vkmemory: don't map memory more than once

vkMapMemory may not be called on a memory object that is already
host-mapped. If the gstreamer memory object is mapped more than once then
reuse the existing Vulkan mapping.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/5917>

girs/GstVulkan-1.0.gir

@@ -4353,6 +4353,10 @@ It can be called from any thread.</doc>
         <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/vulkan/gstvkmemory.h">number of times this memory is mapped</doc>
         <type name="guint" c:type="guint"/>
       </field>
+      <field name="mapping" version="1.24" writable="1">
+        <doc xml:space="preserve" filename="../subprojects/gst-plugins-bad/gst-libs/gst/vulkan/gstvkmemory.h">internal pointer to already mapped memory</doc>
+        <type name="gpointer" c:type="gpointer"/>
+      </field>
       <field name="notify" readable="0" private="1">
         <type name="GLib.DestroyNotify" c:type="GDestroyNotify"/>
       </field>

subprojects/gst-plugins-bad/gst-libs/gst/vulkan/gstvkmemory.c

@@ -77,6 +77,8 @@ _vk_mem_init (GstVulkanMemory * mem, GstAllocator * allocator,
   mem->notify = notify;
   mem->user_data = user_data;
   mem->vk_offset = 0;
+  mem->map_count = 0;
+  mem->mapping = NULL;
 
   g_mutex_init (&mem->lock);
 
@@ -122,19 +124,29 @@ _vk_mem_map_full (GstVulkanMemory * mem, GstMapInfo * info, gsize size)
   VkResult err;
   GError *error = NULL;
 
+  g_mutex_lock (&mem->lock);
+
+  if (mem->map_count == 0) {
     if ((mem->properties & VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT) == 0) {
       GST_CAT_ERROR (GST_CAT_VULKAN_MEMORY, "Cannot map host-invisible memory");
+      g_mutex_unlock (&mem->lock);
       return NULL;
     }
 
     err = vkMapMemory (mem->device->device, mem->mem_ptr, mem->vk_offset,
-      size, 0, &data);
+        size, 0, &mem->mapping);
     if (gst_vulkan_error_to_g_error (err, &error, "vkMapMemory") < 0) {
       GST_CAT_ERROR (GST_CAT_VULKAN_MEMORY, "Failed to map device memory %s",
           error->message);
       g_clear_error (&error);
+      g_mutex_unlock (&mem->lock);
       return NULL;
     }
+  }
+
+  mem->map_count++;
+  data = mem->mapping;
+  g_mutex_unlock (&mem->lock);
 
   return data;
 }
@@ -163,7 +175,16 @@ _vk_mem_unmap_full (GstVulkanMemory * mem, GstMapInfo * info)
     }
   }
 
+  g_mutex_lock (&mem->lock);
+
+  g_assert (mem->map_count != 0);
+  mem->map_count--;
+  if (mem->map_count == 0) {
     vkUnmapMemory (mem->device->device, mem->mem_ptr);
+    mem->mapping = NULL;
+  }
+
+  g_mutex_unlock (&mem->lock);
 }
 
 static GstMemory *

subprojects/gst-plugins-bad/gst-libs/gst/vulkan/gstvkmemory.h

@@ -53,12 +53,13 @@ GType gst_vulkan_memory_allocator_get_type(void);
 #define GST_VULKAN_MEMORY_ALLOCATOR_NAME "Vulkan"
 
 /**
- * GstVulkanMemory
+ * GstVulkanMemory:
  * @mem: the parent #GstMemory
  * @device: the #GstVulkanDevice this memory is allocated from
  * @mem_ptr: the vulkan memory handle
  * @lock: lock for accessing/changing memory informat
  * @map_count: number of times this memory is mapped
+ * @mapping: internal pointer to already mapped memory
  *
  * Since: 1.18
  */
@@ -73,6 +74,14 @@ struct _GstVulkanMemory
   /* <protected> */
   GMutex                    lock;
   guint                     map_count;
+  /**
+   * GstVulkanMemory.mapping:
+   *
+   * internal pointer to already mapped memory
+   *
+   * Since: 1.24
+   */
+  gpointer                  mapping;
 
   /* <private> */
   GDestroyNotify            notify;