QAtomicInteger 类

template <typename T> class QAtomicInteger

QAtomicInteger类为整数提供独立于平台的原子操作。 更多...

头：	#include <QAtomicInteger>
CMake:	find_package(Qt6 REQUIRED COMPONENTS Core) target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake:	QT += core
继承者：	QAtomicInt

• 所有成员列表，包括继承成员
• QAtomicInteger is part of 线程类 .

公共函数

	QAtomicInteger (T value = 0)
	QAtomicInteger (const QAtomicInteger<T> & other )
bool	deref ()
T	fetchAndAddAcquire (T valueToAdd )
T	fetchAndAddOrdered (T valueToAdd )
T	fetchAndAddRelaxed (T valueToAdd )
T	fetchAndAddRelease (T valueToAdd )
T	fetchAndAndAcquire (T valueToAnd )
T	fetchAndAndOrdered (T valueToAnd )
T	fetchAndAndRelaxed (T valueToAnd )
T	fetchAndAndRelease (T valueToAnd )
T	fetchAndOrAcquire (T valueToOr )
T	fetchAndOrOrdered (T valueToOr )
T	fetchAndOrRelaxed (T valueToOr )
T	fetchAndOrRelease (T valueToOr )
T	fetchAndStoreAcquire (T newValue )
T	fetchAndStoreOrdered (T newValue )
T	fetchAndStoreRelaxed (T newValue )
T	fetchAndStoreRelease (T newValue )
T	fetchAndSubAcquire (T valueToSub )
T	fetchAndSubOrdered (T valueToSub )
T	fetchAndSubRelaxed (T valueToSub )
T	fetchAndSubRelease (T valueToSub )
T	fetchAndXorAcquire (T valueToXor )
T	fetchAndXorOrdered (T valueToXor )
T	fetchAndXorRelaxed (T valueToXor )
T	fetchAndXorRelease (T valueToXor )
T	loadAcquire () const
T	loadRelaxed () const
bool	ref ()
void	storeRelaxed (T newValue )
void	storeRelease (T newValue )
bool	testAndSetAcquire (T expectedValue , T newValue )
bool	testAndSetAcquire (T expectedValue , T newValue , T & currentValue )
bool	testAndSetOrdered (T expectedValue , T newValue )
bool	testAndSetOrdered (T expectedValue , T newValue , T & currentValue )
bool	testAndSetRelaxed (T expectedValue , T newValue )
bool	testAndSetRelaxed (T expectedValue , T newValue , T & currentValue )
bool	testAndSetRelease (T expectedValue , T newValue )
bool	testAndSetRelease (T expectedValue , T newValue , T & currentValue )
T	operator T () const
T	operator&= (T value )
T	operator++ ()
T	operator++ (int)
T	operator+= (T value )
T	operator-- ()
T	operator-- (int)
T	operator-= (T value )
QAtomicInteger<T> &	operator= (const QAtomicInteger<T> & other )
QAtomicInteger<T> &	operator= (T)
T	operator^= (T value )
T	operator|= (T value )

静态公共成员

bool	isFetchAndAddNative ()
bool	isFetchAndAddWaitFree ()
bool	isFetchAndStoreNative ()
bool	isFetchAndStoreWaitFree ()
bool	isReferenceCountingNative ()
bool	isReferenceCountingWaitFree ()
bool	isTestAndSetNative ()
bool	isTestAndSetWaitFree ()

相关非成员

(从 6.7 起) void

qYieldCpu ()

