pd.if.org Git - liblfds/blob - liblfds/liblfds7.1.0/liblfds710/src/lfds710_queue_bounded_manyproducer_manyconsumer/lfds710_queue_bounded_manyproducer_manyconsumer_dequeue.c

   1 /***** includes *****/
   2 #include "lfds710_queue_bounded_manyproducer_manyconsumer_internal.h"
   3
   4
   5
   6
   7
   8 /****************************************************************************/
   9 int lfds710_queue_bmm_dequeue( struct lfds710_queue_bmm_state *qbmms,
  10                                void **key,
  11                                void **value )
  12 {
  13   char unsigned
  14     result;
  15
  16   enum lfds710_misc_flag
  17     finished_flag = LFDS710_MISC_FLAG_LOWERED;
  18
  19   int
  20     rv = 1;
  21
  22   lfds710_pal_uint_t
  23     read_index,
  24     sequence_number;
  25
  26   lfds710_pal_int_t
  27     difference;
  28
  29   lfds710_pal_uint_t
  30     backoff_iteration = LFDS710_BACKOFF_INITIAL_VALUE;
  31
  32   struct lfds710_queue_bmm_element
  33     *qbmme = NULL;
  34
  35   LFDS710_PAL_ASSERT( qbmms != NULL );
  36   // TRD : key can be NULL
  37   // TRD : value can be NULL
  38
  39   LFDS710_MISC_BARRIER_LOAD;
  40
  41   read_index = qbmms->read_index;
  42
  43   while( finished_flag == LFDS710_MISC_FLAG_LOWERED )
  44   {
  45     qbmme = &qbmms->element_array[ read_index & qbmms->mask ];
  46     LFDS710_MISC_BARRIER_LOAD;
  47     sequence_number = qbmme->sequence_number;
  48     difference = (lfds710_pal_int_t) sequence_number - (lfds710_pal_int_t) (read_index + 1);
  49
  50     if( difference == 0 )
  51     {
  52       LFDS710_PAL_ATOMIC_CAS( &qbmms->read_index, &read_index, read_index + 1, LFDS710_MISC_CAS_STRENGTH_WEAK, result );
  53       if( result == 0 )
  54         LFDS710_BACKOFF_EXPONENTIAL_BACKOFF( qbmms->dequeue_backoff, backoff_iteration );
  55       if( result == 1 )
  56         finished_flag = LFDS710_MISC_FLAG_RAISED;
  57     }
  58
  59     if( difference < 0 )
  60     {
  61       rv = 0;
  62       finished_flag = LFDS710_MISC_FLAG_RAISED;
  63     }
  64
  65     if( difference > 0 )
  66     {
  67       LFDS710_MISC_BARRIER_LOAD;
  68       read_index = qbmms->read_index;
  69     }
  70   }
  71
  72   if( rv == 1 )
  73   {
  74     if( key != NULL )
  75       *key = qbmme->key;
  76     if( value != NULL )
  77       *value = qbmme->value;
  78     LFDS710_MISC_BARRIER_STORE;
  79     qbmme->sequence_number = read_index + qbmms->mask + 1;
  80   }
  81
  82   LFDS710_BACKOFF_AUTOTUNE( qbmms->dequeue_backoff, backoff_iteration );
  83
  84   return rv;
  85 }
  86