep and reset some
  22  *   properties _after_ calling bt_object_pool_create_object(). This is
  23  *   typically done in the bt_*_create() function which calls
  24  *   bt_object_pool_create_object() (which could call the user-provided
  25  *   allocation function if the pool is empty) and then sets the
  26  *   appropriate properties on the possibly recycled object.
  27  *
  28  * * Releasing whatever references the object keeps _before_ calling
  29  *   bt_object_pool_recycle_object(). This is typically done in a custom
  30  *   bt_*_recycle() function which does the necessary before calling
  31  *   bt_object_pool_recycle_object() with an object ready to be reused
  32  *   at any time.
  33  */
  34
  35 #include <glib.h>
  36 #include "lib/object.h"
  37
  38 /* Protection: this file uses BT_LIB_LOG*() macros directly */
  39 #ifndef BT_LIB_LOG_SUPPORTED
  40 # error Please include "lib/logging.h" before including this file.
  41 #endif
  42
  43 typedef void *(*bt_object_pool_new_object_func)(void *data);
  44 typedef void (*bt_object_pool_destroy_object_func)(void *obj, void *data);
  45
  46 struct bt_object_pool {
  47         /*
  48          * Container of recycled objects, owned by this. The array's size
  49          * is the pool's capacity.
  50          */
  51         GPtrArray *objects;
  52
  53         /*
  54          * Pool's size, that is, number of elements in the array above,
  55          * starting at index 0, which exist as recycled objects.
  56          */
  57         size_t size;
  58
  59         /* User functions */
  60         struct {
  61                 /* Allocate a new object in memory */
  62                 bt_object_pool_new_object_func new_object;
  63
  64                 /* Free direct and indirect memory occupied by object */
  65                 bt_object_pool_destroy_object_func destroy_object;
  66         } funcs;
  67
  68         /* User data passed to user functions */
  69         void *data;
  70 };
  71
  72 /*
  73  * Initializes an object pool which is already allocated.
  74  */
  75 BT_HIDDEN
  76 int bt_object_pool_initialize(struct bt_object_pool *pool,
  77                 bt_object_pool_new_object_func new_object_func,
  78                 bt_object_pool_destroy_object_func destroy_object_func,
  79                 void *data);
  80
  81 /*
  82  * Finalizes an object pool without deallocating it.
  83  */
  84 BT_HIDDEN
  85 void bt_object_pool_finalize(struct bt_object_pool *pool);
  86
  87 /*
  88  * Creates an object from an object pool. If the pool is empty, this
  89  * function calls the "new" user function to allocate a new object
  90  * before returning it. Otherwise this function returns a recycled
  91  * object, removing it from the pool.
  92  *
  93  * The returned object is owned by the caller.
  94  */
  95 static inline
  96 void *bt_object_pool_create_object(struct bt_object_pool *pool)
  97 {
  98         struct bt_object *obj;
  99
 100         BT_ASSERT_DBG(pool);
 101         BT_LOGT("Creating object from pool: pool-addr=%p, pool-size=%zu, pool-cap=%u",
 102                 pool, pool->size, pool->objects->len);
 103
 104         if (pool->size > 0) {
 105                 /* Pick one from the pool */
 106                 pool->size--;
 107                 obj = pool->objects->pdata[pool->size];
 108                 pool->objects->pdata[pool->size] = NULL;
 109                 goto end;
 110         }
 111
 112         /* Pool is empty: create a brand new object */
 113         BT_LOGD("Pool is empty: allocating new object: pool-addr=%p",
 114                 pool);
 115         obj = pool->funcs.new_object(pool->data);
 116
 117 end:
 118         BT_LOGT("Created one object from pool: pool-addr=%p, obj-addr=%p",
 119                 pool, obj);
 120         return obj;
 121 }
 122
 123 /*
 124  * Recycles an object, that is, puts it back into the pool.
 125  *
 126  * The pool becomes the sole owner of the object to recycle.
 127  */
 128 static inline
 129 void bt_object_pool_recycle_object(struct bt_object_pool *pool, void *obj)
 130 {
 131         struct bt_object *bt_obj = obj;
 132
 133         BT_ASSERT_DBG(pool);
 134         BT_ASSERT_DBG(obj);
 135         BT_LOGT("Recycling object: pool-addr=%p, pool-size=%zu, pool-cap=%u, obj-addr=%p",
 136                 pool, pool->size, pool->objects->len, obj);
 137
 138         if (pool->size == pool->objects->len) {
 139                 /* Backing array is full: make place for recycled object */
 140                 BT_LOGD("Object pool is full: increasing object pool capacity: "
 141                         "pool-addr=%p, old-pool-cap=%u, new-pool-cap=%u",
 142                         pool, pool->objects->len, pool->objects->len + 1);
 143                 g_ptr_array_set_size(pool->objects, pool->size + 1);
 144         }
 145
 146         /* Reset reference count to 1 since it could be 0 now */
 147         bt_obj->ref_count = 1;
 148
 149         /* Back to the pool */
 150         pool->objects->pdata[pool->size] = obj;
 151         pool->size++;
 152         BT_LOGT("Recycled object: pool-addr=%p, pool-size=%zu, pool-cap=%u, obj-addr=%p",
 153                 pool, pool->size, pool->objects->len, obj);
 154 }
 155
 156 #endif /* BABELTRACE_OBJECT_POOL_INTERNAL_H */