宏

	Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_ALWAYS_NATIVE
	Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_NOT_NATIVE
	Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_SOMETIMES_NATIVE
	Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_WAIT_FREE
	Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_ALWAYS_NATIVE
	Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_NOT_NATIVE
	Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_SOMETIMES_NATIVE
	Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_WAIT_FREE
	Q_ATOMIC_INTnn_IS_SUPPORTED
	Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_ALWAYS_NATIVE
	Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_NOT_NATIVE
	Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_SOMETIMES_NATIVE
	Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_WAIT_FREE
	Q_ATOMIC_INTnn_TEST_AND_SET_IS_ALWAYS_NATIVE
	Q_ATOMIC_INTnn_TEST_AND_SET_IS_NOT_NATIVE
	Q_ATOMIC_INTnn_TEST_AND_SET_IS_SOMETIMES_NATIVE
	Q_ATOMIC_INTnn_TEST_AND_SET_IS_WAIT_FREE

详细描述

有关指针的原子操作，见 QAtomicPointer 类。

An atomic operation is a complex operation that completes without interruption. The QAtomicInteger class provides atomic reference counting, test-and-set, fetch-and-store, and fetch-and-add for integers.

模板参数 T 必须是 C++ 整数类型：

• 8-bit: bool, char, signed char, unsigned char, qint8, quint8, char8_t (C++20)
• 16-bit: short, unsigned short, qint16, quint16, char16_t
• 32-bit: int, unsigned int, qint32, quint32, char32_t
• 64-bit: long long, unsigned long long, qint64, quint64
• platform-specific size: long, unsigned long
• pointer size: qintptr, quintptr, qptrdiff

Of the list above, only the 8-bit, 16-bit, 32-bit- and pointer-sized instantiations are guaranteed to work on all platforms. Support for other sizes depends on the compiler and processor architecture the code is being compiled for. To test whether the 64-bit types are supported on 32-bit platforms, check the macro Q_ATOMIC_INT64_IS_SUPPORTED .

原子 API

引用计数

The ref () 和 deref () functions provide an efficient reference counting API. The return value of these functions are used to indicate when the last reference has been released. These functions allow you to implement your own implicitly shared classes.

MySharedType &MySharedType::operator=(const MySharedType &other)
{
    (void) other.data->atomicInt.ref();
    if (!data->atomicInt.deref()) {
        // The last reference has been released
        delete d;
    }
    d = other.d;
    return *this;
}
					

内存排序

QAtomicInteger provides several implementations of the atomic test-and-set, fetch-and-store, and fetch-and-add functions. Each implementation defines a memory ordering semantic that describes how memory accesses surrounding the atomic instruction are executed by the processor. Since many modern architectures allow out-of-order execution and memory ordering, using the correct semantic is necessary to ensure that your application functions properly on all processors.

• Relaxed - memory ordering is unspecified, leaving the compiler and processor to freely reorder memory accesses.
• Acquire - memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.
• Release - memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.
• Ordered - the same Acquire and Release semantics combined.

测试和设置

If the current value of the QAtomicInteger is an expected value, the test-and-set functions assign a new value to the QAtomicInteger and return true. If values are not the same, these functions do nothing and return false. This operation equates to the following code:

if (currentValue == expectedValue) {
    currentValue = newValue;
    return true;
}
return false;
					

There are 4 test-and-set functions: testAndSetRelaxed (), testAndSetAcquire (), testAndSetRelease ()，和 testAndSetOrdered (). See above for an explanation of the different memory ordering semantics.

抓取和存储

The atomic fetch-and-store functions read the current value of the QAtomicInteger and then assign a new value, returning the original value. This operation equates to the following code:

int originalValue = currentValue;
currentValue = newValue;
return originalValue;
					

There are 4 fetch-and-store functions: fetchAndStoreRelaxed (), fetchAndStoreAcquire (), fetchAndStoreRelease ()，和 fetchAndStoreOrdered (). See above for an explanation of the different memory ordering semantics.

抓取和添加

The atomic fetch-and-add functions read the current value of the QAtomicInteger and then add the given value to the current value, returning the original value. This operation equates to the following code:

int originalValue = currentValue;
currentValue += valueToAdd;
return originalValue;
					

There are 4 fetch-and-add functions: fetchAndAddRelaxed (), fetchAndAddAcquire (), fetchAndAddRelease ()，和 fetchAndAddOrdered (). See above for an explanation of the different memory ordering semantics.

