Commit b84fff07 authored by Wim Taymans's avatar Wim Taymans

memory: Require implementation to implement _share

Require the memory implementations to implement a share operation. This allows
us to remove the fallback share implementation which uses a different allocator
implementation and complicates things too much.
Update design doc a bit.
parent f6dc8eba
......@@ -50,6 +50,23 @@ Allocators
GFreeFunc free_func, gsize maxsize,
gsize offset, gsize size);
GstMemory objects are refcounted. When the GstMemory object is first created, it
has a refcount of 1.
Each variable holding a reference to the GstMemory object is responsible for
updating the refcount.
The refcount determines the writability of the object. If the refcount > 1, it is
by definition used by multipled objects and thus cannot be safely written to.
When the refcount reaches 0, and thus no objects hold a reference anymore, we
can free the memory. The GstMemoryFreeFunction of the allocator will be called
to cleanup the memory.
Memory layout
......@@ -76,10 +93,48 @@ Memory layout
void gst_memory_resize (GstMemory *mem, gsize offset, gsize size);
The visible memory region can currently only be made smaller.
The memory object is always readable. The memory block is writable when:
- the refcount is exactly 1
- the memory object has no parent, or if it has a parent, the parent is
- the memory object is not marked as READONLY.
Data Access
Access to the memory region is always controlled with a map and unmap method
call. This allows the implementation to monitor the access patterns or set up
the required memory mappings when needed.
Mapping a memory region requires the caller to specify the access method: READ
and/or WRITE. For write access, the GstMemory object must be writable.
After the data has been accessed in the object, the unmap call must be
performed. The call will update the new memory size with the specified size.
A GstMemory copy can be made with the gst_memory_copy() call. Normally,
allocators will implement a custom version of this function to make a copy of
the same kind of memory as the original one.
This is what the fallback version of the copy function will do, albeit slower
than what as custom implementation could do.
The copy operation is only required to copy the visible range of the memory
A memory region can be shared between GstMemory object with the
gst_memory_share() operation.
......@@ -87,7 +87,6 @@ static const GstMemoryAllocator *_default_allocator;
/* our predefined allocators */
static const GstMemoryAllocator *_default_mem_impl;
static const GstMemoryAllocator *_default_share_impl;
/* initialize the fields */
static void
......@@ -95,7 +94,7 @@ _default_mem_init (GstMemoryDefault * mem, GstMemoryFlags flags,
GstMemory * parent, gsize slice_size, gpointer data,
GFreeFunc free_func, gsize maxsize, gsize offset, gsize size)
mem->mem.allocator = data ? _default_mem_impl : _default_share_impl;
mem->mem.allocator = _default_mem_impl;
mem->mem.flags = flags;
mem->mem.refcount = 1;
mem->mem.parent = parent ? gst_memory_ref (parent) : NULL;
......@@ -189,22 +188,6 @@ _default_mem_map (GstMemoryDefault * mem, gsize * size, gsize * maxsize,
return mem->data + mem->offset;
static gpointer
_default_share_map (GstMemoryDefault * mem, gsize * size, gsize * maxsize,
GstMapFlags flags)
guint8 *data;
data = gst_memory_map (mem->mem.parent, size, maxsize, flags);
if (size)
*size = mem->size;
if (maxsize)
*maxsize -= mem->offset;
return data + mem->offset;
static gboolean
_default_mem_unmap (GstMemoryDefault * mem, gpointer data, gsize size)
