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https://github.com/openvswitch/ovs
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15248032ea
We found out earlier that GCC sometimes produces an error only at link time for atomic built-ins that are not supported on a platform. This actually tries the link at configure time and should thus reliably detect whether the atomic built-ins are really supported. Signed-off-by: Ben Pfaff <blp@nicira.com> Acked-by: Ethan Jackson <ethan@nicira.com>
251 lines
8.5 KiB
C
251 lines
8.5 KiB
C
/*
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* Copyright (c) 2013 Nicira, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at:
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef OVS_ATOMIC_H
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#define OVS_ATOMIC_H 1
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/* Atomic operations.
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*
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* This library implements atomic operations with an API based on the one
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* defined in C11. It includes multiple implementations for compilers and
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* libraries with varying degrees of built-in support for C11, including an
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* fallback implementation for systems that have pthreads but no other support
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* for atomics.
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*
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* This comment describes the common features of all the implementations.
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*
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*
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* Types
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* =====
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*
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* The following atomic types are supported as typedefs for atomic versions of
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* the listed ordinary types:
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*
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* ordinary type atomic version
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* ------------------- ----------------------
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* bool atomic_bool
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*
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* char atomic_char
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* signed char atomic_schar
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* unsigned char atomic_uchar
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*
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* short atomic_short
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* unsigned short atomic_ushort
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*
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* int atomic_int
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* unsigned int atomic_uint
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*
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* long atomic_long
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* unsigned long atomic_ulong
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*
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* long long atomic_llong
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* unsigned long long atomic_ullong
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*
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* size_t atomic_size_t
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* ptrdiff_t atomic_ptrdiff_t
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*
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* intmax_t atomic_intmax_t
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* uintmax_t atomic_uintmax_t
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*
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* intptr_t atomic_intptr_t
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* uintptr_t atomic_uintptr_t
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*
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* uint8_t atomic_uint8_t (*)
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* uint16_t atomic_uint16_t (*)
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* uint32_t atomic_uint32_t (*)
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* int8_t atomic_int8_t (*)
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* int16_t atomic_int16_t (*)
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* int32_t atomic_int32_t (*)
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* uint64_t atomic_uint64_t (*)
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* int64_t atomic_int64_t (*)
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*
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* (*) Not specified by C11.
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*
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* The atomic version of a type doesn't necessarily have the same size or
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* representation as the ordinary version; for example, atomic_int might be a
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* typedef for a struct that also includes a mutex. The range of an atomic
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* type does match the range of the corresponding ordinary type.
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*
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* C11 says that one may use the _Atomic keyword in place of the typedef name,
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* e.g. "_Atomic int" instead of "atomic_int". This library doesn't support
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* that.
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*
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*
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* Initialization
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* ==============
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*
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* To initialize an atomic variable at its point of definition, use
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* ATOMIC_VAR_INIT:
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*
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* static atomic_int ai = ATOMIC_VAR_INIT(123);
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*
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* To initialize an atomic variable in code, use atomic_init():
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*
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* static atomic_int ai;
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* ...
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* atomic_init(&ai, 123);
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*
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*
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* Barriers
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* ========
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*
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* enum memory_order specifies the strictness of a memory barrier. It has the
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* following values:
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*
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* memory_order_relaxed:
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*
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* Compiler barrier only. Does not imply any CPU memory ordering.
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*
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* memory_order_acquire:
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*
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* Memory accesses after an acquire barrier cannot be moved before the
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* barrier. Memory accesses before an acquire barrier *can* be moved
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* after it.
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*
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* memory_order_release:
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*
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* Memory accesses before a release barrier cannot be moved after the
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* barrier. Memory accesses after a release barrier *can* be moved
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* before it.
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*
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* memory_order_acq_rel:
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*
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* Memory accesses cannot be moved across an acquire-release barrier in
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* either direction.
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*
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* memory_order_seq_cst:
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*
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* Prevents movement of memory accesses like an acquire-release barrier,
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* but whereas acquire-release synchronizes cooperating threads,
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* sequential-consistency synchronizes the whole system.
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*
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* memory_order_consume:
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*
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* A slight relaxation of memory_order_acquire.
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*
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* The following functions insert explicit barriers. Most of the other atomic
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* functions also include barriers.
