unlimited.txt

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

    unsigned32 allocation_size -
    
      When auto_extend is true, it is the value in the Configuration
      table and is the number of objects the object's information
      tables are extended or shrunk.

   unsigned32 size -
   
      The size of the object. It is used to calculate the size of
      memory required to be allocated when extending the table.

   unsigned32 inactive -
   
      The number of elements on the Inactive chain.

   unsigned32 *inactive_per_block -
   
      Pointer to a table of counts of the inactive objects from a
      block on the Inactive chain. It is used to know which blocks are
      all free and therefore can be returned to the heap.

   void **object_blocks -
   
      Pointer to a table of pointers to the object data. The table
      holds the pointer used to return a block to the heap when
      shrinking the object's information tables.

o Changes to Existing Object Functions

  Two functions prototypes are added. They are :

   _Objects_Extend_information,
   _Objects_Shrink_information
   _Object_Allocate, and 
   _Object_Free

  The last were inlined, how-ever now they are not as they are too
  complex to implement as macros now.

o Object Inline and Macro Changes

  The functions :

   _Object_Allocate, and 
   _Object_Free

  are now not inlined. The function :

   _Objects_Get_local_object, and
   _Objects_Set_local_object

  have been added. There was no provided interface to allow an API to
  get/set an objects local pointer given an index. The POSIX code
  should be updated to use this interface.

  The function :

   _Objects_Get_information

  has been moved to be an inline function. It is used in the get
  object call which the API uses for every object reference.

o Object Initialisation

  The function _Objects_Initialize_information has been changed to
  initialisation of the information structure's fields then call the
  new function _Objects_Extend_information.
  
  The first block of objects is always allocated and never
  released. This means with the auto-extend flag set to true the user
  still sees the same behaviour expected without this change. That is
  the number objects specified in the Configuration table is the
  number of object allocated during RTEMS initialisation. If not
  enough memory is found during this initial extend a fatal error
  occurs. The fatal error only occurs for this case of extending the
  object's information tables.

o Object Information Extend

  The _Object_Information_Extend is a new function. It takes some of
  the code form the old _Object_Initialize_information function. The
  function extends an object's information base.

  Extending the first time is a special case. The function assumes the
  maximum index will be less than the minimum index. This means the
  minimum index must be greater than 0 at initialisation. The other
  special case made is coping the tables from the old location to the
  new location. The first block case is trapped and tables are
  initialised instead. Workspace allocation for the first block is
  tested for an if the first block the allocate or fatal error call is
  made. This traps an RTEMS initialise allocation error.

  The remainder of the code deals with all cases of extending the
  object's information.

  The current block count is first determined, then a scan of the
  object_block table is made to locate a free slot. Blocks can be
  freed in any order. The index base for the block is also determined.

  If the index base is greater than the maximum index, the tables must
  grow. To grow the tables, a new larger memory block is allocated and
  the tables copied. The object's information structure is then
  updated to point to the new tables. The tables are allocated in one
  memory block from the work-space heap. The single block is then
  broken down in the required tables.

  Once the tables are copied, and the new extended parts initialised
  the table pointers in the object's information structure are
  updated. This is protected by masking interrupts.

  The old table's memory block is returned to the heap.

  The names table and object is allocated. This again is a single
  block which is divided.

  The objects are initialised onto a local Inactive chain. They are
  then copied to the object's Inactive chain to complete the
  initialisation.

o Object Informtation Shrink

  The _Object_Shrink_information function is new. It is required to
  scan all the blocks to see which one has no objects allocated. The
  last object freed might not belong to a block which is completely
  free.

  Once a block is located, the Inactive chain is interated down
  looking for objects which belong to the block of object being
  released.

  Once the Inactive chain scan is complete the names table and object
  memory is returned to the work-space heap and the table references cleared.

  XXX - I am not sure if this should occur if better protection or
  different code to provide better protection.

  The information tables do not change size. Once extended they never
  shrink.

o Object Allocation

  The _Objects_Allocate attempts to get an object from the Inactive
  chain. If auto-extend mode is not enabled no further processing
  occurs. The extra overhead for this implemetation is the function is
  not inlined and check of a boolean occurs. It should effect the
  timing figures.

  If auto-extend is enabled, a further check is made to see if the get
  from the Inactive chain suceeded in getting an object. If it failed
  a call is made to extend the object's information tables.

  The get from the Inactive chain is retried. The result of this is
  returned to the user. A failure here is the users problem.

o Object Free

  The _Objects_Free puts the object back onto the Inactive
  chain. Again if auto-extend mode is not enabled no further
  processing occurs and performance overhead will low.

  If auto-extend mode is enabled, a check is to see if the number of
  Inactive objects is one and a half times the allocation size. If
  there are that many free objects an attempt is made to shrink the
  object's information.

o Object Index and the Get Function

  The existing code allocates the number of object specified in the
  configuration table, how-ever it makes the local_table have one more
  element. This is the slot for an id of 0. The 0 slot is always a
  NULL providing a simple check for a 0 id for object classes.

  The existing _Objects_Get code removes the minimum id, which I think
  could only be 1 from the index, then adds one for the 0 slot.

  This change removes this index adjustment code in _Objects_Get.

  The extend information starts the index count when scanning for free
  blocks at the minumun index. This means the base index for a block
  will always be adjusted by the minimum index. The extend information
  function only ever allocates the allocation size of
  objects. Finially the object's local_table size is the maximum plus
  the minumum index size. The maximum is really the maximum index.

  This means the values in the object's information structure and
  tables do not need the index adjustments which existed before.

o The Test

  A new sample test, unlimited is provided. It attempts to test this
  change.