[02/13] Add a compat stdatomic.h implementation based on GCC atomics

Message ID 1469793154-6810-2-git-send-email-anton@khirnov.net
State New
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Commit Message

Anton Khirnov July 29, 2016, 11:52 a.m.
Adapted from the code by Rémi Denis-Courmont from VLC
---
 compat/atomics/gcc/stdatomic.h | 175 +++++++++++++++++++++++++++++++++++++++++
 configure                      |   6 ++
 2 files changed, 181 insertions(+)
 create mode 100644 compat/atomics/gcc/stdatomic.h

Comments

James Almer July 29, 2016, 2:20 p.m. | #1
On 7/29/2016 8:52 AM, Anton Khirnov wrote:
> Adapted from the code by Rémi Denis-Courmont from VLC
> ---
>  compat/atomics/gcc/stdatomic.h | 175 +++++++++++++++++++++++++++++++++++++++++
>  configure                      |   6 ++
>  2 files changed, 181 insertions(+)
>  create mode 100644 compat/atomics/gcc/stdatomic.h
> 

Wouldn't it be better to use the new atomic builtins (gcc 4.7 and
newer) instead of the deprecated __sync ones? Unlike the latter 
they also support the memory order argument, so it's a much better
fit for these wrappers.

https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
Anton Khirnov July 29, 2016, 2:26 p.m. | #2
Quoting James Almer (2016-07-29 16:20:48)
> On 7/29/2016 8:52 AM, Anton Khirnov wrote:
> > Adapted from the code by Rémi Denis-Courmont from VLC
> > ---
> >  compat/atomics/gcc/stdatomic.h | 175 +++++++++++++++++++++++++++++++++++++++++
> >  configure                      |   6 ++
> >  2 files changed, 181 insertions(+)
> >  create mode 100644 compat/atomics/gcc/stdatomic.h
> > 
> 
> Wouldn't it be better to use the new atomic builtins (gcc 4.7 and
> newer) instead of the deprecated __sync ones? Unlike the latter 
> they also support the memory order argument, so it's a much better
> fit for these wrappers.
> 
> https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html

What would be the point? gcc 4.7 supports c11, so this fallback won't be
used there.
James Almer July 29, 2016, 2:35 p.m. | #3
On 7/29/2016 11:26 AM, Anton Khirnov wrote:
> Quoting James Almer (2016-07-29 16:20:48)
>> On 7/29/2016 8:52 AM, Anton Khirnov wrote:
>>> Adapted from the code by Rémi Denis-Courmont from VLC
>>> ---
>>>  compat/atomics/gcc/stdatomic.h | 175 +++++++++++++++++++++++++++++++++++++++++
>>>  configure                      |   6 ++
>>>  2 files changed, 181 insertions(+)
>>>  create mode 100644 compat/atomics/gcc/stdatomic.h
>>>
>>
>> Wouldn't it be better to use the new atomic builtins (gcc 4.7 and
>> newer) instead of the deprecated __sync ones? Unlike the latter 
>> they also support the memory order argument, so it's a much better
>> fit for these wrappers.
>>
>> https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
> 
> What would be the point? gcc 4.7 supports c11, so this fallback won't be
> used there.

According to GCC, no. stdatomic.h was added in GCC 4.9
https://gcc.gnu.org/gcc-4.9/changes.html

