10 KiB
[atomics.flag]
32 Concurrency support library [thread]
32.5 Atomic operations [atomics]
32.5.10 Flag type and operations [atomics.flag]
namespace std {struct atomic_flag {constexpr atomic_flag() noexcept; atomic_flag(const atomic_flag&) = delete; atomic_flag& operator=(const atomic_flag&) = delete; atomic_flag& operator=(const atomic_flag&) volatile = delete; bool test(memory_order = memory_order::seq_cst) const volatile noexcept; constexpr bool test(memory_order = memory_order::seq_cst) const noexcept; bool test_and_set(memory_order = memory_order::seq_cst) volatile noexcept; constexpr bool test_and_set(memory_order = memory_order::seq_cst) noexcept; void clear(memory_order = memory_order::seq_cst) volatile noexcept; constexpr void clear(memory_order = memory_order::seq_cst) noexcept; void wait(bool, memory_order = memory_order::seq_cst) const volatile noexcept; constexpr void wait(bool, memory_order = memory_order::seq_cst) const noexcept; void notify_one() volatile noexcept; constexpr void notify_one() noexcept; void notify_all() volatile noexcept; constexpr void notify_all() noexcept; };}
The atomic_flag type provides the classic test-and-set functionality.
It has two states, set and clear.
Operations on an object of type atomic_flag shall be lock-free.
The operations should also be address-free.
The atomic_flag type is a standard-layout struct.
It has a trivial destructor.
constexpr atomic_flag::atomic_flag() noexcept;
Effects: Initializes *this to the clear state.
bool atomic_flag_test(const volatile atomic_flag* object) noexcept; constexpr bool atomic_flag_test(const atomic_flag* object) noexcept; bool atomic_flag_test_explicit(const volatile atomic_flag* object, memory_order order) noexcept; constexpr bool atomic_flag_test_explicit(const atomic_flag* object, memory_order order) noexcept; bool atomic_flag::test(memory_order order = memory_order::seq_cst) const volatile noexcept; constexpr bool atomic_flag::test(memory_order order = memory_order::seq_cst) const noexcept;
For atomic_flag_test, let order be memory_order::seq_cst.
Preconditions: order ismemory_order::relaxed,memory_order::acquire, ormemory_order::seq_cst.
Effects: Memory is affected according to the value of order.
Returns: Atomically returns the value pointed to by object or this.
bool atomic_flag_test_and_set(volatile atomic_flag* object) noexcept; constexpr bool atomic_flag_test_and_set(atomic_flag* object) noexcept; bool atomic_flag_test_and_set_explicit(volatile atomic_flag* object, memory_order order) noexcept; constexpr bool atomic_flag_test_and_set_explicit(atomic_flag* object, memory_order order) noexcept; bool atomic_flag::test_and_set(memory_order order = memory_order::seq_cst) volatile noexcept; constexpr bool atomic_flag::test_and_set(memory_order order = memory_order::seq_cst) noexcept;
Effects: Atomically sets the value pointed to by object or by this to true.
Memory is affected according to the value oforder.
These operations are atomic read-modify-write operations ([intro.multithread]).
Returns: Atomically, the value of the object immediately before the effects.
void atomic_flag_clear(volatile atomic_flag* object) noexcept; constexpr void atomic_flag_clear(atomic_flag* object) noexcept; void atomic_flag_clear_explicit(volatile atomic_flag* object, memory_order order) noexcept; constexpr void atomic_flag_clear_explicit(atomic_flag* object, memory_order order) noexcept; void atomic_flag::clear(memory_order order = memory_order::seq_cst) volatile noexcept; constexpr void atomic_flag::clear(memory_order order = memory_order::seq_cst) noexcept;
Preconditions: order ismemory_order::relaxed,memory_order::release, ormemory_order::seq_cst.
Effects: Atomically sets the value pointed to by object or by this tofalse.
Memory is affected according to the value of order.
void atomic_flag_wait(const volatile atomic_flag* object, bool old) noexcept; constexpr void atomic_flag_wait(const atomic_flag* object, bool old) noexcept; void atomic_flag_wait_explicit(const volatile atomic_flag* object, bool old, memory_order order) noexcept; constexpr void atomic_flag_wait_explicit(const atomic_flag* object, bool old, memory_order order) noexcept; void atomic_flag::wait(bool old, memory_order order = memory_order::seq_cst) const volatile noexcept; constexpr void atomic_flag::wait(bool old, memory_order order = memory_order::seq_cst) const noexcept;
For atomic_flag_wait, let order be memory_order::seq_cst.
Let flag be object for the non-member functions andthis for the member functions.
Preconditions: order ismemory_order::relaxed,memory_order::acquire, ormemory_order::seq_cst.
Effects: Repeatedly performs the following steps, in order:
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Evaluates flag->test(order) != old.
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If the result of that evaluation is true, returns.
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Blocks until it is unblocked by an atomic notifying operation or is unblocked spuriously.
Remarks: This function is an atomic waiting operation ([atomics.wait]).
void atomic_flag_notify_one(volatile atomic_flag* object) noexcept; constexpr void atomic_flag_notify_one(atomic_flag* object) noexcept; void atomic_flag::notify_one() volatile noexcept; constexpr void atomic_flag::notify_one() noexcept;
Effects: Unblocks the execution of at least one atomic waiting operation that is eligible to be unblocked ([atomics.wait]) by this call, if any such atomic waiting operations exist.
Remarks: This function is an atomic notifying operation ([atomics.wait]).
void atomic_flag_notify_all(volatile atomic_flag* object) noexcept; constexpr void atomic_flag_notify_all(atomic_flag* object) noexcept; void atomic_flag::notify_all() volatile noexcept; constexpr void atomic_flag::notify_all() noexcept;
Effects: Unblocks the execution of all atomic waiting operations that are eligible to be unblocked ([atomics.wait]) by this call.
Remarks: This function is an atomic notifying operation ([atomics.wait]).
#define ATOMIC_FLAG_INIT see below
Remarks: The macro ATOMIC_FLAG_INIT is defined in such a way that it can be used to initialize an object of type atomic_flag to the clear state.
The macro can be used in the form:atomic_flag guard = ATOMIC_FLAG_INIT;
It is unspecified whether the macro can be used in other initialization contexts.
For a complete static-duration object, that initialization shall be static.