include/vlc_atomic.h

   1 /*****************************************************************************
   2  * vlc_atomic.h:
   3  *****************************************************************************
   4  * Copyright (C) 2010 Rémi Denis-Courmont
   5  *
   6  * This program is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU Lesser General Public License as published by
   8  * the Free Software Foundation; either version 2.1 of the License, or
   9  * (at your option) any later version.
  10  *
  11  * This program is distributed in the hope that it will be useful,
  12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  14  * GNU Lesser General Public License for more details.
  15  *
  16  * You should have received a copy of the GNU Lesser General Public License
  17  * along with this program; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  19  *****************************************************************************/
  20
  21 #ifdef __cplusplus
  22 # error Not implemented in C++.
  23 #endif
  24
  25 #ifndef VLC_ATOMIC_H
  26 # define VLC_ATOMIC_H
  27
  28 /**
  29  * \file
  30  * Atomic operations do not require locking, but they are not very powerful.
  31  */
  32
  33 # include <assert.h>
  34 # include <stdatomic.h>
  35 # include <vlc_common.h>
  36
  37 typedef atomic_uint_least32_t vlc_atomic_float;
  38
  39 static inline void vlc_atomic_init_float(vlc_atomic_float *var, float f)
  40 {
  41     union { float f; uint32_t i; } u;
  42     u.f = f;
  43     atomic_init(var, u.i);
  44 }
  45
  46 /** Helper to retrieve a single precision from an atom. */
  47 static inline float vlc_atomic_load_float(vlc_atomic_float *atom)
  48 {
  49     union { float f; uint32_t i; } u;
  50     u.i = atomic_load(atom);
  51     return u.f;
  52 }
  53
  54 /** Helper to store a single precision into an atom. */
  55 static inline void vlc_atomic_store_float(vlc_atomic_float *atom, float f)
  56 {
  57     union { float f; uint32_t i; } u;
  58     u.f = f;
  59     atomic_store(atom, u.i);
  60 }
  61
  62 typedef struct vlc_atomic_rc_t {
  63     atomic_uint refs;
  64 } vlc_atomic_rc_t;
  65
  66 /** Init the RC to 1 */
  67 static inline void vlc_atomic_rc_init(vlc_atomic_rc_t *rc)
  68 {
  69     atomic_init(&rc->refs, 1);
  70 }
  71
  72 /** Increment the RC */
  73 static inline void vlc_atomic_rc_inc(vlc_atomic_rc_t *rc)
  74 {
  75     unsigned prev = atomic_fetch_add_explicit(&rc->refs, 1, memory_order_relaxed);
  76     vlc_assert(prev);
  77     VLC_UNUSED(prev);
  78 }
  79
  80 /** Decrement the RC and return true if it reaches 0 */
  81 static inline bool vlc_atomic_rc_dec(vlc_atomic_rc_t *rc)
  82 {
  83     unsigned prev = atomic_fetch_sub_explicit(&rc->refs, 1, memory_order_acq_rel);
  84     vlc_assert(prev);
  85     return prev == 1;
  86 }
  87
  88 #endif