用于原子 API 的特征测试

Providing a platform-independent atomic API that works on all processors is challenging. The API provided by QAtomicInteger is guaranteed to work atomically on all processors. However, since not all processors implement support for every operation provided by QAtomicInteger, it is necessary to expose information about the processor.

You can check at compile time which features are supported on your hardware using various macros. These will tell you if your hardware always, sometimes, or does not support a particular operation. The macros have the form Q_ATOMIC_INT nn _ OPERATION _IS_ HOW _NATIVE. nn is the size of the integer (in bits), OPERATION 是某一 REFERENCE_COUNTING , TEST_AND_SET , FETCH_AND_STORE ，或 FETCH_AND_ADD ，和 HOW is one of ALWAYS, SOMETIMES, or NOT. There will always be exactly one defined macro per operation. For example, if Q_ATOMIC_INT32_REFERENCE_COUNTING_IS_ALWAYS_NATIVE is defined, neither Q_ATOMIC_INT_REFERENCE_COUNTING_IS_SOMETIMES_NATIVE nor Q_ATOMIC_INT32_REFERENCE_COUNTING_IS_NOT_NATIVE will be defined.

An operation that completes in constant time is said to be wait-free. Such operations are not implemented using locks or loops of any kind. For atomic operations that are always supported, and that are wait-free, Qt defines the Q_ATOMIC_INT nn _ OPERATION _IS_WAIT_FREE in addition to the Q_ATOMIC_INT nn _ OPERATION _IS_ALWAYS_NATIVE.

In cases where an atomic operation is only supported in newer generations of the processor, QAtomicInteger also provides a way to check at runtime what your hardware supports with the isReferenceCountingNative (), isTestAndSetNative (), isFetchAndStoreNative ()，和 isFetchAndAddNative () functions. Wait-free implementations can be detected using the isReferenceCountingWaitFree (), isTestAndSetWaitFree (), isFetchAndStoreWaitFree ()，和 isFetchAndAddWaitFree () 函数。

Below is a complete list of all feature macros for QAtomicInteger:

• Q_ATOMIC_INT nn _REFERENCE_COUNTING_IS_ALWAYS_NATIVE
• Q_ATOMIC_INT nn _REFERENCE_COUNTING_IS_SOMETIMES_NATIVE
• Q_ATOMIC_INT nn _REFERENCE_COUNTING_IS_NOT_NATIVE
• Q_ATOMIC_INT nn _REFERENCE_COUNTING_IS_WAIT_FREE
• Q_ATOMIC_INT nn _TEST_AND_SET_IS_ALWAYS_NATIVE
• Q_ATOMIC_INT nn _TEST_AND_SET_IS_SOMETIMES_NATIVE
• Q_ATOMIC_INT nn _TEST_AND_SET_IS_NOT_NATIVE
• Q_ATOMIC_INT nn _TEST_AND_SET_IS_WAIT_FREE
• Q_ATOMIC_INT nn _FETCH_AND_STORE_IS_ALWAYS_NATIVE
• Q_ATOMIC_INT nn _FETCH_AND_STORE_IS_SOMETIMES_NATIVE
• Q_ATOMIC_INT nn _FETCH_AND_STORE_IS_NOT_NATIVE
• Q_ATOMIC_INT nn _FETCH_AND_STORE_IS_WAIT_FREE
• Q_ATOMIC_INT nn _FETCH_AND_ADD_IS_ALWAYS_NATIVE
• Q_ATOMIC_INT nn _FETCH_AND_ADD_IS_SOMETIMES_NATIVE
• Q_ATOMIC_INT nn _FETCH_AND_ADD_IS_NOT_NATIVE
• Q_ATOMIC_INT nn _FETCH_AND_ADD_IS_WAIT_FREE

For compatibility with previous versions of Qt, macros with an empty nn are equivalent to the 32-bit macros. For example, Q_ATOMIC_INT_REFERENCE_COUNTING_IS_WAIT_FREE is the same as Q_ATOMIC_INT32_REFERENCE_COUNTING_IS_WAIT_FREE.