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*
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* void atomic_thread_fence(memory_order order);
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*
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* Inserts a barrier of the specified type.
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*
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* For memory_order_relaxed, this is a no-op.
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*
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* void atomic_signal_fence(memory_order order);
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*
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* Inserts a barrier of the specified type, but only with respect to
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* signal handlers in the same thread as the barrier. This is
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* basically a compiler optimization barrier, except for
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* memory_order_relaxed, which is a no-op.
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*
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*
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* Atomic Operations
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* =================
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*
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* In this section, A is an atomic type and C is the corresponding non-atomic
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* type.
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*
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* The "store" primitives match C11:
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*
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* void atomic_store(A *object, C value);
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* void atomic_store_explicit(A *object, C value, memory_order);
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*
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* Atomically stores 'value' into '*object', respecting the given
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* memory order (or memory_order_seq_cst for atomic_store()).
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*
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* The following primitives differ from the C11 ones (and have different names)
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* because there does not appear to be a way to implement the standard
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* primitives in standard C:
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*
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* void atomic_read(A *src, C *dst);
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* void atomic_read_explicit(A *src, C *dst, memory_order);
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*
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* Atomically loads a value from 'src', writing the value read into
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* '*dst', respecting the given memory order (or memory_order_seq_cst
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* for atomic_read()).
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*
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* void atomic_add(A *rmw, C arg, C *orig);
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* void atomic_sub(A *rmw, C arg, C *orig);
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* void atomic_or(A *rmw, C arg, C *orig);
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* void atomic_xor(A *rmw, C arg, C *orig);
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* void atomic_and(A *rmw, C arg, C *orig);
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* void atomic_add_explicit(A *rmw, C arg, C *orig, memory_order);
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* void atomic_sub_explicit(A *rmw, C arg, C *orig, memory_order);
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* void atomic_or_explicit(A *rmw, C arg, C *orig, memory_order);
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* void atomic_xor_explicit(A *rmw, C arg, C *orig, memory_order);
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* void atomic_and_explicit(A *rmw, C arg, C *orig, memory_order);
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*
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* Atomically applies the given operation, with 'arg' as the second
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* operand, to '*rmw', and stores the original value of '*rmw' into
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* '*orig', respecting the given memory order (or memory_order_seq_cst
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* if none is specified).
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*
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* The results are similar to those that would be obtained with +=, -=,
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* |=, ^=, or |= on non-atomic types.
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*
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*
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* atomic_flag
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* ===========
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*
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* atomic_flag is a typedef for a type with two states, set and clear, that
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* provides atomic test-and-set functionality.
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*
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* ATOMIC_FLAG_INIT is an initializer for atomic_flag. The initial state is
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* "clear".
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*
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* The following functions are available.
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*
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* bool atomic_flag_test_and_set(atomic_flag *object)
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* bool atomic_flag_test_and_set_explicit(atomic_flag *object,
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* memory_order);
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*
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* Atomically sets '*object', respsecting the given memory order (or
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* memory_order_seq_cst for atomic_flag_test_and_set()). Returns the
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* previous value of the flag (false for clear, true for set).
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*
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* void atomic_flag_clear(atomic_flag *object);
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* void atomic_flag_clear_explicit(atomic_flag *object, memory_order);
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*
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* Atomically clears '*object', respecting the given memory order (or
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* memory_order_seq_cst for atomic_flag_clear()).
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*/
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#include <limits.h>
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#include <pthread.h>
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#include <stdbool.h>
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#include <stddef.h>
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#include <stdint.h>
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#include "compiler.h"
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#include "util.h"
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#define IN_OVS_ATOMIC_H
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#if __CHECKER__
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/* sparse doesn't understand some GCC extensions we use. */
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#include "ovs-atomic-pthreads.h"
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#elif HAVE_STDATOMIC_H
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#include "ovs-atomic-c11.h"
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#elif __GNUC__ >= 4 && __GNUC_MINOR__ >= 7
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#include "ovs-atomic-gcc4.7+.h"
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#elif HAVE_GCC4_ATOMICS
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#include "ovs-atomic-gcc4+.h"
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#else
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#include "ovs-atomic-pthreads.h"
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#endif
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#undef IN_OVS_ATOMIC_H
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#endif /* ovs-atomic.h */
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