lunaix-os/kernel/ds/rwlock.c

   1 #include <lunaix/ds/rwlock.h>
   2 #include <lunaix/spike.h>
   3
   4 void
   5 rwlock_init(rwlock_t* rwlock)
   6 {
   7     waitq_init(&rwlock->waiting_readers);
   8     waitq_init(&rwlock->waiting_writers);
   9     atomic_init(&rwlock->readers, 0);
  10     atomic_flag_clear(&rwlock->writer);
  11 }
  12
  13 void
  14 rwlock_begin_read(rwlock_t* rwlock)
  15 {
  16     while (atomic_flag_test_and_set(&rwlock->writer)) {
  17         pwait(&rwlock->waiting_readers);
  18     }
  19     atomic_fetch_add(&rwlock->readers, 1);
  20     atomic_flag_clear(&rwlock->writer);
  21     pwake_all(&rwlock->waiting_readers);
  22 }
  23
  24 void
  25 rwlock_end_read(rwlock_t* rwlock)
  26 {
  27     assert(atomic_load(&rwlock->readers) > 0);
  28     atomic_fetch_sub(&rwlock->readers, 1);
  29
  30     if (!atomic_load(&rwlock->readers)) {
  31         pwake_one(&rwlock->waiting_writers);
  32     }
  33 }
  34
  35 void
  36 rwlock_begin_write(rwlock_t* rwlock)
  37 {
  38     // first, acquire writer lock, prevent any incoming readers
  39     while (atomic_flag_test_and_set(&rwlock->writer)) {
  40         pwait(&rwlock->waiting_writers);
  41     }
  42
  43     // then, wait for reader finish the read.
  44     while (atomic_load(&rwlock->readers)) {
  45         pwait(&rwlock->waiting_writers);
  46     }
  47 }
  48
  49 void
  50 rwlock_end_write(rwlock_t* rwlock)
  51 {
  52     atomic_flag_clear(&rwlock->writer);
  53     if (waitq_empty(&rwlock->waiting_writers)) {
  54         pwake_all(&rwlock->waiting_readers);
  55     } else {
  56         pwake_one(&rwlock->waiting_writers);
  57     }
  58 }