另请参阅 QAtomicPointer .

成员函数文档编制

[constexpr noexcept] QAtomicInteger:: QAtomicInteger ( T value = 0)

构造 QAtomicInteger 采用给定 value .

[noexcept] QAtomicInteger:: QAtomicInteger (const QAtomicInteger < T > & other )

构造副本为 other .

bool QAtomicInteger:: deref ()

Atomically decrements the value of this QAtomicInteger 。返回 true 若新值非零，否则 false。

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 ref () 和 operator-- ().

T QAtomicInteger:: fetchAndAddAcquire ( T valueToAdd )

原子抓取和添加。

Reads the current value of this QAtomicInteger and then adds valueToAdd to the current value, returning the original value.

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

另请参阅 operator+= () 和 fetchAndSubAcquire ().

T QAtomicInteger:: fetchAndAddOrdered ( T valueToAdd )

原子抓取和添加。

Reads the current value of this QAtomicInteger and then adds valueToAdd to the current value, returning the original value.

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 operator+= () 和 fetchAndSubOrdered ().

T QAtomicInteger:: fetchAndAddRelaxed ( T valueToAdd )

原子抓取和添加。

Reads the current value of this QAtomicInteger and then adds valueToAdd to the current value, returning the original value.

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

另请参阅 operator+= () 和 fetchAndSubRelaxed ().

T QAtomicInteger:: fetchAndAddRelease ( T valueToAdd )

原子抓取和添加。

Reads the current value of this QAtomicInteger and then adds valueToAdd to the current value, returning the original value.

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

另请参阅 operator+= () 和 fetchAndSubRelease ().

T QAtomicInteger:: fetchAndAndAcquire ( T valueToAnd )

原子抓取和和。

Reads the current value of this QAtomicInteger and then bitwise-ANDs valueToAnd to the current value, returning the original value.

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

另请参阅 operator&= ().

T QAtomicInteger:: fetchAndAndOrdered ( T valueToAnd )

原子抓取和和。

Reads the current value of this QAtomicInteger and then bitwise-ANDs valueToAnd to the current value, returning the original value.

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 operator&= ().

T QAtomicInteger:: fetchAndAndRelaxed ( T valueToAnd )

原子抓取和和。

Reads the current value of this QAtomicInteger and then bitwise-ANDs valueToAnd to the current value, returning the original value.

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

另请参阅 operator&= ().

T QAtomicInteger:: fetchAndAndRelease ( T valueToAnd )

原子抓取和和。

Reads the current value of this QAtomicInteger and then bitwise-ANDs valueToAnd to the current value, returning the original value.

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

另请参阅 operator&= ().

T QAtomicInteger:: fetchAndOrAcquire ( T valueToOr )

原子抓取和或。

Reads the current value of this QAtomicInteger and then bitwise-ORs valueToOr to the current value, returning the original value.

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

另请参阅 operator|= ().

T QAtomicInteger:: fetchAndOrOrdered ( T valueToOr )

原子抓取和或。

Reads the current value of this QAtomicInteger and then bitwise-ORs valueToOr to the current value, returning the original value.

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 operator|= ().

T QAtomicInteger:: fetchAndOrRelaxed ( T valueToOr )

原子抓取和或。

Reads the current value of this QAtomicInteger and then bitwise-ORs valueToOr to the current value, returning the original value.

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

另请参阅 operator|= ().

T QAtomicInteger:: fetchAndOrRelease ( T valueToOr )

原子抓取和或。

Reads the current value of this QAtomicInteger and then bitwise-ORs valueToOr to the current value, returning the original value.

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

另请参阅 operator|= ().

T QAtomicInteger:: fetchAndStoreAcquire ( T newValue )

原子抓取和存储。

Reads the current value of this QAtomicInteger and then assigns it the newValue , returning the original value.