It's just a suggestion anyway. I guess adding a separate implementation
of this compat header for just GCC 4.7 and 4.8 (both unsupported at this
point) is probably not worth the effort.
Anton Khirnov July 29, 2016, 2:37 p.m. | #4
Quoting Anton Khirnov (2016-07-29 16:26:36)
> Quoting James Almer (2016-07-29 16:20:48)
> > On 7/29/2016 8:52 AM, Anton Khirnov wrote:
> > > Adapted from the code by Rémi Denis-Courmont from VLC
> > > ---
> > >  compat/atomics/gcc/stdatomic.h | 175 +++++++++++++++++++++++++++++++++++++++++
> > >  configure                      |   6 ++
> > >  2 files changed, 181 insertions(+)
> > >  create mode 100644 compat/atomics/gcc/stdatomic.h
> > > 
> > 
> > Wouldn't it be better to use the new atomic builtins (gcc 4.7 and
> > newer) instead of the deprecated __sync ones? Unlike the latter 
> > they also support the memory order argument, so it's a much better
> > fit for these wrappers.
> > 
> > https://gcc.gnu.org/onlinedocs/gcc/_005f_005fatomic-Builtins.html
> 
> What would be the point? gcc 4.7 supports c11, so this fallback won't be
> used there.

Ok, now I've tested it and it doesn't have stdatomic.h
Still, I wouldn't bother, since only a few versions will have those new
atomics and not have stdatomic.h

