tor-browser

refstruct.h (12171B)

---

/*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/

#ifndef AVUTIL_REFSTRUCT_H
#define AVUTIL_REFSTRUCT_H

#include <stddef.h>

/**
* RefStruct is an API for creating reference-counted objects
* with minimal overhead. The API is designed for objects,
* not buffers like the AVBuffer API. The main differences
* to the AVBuffer API are as follows:
*
* - It uses void* instead of uint8_t* as its base type due to
*   its focus on objects.
* - There are no equivalents of AVBuffer and AVBufferRef.
*   E.g. there is no way to get the usable size of the object:
*   The user is supposed to know what is at the other end of
*   the pointer. It also avoids one level of indirection.
* - Custom allocators are not supported. This allows to simplify
*   the implementation and reduce the amount of allocations.
* - It also has the advantage that the user's free callback need
*   only free the resources owned by the object, but not the
*   object itself.
* - Because referencing (and replacing) an object managed by the
*   RefStruct API does not involve allocations, they can not fail
*   and therefore need not be checked.
*
* @note Referencing and unreferencing the buffers is thread-safe and thus
* may be done from multiple threads simultaneously without any need for
* additional locking.
*/

/**
* This union is used for all opaque parameters in this API to spare the user
* to cast const away in case the opaque to use is const-qualified.
*
* The functions provided by this API with an AVRefStructOpaque come in pairs
* named foo_c and foo. The foo function accepts void* as opaque and is just
* a wrapper around the foo_c function; "_c" means "(potentially) const".
*/
typedef union {
   void *nc;
   const void *c;
} AVRefStructOpaque;

/**
* If this flag is set in av_refstruct_alloc_ext_c(), the object will not
* be initially zeroed.
*/
#define AV_REFSTRUCT_FLAG_NO_ZEROING (1 << 0)

/**
* Allocate a refcounted object of usable size `size` managed via
* the RefStruct API.
*
* By default (in the absence of flags to the contrary),
* the returned object is initially zeroed.
*
* @param size    Desired usable size of the returned object.
* @param flags   A bitwise combination of av_refstruct_FLAG_* flags.
* @param opaque  A pointer that will be passed to the free_cb callback.
* @param free_cb A callback for freeing this object's content
*                when its reference count reaches zero;
*                it must not free the object itself.
* @return A pointer to an object of the desired size or NULL on failure.
*/
void *av_refstruct_alloc_ext_c(size_t size, unsigned flags, AVRefStructOpaque opaque,
                              void (*free_cb)(AVRefStructOpaque opaque, void *obj));

/**
* A wrapper around av_refstruct_alloc_ext_c() for the common case
* of a non-const qualified opaque.
*
* @see av_refstruct_alloc_ext_c()
*/
static inline
void *av_refstruct_alloc_ext(size_t size, unsigned flags, void *opaque,
                            void (*free_cb)(AVRefStructOpaque opaque, void *obj))
{
   return av_refstruct_alloc_ext_c(size, flags, (AVRefStructOpaque){.nc = opaque},
                                   free_cb);
}

/**
* Equivalent to av_refstruct_alloc_ext(size, 0, NULL, NULL)
*/
static inline
void *av_refstruct_allocz(size_t size)
{
   return av_refstruct_alloc_ext(size, 0, NULL, NULL);
}

/**
* Decrement the reference count of the underlying object and automatically
* free the object if there are no more references to it.
*
* `*objp == NULL` is legal and a no-op.
*
* @param objp Pointer to a pointer that is either NULL or points to an object
*             managed via this API. `*objp` is set to NULL on return.
*/
void av_refstruct_unref(void *objp);

/**
* Create a new reference to an object managed via this API,
* i.e. increment the reference count of the underlying object
* and return obj.
* @return a pointer equal to obj.
*/
void *av_refstruct_ref(void *obj);

/**
* Analog of av_refstruct_ref(), but for constant objects.
* @see av_refstruct_ref()
*/
const void *av_refstruct_ref_c(const void *obj);

/**
* Ensure `*dstp` refers to the same object as src.
*
* If `*dstp` is already equal to src, do nothing. Otherwise unreference `*dstp`
* and replace it with a new reference to src in case `src != NULL` (this
* involves incrementing the reference count of src's underlying object) or
* with NULL otherwise.
*
* @param dstp Pointer to a pointer that is either NULL or points to an object
*             managed via this API.
* @param src  A pointer to an object managed via this API or NULL.
*/
void av_refstruct_replace(void *dstp, const void *src);

/**
* Check whether the reference count of an object managed
* via this API is 1.
*
* @param obj A pointer to an object managed via this API.
* @return 1 if the reference count of obj is 1; 0 otherwise.
*/
int av_refstruct_exclusive(const void *obj);

/**
* AVRefStructPool is an API for a thread-safe pool of objects managed
* via the RefStruct API.
*
* Frequently allocating and freeing large or complicated objects may be slow
* and wasteful. This API is meant to solve this in cases when the caller
* needs a set of interchangable objects.
*
* At the beginning, the user must call allocate the pool via
* av_refstruct_pool_alloc() or its analogue av_refstruct_pool_alloc_ext().
* Then whenever an object is needed, call av_refstruct_pool_get() to
* get a new or reused object from the pool. This new object works in all
* aspects the same way as the ones created by av_refstruct_alloc_ext().
* However, when the last reference to this object is unreferenced, it is
* (optionally) reset and returned to the pool instead of being freed and
* will be reused for subsequent av_refstruct_pool_get() calls.
*
* When the caller is done with the pool and no longer needs to create any new
* objects, av_refstruct_pool_uninit() must be called to mark the pool as
* freeable. Then entries returned to the pool will then be freed.
* Once all the entries are freed, the pool will automatically be freed.
*
* Allocating and releasing objects with this API is thread-safe as long as
* the user-supplied callbacks (if provided) are thread-safe.
*/