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

T QAtomicInteger:: fetchAndStoreOrdered ( T newValue )

原子抓取和存储。

Reads the current value of this QAtomicInteger and then assigns it the newValue , returning the original value.

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

T QAtomicInteger:: fetchAndStoreRelaxed ( T newValue )

原子抓取和存储。

Reads the current value of this QAtomicInteger and then assigns it the newValue , returning the original value.

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

T QAtomicInteger:: fetchAndStoreRelease ( T newValue )

原子抓取和存储。

Reads the current value of this QAtomicInteger and then assigns it the newValue , returning the original value.

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

T QAtomicInteger:: fetchAndSubAcquire ( T valueToSub )

Atomic fetch-and-sub.

Reads the current value of this QAtomicInteger and then subtracts valueToSub to the current value, returning the original value.

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

另请参阅 operator-= () 和 fetchAndAddAcquire ().

T QAtomicInteger:: fetchAndSubOrdered ( T valueToSub )

Atomic fetch-and-sub.

Reads the current value of this QAtomicInteger and then subtracts valueToSub to the current value, returning the original value.

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 operator-= () 和 fetchAndAddOrdered ().

T QAtomicInteger:: fetchAndSubRelaxed ( T valueToSub )

Atomic fetch-and-sub.

Reads the current value of this QAtomicInteger and then subtracts valueToSub to the current value, returning the original value.

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

另请参阅 operator-= () 和 fetchAndAddRelaxed ().

T QAtomicInteger:: fetchAndSubRelease ( T valueToSub )

Atomic fetch-and-sub.

Reads the current value of this QAtomicInteger and then subtracts valueToSub to the current value, returning the original value.

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

另请参阅 operator-= () 和 fetchAndAddRelease ().

T QAtomicInteger:: fetchAndXorAcquire ( T valueToXor )

Atomic fetch-and-xor.

Reads the current value of this QAtomicInteger and then bitwise-XORs valueToXor to the current value, returning the original value.

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

另请参阅 operator^= ().

T QAtomicInteger:: fetchAndXorOrdered ( T valueToXor )

Atomic fetch-and-xor.

Reads the current value of this QAtomicInteger and then bitwise-XORs valueToXor to the current value, returning the original value.

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 operator^= ().

T QAtomicInteger:: fetchAndXorRelaxed ( T valueToXor )

Atomic fetch-and-xor.

Reads the current value of this QAtomicInteger and then bitwise-XORs valueToXor to the current value, returning the original value.

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

另请参阅 operator^= ().

T QAtomicInteger:: fetchAndXorRelease ( T valueToXor )

Atomic fetch-and-xor.

Reads the current value of this QAtomicInteger and then bitwise-XORs valueToXor to the current value, returning the original value.

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

另请参阅 operator^= ().

[static constexpr] bool QAtomicInteger:: isFetchAndAddNative ()

返回 true if fetch-and-add is implemented using atomic processor instructions, false otherwise.

[static constexpr] bool QAtomicInteger:: isFetchAndAddWaitFree ()

返回 true if atomic fetch-and-add is wait-free, false otherwise.

[static constexpr] bool QAtomicInteger:: isFetchAndStoreNative ()

返回 true if fetch-and-store is implemented using atomic processor instructions, false otherwise.

[static constexpr] bool QAtomicInteger:: isFetchAndStoreWaitFree ()

返回 true if atomic fetch-and-store is wait-free, false otherwise.

[static constexpr] bool QAtomicInteger:: isReferenceCountingNative ()

返回 true if reference counting is implemented using atomic processor instructions, false otherwise.

[static constexpr] bool QAtomicInteger:: isReferenceCountingWaitFree ()

返回 true if atomic reference counting is wait-free, false otherwise.

[static constexpr] bool QAtomicInteger:: isTestAndSetNative ()

返回 true if test-and-set is implemented using atomic processor instructions, false otherwise.