Patch

diff --git a/compat/atomics/gcc/stdatomic.h b/compat/atomics/gcc/stdatomic.h
new file mode 100644
index 0000000..bfe5bfa
--- /dev/null
+++ b/compat/atomics/gcc/stdatomic.h
@@ -0,0 +1,175 @@ 
+/*
+ * This file is part of Libav.
+ *
+ * Libav is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * Libav is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with Libav; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/*
+ * based on vlc_atomic.h from VLC
+ * Copyright (C) 2010 Rémi Denis-Courmont
+ */
+
+#ifndef STDATOMIC_H
+#define STDATOMIC_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+#define ATOMIC_FLAG_INIT 0
+
+#define ATOMIC_VAR_INIT(value) (value)
+
+#define atomic_init(obj, value) \
+do {                            \
+    *(obj) = (value);           \
+} while(0)
+
+#define kill_dependency(y) ((void)0)
+
+#define atomic_thread_fence(order) \
+    __sync_synchronize()
+
+#define atomic_signal_fence(order) \
+    ((void)0)
+
+#define atomic_is_lock_free(obj) 0
+
+typedef         _Bool      atomic_flag;
+typedef         _Bool      atomic_bool;
+typedef          char      atomic_char;
+typedef   signed char      atomic_schar;
+typedef unsigned char      atomic_uchar;
+typedef          short     atomic_short;
+typedef unsigned short     atomic_ushort;
+typedef          int       atomic_int;
+typedef unsigned int       atomic_uint;
+typedef          long      atomic_long;
+typedef unsigned long      atomic_ulong;
+typedef          long long atomic_llong;
+typedef unsigned long long atomic_ullong;
+//typedef          char16_t  atomic_char16_t;
+//typedef          char32_t  atomic_char32_t;
+typedef          wchar_t   atomic_wchar_t;
+typedef       int_least8_t atomic_int_least8_t;
+typedef      uint_least8_t atomic_uint_least8_t;
+typedef      int_least16_t atomic_int_least16_t;
+typedef     uint_least16_t atomic_uint_least16_t;
+typedef      int_least32_t atomic_int_least32_t;
+typedef     uint_least32_t atomic_uint_least32_t;
+typedef      int_least64_t atomic_int_least64_t;
+typedef     uint_least64_t atomic_uint_least64_t;
+typedef       int_fast8_t atomic_int_fast8_t;
+typedef      uint_fast8_t atomic_uint_fast8_t;
+typedef      int_fast16_t atomic_int_fast16_t;
+typedef     uint_fast16_t atomic_uint_fast16_t;
+typedef      int_fast32_t atomic_int_fast32_t;
+typedef     uint_fast32_t atomic_uint_fast32_t;
+typedef      int_fast64_t atomic_int_fast64_t;
+typedef     uint_fast64_t atomic_uint_fast64_t;
+typedef          intptr_t atomic_intptr_t;
+typedef         uintptr_t atomic_uintptr_t;
+typedef            size_t atomic_size_t;
+typedef         ptrdiff_t atomic_ptrdiff_t;
+typedef          intmax_t atomic_intmax_t;
+typedef         uintmax_t atomic_uintmax_t;
+
+#define atomic_store(object, desired)   \
+do {                                    \
+    *(object) = (desired);              \
+    __sync_synchronize();               \
+} while (0)
+
+#define atomic_store_explicit(object, desired, order) \
+    atomic_store(object, desired)
+
+#define atomic_load(object) \
+    (__sync_synchronize(), *(object))
+
+#define atomic_load_explicit(object, order) \
+    atomic_load(object)
+
+#define atomic_exchange(object, desired)                            \
+({                                                                  \
+    typeof(object) _obj = (object);                                 \
+    typeof(*object) _old;                                           \
+    do                                                              \
+        _old = atomic_load(_obj);                                   \
+    while (!__sync_bool_compare_and_swap(_obj, _old, (desired)));   \
+    _old;                                                           \
+})
+
+#define atomic_exchange_explicit(object, desired, order) \
+    atomic_exchange(object, desired)
+
+#define atomic_compare_exchange_strong(object, expected, desired)   \
+({                                                                  \
+    typeof(object) _exp = (expected);                               \
+    typeof(*object) _old = *_exp;                                   \
+    *_exp = __sync_val_compare_and_swap((object), _old, (desired)); \
+    *_exp == _old;                                                  \
+})
+
+#define atomic_compare_exchange_strong_explicit(object, expected, desired, success, failure) \
+    atomic_compare_exchange_strong(object, expected, desired)
+
+#define atomic_compare_exchange_weak(object, expected, desired) \
+    atomic_compare_exchange_strong(object, expected, desired)
+
+#define atomic_compare_exchange_weak_explicit(object, expected, desired, success, failure) \
+    atomic_compare_exchange_weak(object, expected, desired)
+
+#define atomic_fetch_add(object, operand) \
+    __sync_fetch_and_add(object, operand)
+
+#define atomic_fetch_add_explicit(object, operand, order) \
+    atomic_fetch_add(object, operand)
+
+#define atomic_fetch_sub(object, operand) \
+    __sync_fetch_and_sub(object, operand)
+
+#define atomic_fetch_sub_explicit(object, operand, order) \
+    atomic_fetch_sub(object, operand)
+
+#define atomic_fetch_or(object, operand) \
+    __sync_fetch_and_or(object, operand)
+
+#define atomic_fetch_or_explicit(object, operand, order) \
+    atomic_fetch_or(object, operand)
+
+#define atomic_fetch_xor(object, operand) \
+    __sync_fetch_and_sub(object, operand)
+
+#define atomic_fetch_xor_explicit(object, operand, order) \
+    atomic_fetch_sub(object, operand)
+
+#define atomic_fetch_and(object, operand) \
+    __sync_fetch_and_and(object, operand)
+
+#define atomic_fetch_and_explicit(object, operand, order) \
+    atomic_fetch_and(object, operand)
+
+#define atomic_flag_test_and_set(object) \
+    atomic_exchange(object, 1)
+
+#define atomic_flag_test_and_set_explicit(object, order) \
+    atomic_flag_test_and_set(object)
+
+#define atomic_flag_clear(object) \
+    atomic_store(object, 0)
+
+#define atomic_flag_clear_explicit(object, order) \
+    atomic_flag_clear(object)
+
+#endif /* STDATOMIC_H */
diff --git a/configure b/configure
index e09d366..1142543 100755
--- a/configure
+++ b/configure
@@ -5065,6 +5065,12 @@  for thread in $THREADS_LIST; do
     fi
 done
 
+if disabled stdatomic_h; then
+    if enabled atomics_gcc; then
+        add_cppflags '-I\$(SRC_PATH)/compat/atomics/gcc'
+    fi
+fi
+
 enabled zlib && add_cppflags -DZLIB_CONST
 
 # conditional library dependencies, in linking order