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 #ifndef VLC_ATOMIC_H
  22 # define VLC_ATOMIC_H
  23
  24 /**
  25  * \file
  26  * Atomic operations do not require locking, but they are not very powerful.
  27  */
  28
  29 # include <assert.h>
  30 #ifndef __cplusplus
  31 # include <stdatomic.h>
  32 #else
  33 # include <atomic>
  34 using std::atomic_uintptr_t;
  35 using std::memory_order_relaxed;
  36 using std::memory_order_acq_rel;
  37 #endif
  38 # include <vlc_common.h>
  39
  40 typedef struct vlc_atomic_rc_t {
  41     atomic_uintptr_t refs;
  42 } vlc_atomic_rc_t;
  43
  44 /** Init the RC to 1 */
  45 static inline void vlc_atomic_rc_init(vlc_atomic_rc_t *rc)
  46 {
  47     atomic_init(&rc->refs, (uintptr_t)1);
  48 }
  49
  50 /** Increment the RC */
  51 static inline void vlc_atomic_rc_inc(vlc_atomic_rc_t *rc)
  52 {
  53     uintptr_t prev = atomic_fetch_add_explicit(&rc->refs, (uintptr_t)1,
  54                                                memory_order_relaxed);
  55     vlc_assert(prev);
  56     VLC_UNUSED(prev);
  57 }
  58
  59 /** Decrement the RC and return true if it reaches 0 */
  60 static inline bool vlc_atomic_rc_dec(vlc_atomic_rc_t *rc)
  61 {
  62     uintptr_t prev = atomic_fetch_sub_explicit(&rc->refs, (uintptr_t)1,
  63                                                memory_order_acq_rel);
  64     vlc_assert(prev);
  65     return prev == 1;
  66 }
  67
  68 /** Returns the current reference count.
  69  *  This is not safe to use for logic and must only be used for debugging or
  70  *  assertion purposes */
  71 static inline uintptr_t vlc_atomic_rc_get(const vlc_atomic_rc_t* rc)
  72 {
  73     return atomic_load_explicit(&rc->refs, memory_order_relaxed);
  74 }
  75
  76 #endif