[static constexpr] bool QAtomicInteger:: isTestAndSetWaitFree ()

返回 true if atomic test-and-set is wait-free, false otherwise.

T QAtomicInteger:: loadAcquire () const

Atomically loads the value of this QAtomicInteger using the "Acquire" memory ordering. The value is not modified in any way, but note that there's no guarantee that it remains so.

另请参阅 storeRelaxed () 和 loadRelaxed ().

T QAtomicInteger:: loadRelaxed () const

Atomically loads the value of this QAtomicInteger using relaxed memory ordering. The value is not modified in any way, but note that there's no guarantee that it remains so.

另请参阅 storeRelaxed () 和 loadAcquire ().

bool QAtomicInteger:: ref ()

Atomically increments the value of this QAtomicInteger 。返回 true 若新值非零，否则 false。

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

另请参阅 deref () 和 operator++ ().

void QAtomicInteger:: storeRelaxed ( T newValue )

Atomically stores the newValue value into this atomic type, using relaxed memory ordering.

另请参阅 storeRelease () 和 loadRelaxed ().

void QAtomicInteger:: storeRelease ( T newValue )

Atomically stores the newValue value into this atomic type, using the "Release" memory ordering.

另请参阅 storeRelaxed () 和 loadAcquire ().

bool QAtomicInteger:: testAndSetAcquire ( T expectedValue , T newValue )

Atomic test-and-set.

注意： If you use this function in a loop, consider using the overload with the additional T ¤tValue argument instead, which avoids the extra load() on failure.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger and return true. If the values are not the same, this function does nothing and returns false .

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

bool QAtomicInteger:: testAndSetAcquire ( T expectedValue , T newValue , T & currentValue )

Atomic test-and-set.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger 并返回 true . If the values are not the same, the functions load the current value of this QAtomicInteger into currentValue 并返回 false .

此函数使用 acquire memory ordering semantics, which ensures that memory access following the atomic operation (in program order) may not be re-ordered before the atomic operation.

bool QAtomicInteger:: testAndSetOrdered ( T expectedValue , T newValue )

Atomic test-and-set.

注意： If you use this function in a loop, consider using the overload with the additional T ¤tValue argument instead, which avoids the extra load() on failure.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger and return true. If the values are not the same, this function does nothing and returns false .

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

bool QAtomicInteger:: testAndSetOrdered ( T expectedValue , T newValue , T & currentValue )

Atomic test-and-set.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger 并返回 true . If the values are not the same, it loads the current value of this QAtomicInteger into currentValue 并返回 false .

此函数使用 ordered memory ordering semantics, which ensures that memory access before and after the atomic operation (in program order) may not be re-ordered.

bool QAtomicInteger:: testAndSetRelaxed ( T expectedValue , T newValue )

Atomic test-and-set.

注意： If you use this function in a loop, consider using the overload with the additional T ¤tValue argument instead, which avoids the extra load() on failure.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger and return true. If the values are not the same, this function does nothing and returns false .

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

bool QAtomicInteger:: testAndSetRelaxed ( T expectedValue , T newValue , T & currentValue )

Atomic test-and-set.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger 并返回 true . If the values are not the same, the functions load the current value of this QAtomicInteger into currentValue 并返回 false .

此函数使用 relaxed memory ordering semantics, leaving the compiler and processor to freely reorder memory accesses.

bool QAtomicInteger:: testAndSetRelease ( T expectedValue , T newValue )

Atomic test-and-set.

注意： If you use this function in a loop, consider using the overload with the additional T ¤tValue argument instead, which avoids the extra load() on failure.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger and return true. If the values are not the same, this function does nothing and returns false .

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

bool QAtomicInteger:: testAndSetRelease ( T expectedValue , T newValue , T & currentValue )

Atomic test-and-set.

