Difference between revisions of "Template:cpp/atomic/atomic/wait"
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Compares the [[cpp/language/object|value representation]] of the {{c|this->{{#ifeq:{{{1|}}}|atomic_flag|test|load}}(order)}} with that of {{tt|old}}, and if those are bitwise equal then blocks until the one of {{c|this->{{#ifeq:{{{1|}}}|atomic_flag|test|load}}(order)}} changes or {{c|*this}} is notified by {{lc|notify_one()}} or {{lc|notify_all()}}. These functions are allowed to unblock spuriously, i.e. return due to reasons other than value change or notification. | Compares the [[cpp/language/object|value representation]] of the {{c|this->{{#ifeq:{{{1|}}}|atomic_flag|test|load}}(order)}} with that of {{tt|old}}, and if those are bitwise equal then blocks until the one of {{c|this->{{#ifeq:{{{1|}}}|atomic_flag|test|load}}(order)}} changes or {{c|*this}} is notified by {{lc|notify_one()}} or {{lc|notify_all()}}. These functions are allowed to unblock spuriously, i.e. return due to reasons other than value change or notification. | ||
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===Parameters=== | ===Parameters=== | ||
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===Notes=== | ===Notes=== | ||
| + | This form of change-detection is often more efficient than simple polling or pure spinlocks. | ||
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Due to the [https://en.wikipedia.org/wiki/ABA_problem ABA problem], transient changes from {{tt|old}} to something else and back to {{tt|old}} might be missed, and not unblock. | Due to the [https://en.wikipedia.org/wiki/ABA_problem ABA problem], transient changes from {{tt|old}} to something else and back to {{tt|old}} might be missed, and not unblock. | ||
Revision as of 06:59, 8 February 2020
Template:cpp/atomic//title Template:cpp/atomic//navbar
| (since C++20) | ||
| void wait( T old, std::memory_order = std::memory_order::seq_cst ) const noexcept; |
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| void wait( T old, std::memory_order = std::memory_order::seq_cst ) const volatile noexcept; |
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Compares the value representation of the this->load(order) with that of old, and if those are bitwise equal then blocks until the one of this->load(order) changes or *this is notified by notify_one() or notify_all(). These functions are allowed to unblock spuriously, i.e. return due to reasons other than value change or notification.
Contents |
Parameters
| old | - | the value to check the 's object no longer contains |
| order | - | the memory synchronization ordering for this operation: must not be std::memory_order::release or std::memory_order::acq_rel |
Return value
(none)
Notes
This form of change-detection is often more efficient than simple polling or pure spinlocks.
Due to the ABA problem, transient changes from old to something else and back to old might be missed, and not unblock.
Example
| This section is incomplete |
See also
| (C++20) |
notifies at least one thread waiting on the atomic object (public member function of Template:cpp/atomic//title)
|
| (C++20) |
notifies all threads blocked waiting on the atomic object (public member function of Template:cpp/atomic//title)
|
| (C++20) |
notifies a thread blocked in atomic_wait (function template) |
| (C++20) |
notifies all threads blocked in atomic_wait (function template) |