/**
* The buffer pool. This structure is opaque and not meant to be accessed
* directly. It is allocated with the allocators below and freed with
* av_refstruct_pool_uninit().
*/
typedef struct AVRefStructPool AVRefStructPool;

/**
* If this flag is not set, every object in the pool will be zeroed before
* the init callback is called or before it is turned over to the user
* for the first time if no init callback has been provided.
*/
#define AV_REFSTRUCT_POOL_FLAG_NO_ZEROING         AV_REFSTRUCT_FLAG_NO_ZEROING
/**
* If this flag is set and both init_cb and reset_cb callbacks are provided,
* then reset_cb will be called if init_cb fails.
* The object passed to reset_cb will be in the state left by init_cb.
*/
#define AV_REFSTRUCT_POOL_FLAG_RESET_ON_INIT_ERROR                   (1 << 16)
/**
* If this flag is set and both init_cb and free_entry_cb callbacks are
* provided, then free_cb will be called if init_cb fails.
*
* It will be called after reset_cb in case reset_cb and the
* av_refstruct_POOL_FLAG_RESET_ON_INIT_ERROR flag are also set.
*
* The object passed to free_cb will be in the state left by
* the callbacks applied earlier (init_cb potentially followed by reset_cb).
*/
#define AV_REFSTRUCT_POOL_FLAG_FREE_ON_INIT_ERROR                    (1 << 17)
/**
* If this flag is set, the entries will be zeroed before
* being returned to the user (after the init or reset callbacks
* have been called (if provided)). Furthermore, to avoid zeroing twice
* it also makes the pool behave as if the av_refstruct_POOL_FLAG_NO_ZEROING
* flag had been provided.
*/
#define AV_REFSTRUCT_POOL_FLAG_ZERO_EVERY_TIME                       (1 << 18)

/**
* Equivalent to av_refstruct_pool_alloc(size, flags, NULL, NULL, NULL, NULL, NULL)
*/
AVRefStructPool *av_refstruct_pool_alloc(size_t size, unsigned flags);

/**
* Allocate an AVRefStructPool, potentially using complex callbacks.
*
* @param size size of the entries of the pool
* @param flags a bitwise combination of av_refstruct_POOL_FLAG_* flags
* @param opaque A pointer that will be passed to the callbacks below.
* @param init  A callback that will be called directly after a new entry
*              has been allocated. obj has already been zeroed unless
*              the av_refstruct_POOL_FLAG_NO_ZEROING flag is in use.
* @param reset A callback that will be called after an entry has been
*              returned to the pool and before it is reused.
* @param free_entry A callback that will be called when an entry is freed
*                   after the pool has been marked as to be uninitialized.
* @param free       A callback that will be called when the pool itself is
*                   freed (after the last entry has been returned and freed).
*/
AVRefStructPool *av_refstruct_pool_alloc_ext_c(size_t size, unsigned flags,
                                              AVRefStructOpaque opaque,
                                              int  (*init_cb)(AVRefStructOpaque opaque, void *obj),
                                              void (*reset_cb)(AVRefStructOpaque opaque, void *obj),
                                              void (*free_entry_cb)(AVRefStructOpaque opaque, void *obj),
                                              void (*free_cb)(AVRefStructOpaque opaque));

/**
* A wrapper around av_refstruct_pool_alloc_ext_c() for the common case
* of a non-const qualified opaque.
*
* @see av_refstruct_pool_alloc_ext_c()
*/
static inline
AVRefStructPool *av_refstruct_pool_alloc_ext(size_t size, unsigned flags,
                                            void *opaque,
                                            int  (*init_cb)(AVRefStructOpaque opaque, void *obj),
                                            void (*reset_cb)(AVRefStructOpaque opaque, void *obj),
                                            void (*free_entry_cb)(AVRefStructOpaque opaque, void *obj),
                                            void (*free_cb)(AVRefStructOpaque opaque))
{
   return av_refstruct_pool_alloc_ext_c(size, flags, (AVRefStructOpaque){.nc = opaque},
                                        init_cb, reset_cb, free_entry_cb, free_cb);
}

/**
* Get an object from the pool, reusing an old one from the pool when
* available.
*
* Every call to this function must happen before av_refstruct_pool_uninit().
* Otherwise undefined behaviour may occur.
*
* @param pool the pool from which to get the object
* @return a reference to the object on success, NULL on error.
*/
void *av_refstruct_pool_get(AVRefStructPool *pool);

/**
* Mark the pool as being available for freeing. It will actually be freed
* only once all the allocated buffers associated with the pool are released.
* Thus it is safe to call this function while some of the allocated buffers
* are still in use.
*
* It is illegal to try to get a new entry after this function has been called.
*
* @param poolp pointer to a pointer to either NULL or a pool to be freed.
*              `*poolp` will be set to NULL.
*/
static inline void av_refstruct_pool_uninit(AVRefStructPool **poolp)
{
   av_refstruct_unref(poolp);
}

#endif /* AVUTIL_REFSTRUCT_H */