If the current value of this QAtomicInteger 是 expectedValue , the test-and-set functions assign the newValue 到此 QAtomicInteger 并返回 true . If the values are not the same, the functions loads the current value of this QAtomicInteger into currentValue 并返回 false .

此函数使用 release memory ordering semantics, which ensures that memory access before the atomic operation (in program order) may not be re-ordered after the atomic operation.

T QAtomicInteger:: operator T () const

Atomically loads the value of this QAtomicInteger using a sequentially consistent memory ordering if possible; or "Acquire" ordering if not. The value is not modified in any way, but note that there's no guarantee that it remains so.

另请参阅 loadRelaxed () 和 loadAcquire ().

T QAtomicInteger:: operator&= ( T value )

Atomic add-and-fetch.

Reads the current value of this QAtomicInteger and then bitwise-ANDs value to the current value, returning the new value.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 fetchAndAndOrdered ().

T QAtomicInteger:: operator++ ()

Atomically pre-increments the value of this QAtomicInteger . Returns the new value of this atomic.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 ref (), operator++ (int), and operator-- ().

T QAtomicInteger:: operator++ ( int )

Atomically post-increments the value of this QAtomicInteger . Returns the old value of this atomic.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 ref (), operator++ ()，和 operator-- (int).

T QAtomicInteger:: operator+= ( T value )

Atomic add-and-fetch.

Reads the current value of this QAtomicInteger and then adds value to the current value, returning the new value.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 fetchAndAddOrdered () 和 operator-= ().

T QAtomicInteger:: operator-- ()

Atomically pre-decrements the value of this QAtomicInteger . Returns the new value of this atomic.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 deref (), operator-- (int), and operator++ ().

T QAtomicInteger:: operator-- ( int )

Atomically post-decrements the value of this QAtomicInteger . Returns the old value of this atomic.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 deref (), operator-- ()，和 operator++ (int).

T QAtomicInteger:: operator-= ( T value )

Atomic sub-and-fetch.

Reads the current value of this QAtomicInteger and then subtracts value to the current value, returning the new value.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 fetchAndSubOrdered () 和 operator+= ().

[noexcept] QAtomicInteger < T > &QAtomicInteger:: operator= (const QAtomicInteger < T > & other )

赋值 other 到此 QAtomicInteger and returns a reference to this QAtomicInteger .

QAtomicInteger < T > &QAtomicInteger:: operator= ( T )

Atomically stores the other value into this atomic type using a sequentially consistent memory ordering if possible; or "Release" ordering if not. This function returns a reference to this object.

另请参阅 storeRelaxed () 和 storeRelease ().

T QAtomicInteger:: operator^= ( T value )

Atomic xor-and-fetch.

Reads the current value of this QAtomicInteger and then bitwise-XORs value to the current value, returning the new value.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 fetchAndXorOrdered ().

T QAtomicInteger:: operator|= ( T value )

Atomic or-and-fetch.

Reads the current value of this QAtomicInteger and then bitwise-ORs value to the current value, returning the new value.

This function uses a sequentially consistent memory ordering if possible; or "Ordered" ordering if not.

另请参阅 fetchAndOrOrdered ().

相关非成员

[noexcept, since 6.7] void qYieldCpu ()

Pauses the execution of the current thread for an unspecified time, using hardware instructions, without de-scheduling this thread. This function is meant to be used in high-throughput loops where the code expects another thread to modify an atomic variable. This is completely different from QThread::yieldCurrentThread (), which is an OS-level operation that may take the whole thread off the CPU and allow other threads (possibly belonging to other processes) to run.

So, instead of

while (!condition)
    ;
					

one should write

while (!condition)
    qYieldCpu();
					

This is useful both with and without hardware multithreading on the same core. In the case of hardware threads, it serves to prevent further speculative execution filling up the pipeline, which could starve the sibling thread of resources. Across cores and higher levels of separation, it allows the cache coherency protocol to allocate the cache line being modified and inspected to the logical processor whose result this code is expecting.