......@@ -213,23 +196,6 @@ _default_mem_unmap (GstMemoryDefault * mem, gpointer data, gsize size)
return TRUE;
static gboolean
_default_share_unmap (GstMemoryDefault * mem, gpointer data, gsize size)
gboolean res;
guint8 *ptr = data;
if (size != -1)
mem->size = size;
size = mem->size - mem->offset;
res =
gst_memory_unmap (mem->mem.parent, ptr - mem->offset, size + mem->offset);
return res;
static void
_default_mem_free (GstMemoryDefault * mem)
......@@ -307,16 +273,6 @@ _fallback_copy (GstMemory * mem, gsize offset, gsize size)
return (GstMemory *) copy;
static GstMemory *
_fallback_share (GstMemory * mem, gsize offset, gsize size)
GstMemoryDefault *sub;
sub = _default_mem_new (0, mem, NULL, NULL, size, offset, size);
return (GstMemory *) sub;
static gboolean
_fallback_is_span (GstMemory * mem1, GstMemory * mem2, gsize * offset)
......@@ -324,7 +280,7 @@ _fallback_is_span (GstMemory * mem1, GstMemory * mem2, gsize * offset)
static GStaticRWLock lock = G_STATIC_RW_LOCK_INIT;
static GHashTable *memoryimpl;
static GHashTable *allocators;
_gst_memory_init (void)
......@@ -341,25 +297,11 @@ _gst_memory_init (void)
(GstMemoryIsSpanFunction) _default_mem_is_span,
static const GstMemoryInfo _share_info = {
(GstMemoryAllocFunction) _default_mem_alloc,
(GstMemoryGetSizesFunction) _default_mem_get_sizes,
(GstMemoryResizeFunction) _default_mem_resize,
(GstMemoryMapFunction) _default_share_map,
(GstMemoryUnmapFunction) _default_share_unmap,
(GstMemoryFreeFunction) _default_mem_free,
memoryimpl = g_hash_table_new (g_str_hash, g_str_equal);
allocators = g_hash_table_new (g_str_hash, g_str_equal);
_default_mem_impl =
gst_memory_allocator_register ("GstMemoryDefault", &_mem_info);
_default_share_impl =
gst_memory_allocator_register ("GstMemorySharebuffer", &_share_info);
_default_allocator = _default_mem_impl;
......@@ -591,7 +533,7 @@ gst_memory_is_span (GstMemory * mem1, GstMemory * mem2, gsize * offset)
* Registers the memory allocator with @name and implementation functions
* @info.
* All functions in @info are mandatory exept the copy, share and is_span
* All functions in @info are mandatory exept the copy and is_span
* functions, which will have a default implementation when left NULL.
* The user_data field in @info will be passed to all calls of the alloc
......@@ -615,19 +557,19 @@ gst_memory_allocator_register (const gchar * name, const GstMemoryInfo * info)
g_return_val_if_fail (info->map != NULL, NULL);
g_return_val_if_fail (info->unmap != NULL, NULL);
g_return_val_if_fail (info->free != NULL, NULL);
g_return_val_if_fail (info->share != NULL, NULL);
allocator = g_slice_new (GstMemoryAllocator);
allocator->name = g_quark_from_string (name);
allocator->info = *info;
GST_DEBUG ("register \"%s\" of size %" G_GSIZE_FORMAT, name);
g_static_rw_lock_writer_lock (&lock);
g_hash_table_insert (memoryimpl, (gpointer) name, (gpointer) allocator);
g_hash_table_insert (allocators, (gpointer) name, (gpointer) allocator);
g_static_rw_lock_writer_unlock (&lock);
return allocator;
......@@ -650,7 +592,7 @@ gst_memory_allocator_find (const gchar * name)
g_static_rw_lock_reader_lock (&lock);
if (name) {
allocator = g_hash_table_lookup (memoryimpl, (gconstpointer) name);
allocator = g_hash_table_lookup (allocators, (gconstpointer) name);
} else {
allocator = _default_allocator;
......@@ -130,8 +130,10 @@ GST_START_TEST (test_meta_test)
gpointer data;
buffer = gst_buffer_new_and_alloc (4);
fail_if (buffer == NULL);
data = gst_buffer_map (buffer, NULL, NULL, GST_MAP_WRITE);
fail_if (data == NULL);
memset (data, 0, 4);
gst_buffer_unmap (buffer, data, 4);
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