It is also recommended to loop around code that does not modify the global variable, to avoid contention in exclusively obtaining the memory location. Therefore, an atomic modification loop such as a spinlock acquisition should be:

while (true) {
    while (!readOnlyCondition(atomic))
        qYieldCpu();
    if (modify(atomic))
        break;
}
					

On x86 processors and on RISC-V processors with the Zihintpause extension, this will emit the PAUSE instruction, which is ignored on processors that don't support it; on ARMv7 or later ARM processors, it will emit the YIELD instruction.

该函数在 Qt 6.7 引入。

宏文档编制

Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_ALWAYS_NATIVE

This macro is defined if and only if your processor supports atomic fetch-and-add on integers.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_NOT_NATIVE

This macro is defined when the hardware does not support atomic fetch-and-add on integers.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_SOMETIMES_NATIVE

This macro is defined when only certain generations of the processor support atomic fetch-and-add on integers. Use the QAtomicInteger <T>::isFetchAndAddNative() function to check what your processor supports.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_WAIT_FREE

This macro is defined together with Q_ATOMIC_INTnn_FETCH_AND_ADD_IS_ALWAYS_NATIVE to indicate that the atomic fetch-and-add on integers is wait-free.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_ALWAYS_NATIVE

This macro is defined if and only if your processor supports atomic fetch-and-store on integers.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_NOT_NATIVE

This macro is defined when the hardware does not support atomic fetch-and-store on integers.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_SOMETIMES_NATIVE

This macro is defined when only certain generations of the processor support atomic fetch-and-store on integers. Use the QAtomicInteger <T>::isFetchAndStoreNative() function to check what your processor supports.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_WAIT_FREE

This macro is defined together with Q_ATOMIC_INTnn_FETCH_AND_STORE_IS_ALWAYS_NATIVE to indicate that the atomic fetch-and-store on integers is wait-free.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_IS_SUPPORTED

This macro is defined if atomic integers of size nn (in bits) are supported in this compiler / architecture combination.

nn is the size of the integer, in bits (8, 16, 32 or 64).

The following macros always defined:

• Q_ATOMIC_INT8_IS_SUPPORTED
• Q_ATOMIC_INT16_IS_SUPPORTED
• Q_ATOMIC_INT32_IS_SUPPORTED

Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_ALWAYS_NATIVE

This macro is defined if and only if all generations of your processor support atomic reference counting.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_NOT_NATIVE

This macro is defined when the hardware does not support atomic reference counting.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_SOMETIMES_NATIVE

This macro is defined when only certain generations of the processor support atomic reference counting. Use the QAtomicInteger <T>::isReferenceCountingNative() function to check what your processor supports.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_WAIT_FREE

This macro is defined together with Q_ATOMIC_INTnn_REFERENCE_COUNTING_IS_ALWAYS_NATIVE to indicate that the reference counting is wait-free.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_TEST_AND_SET_IS_ALWAYS_NATIVE

This macro is defined if and only if your processor supports atomic test-and-set on integers.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_TEST_AND_SET_IS_NOT_NATIVE

This macro is defined when the hardware does not support atomic test-and-set on integers.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_TEST_AND_SET_IS_SOMETIMES_NATIVE

This macro is defined when only certain generations of the processor support atomic test-and-set on integers. Use the QAtomicInteger <T>::isTestAndSetNative() function to check what your processor supports.

nn is the size of the integer, in bits (8, 16, 32 or 64).

Q_ATOMIC_INTnn_TEST_AND_SET_IS_WAIT_FREE

This macro is defined together with Q_ATOMIC_INTnn_TEST_AND_SET_IS_ALWAYS_NATIVE to indicate that the atomic test-and-set on integers is wait-free.

nn is the size of the integer, in bits (8, 16, 32 or 64).

内容

• 公共函数

• 静态公共成员

• 相关非成员

• 宏

• 详细描述

• 原子 API

• 用于原子 API 的特征测试