Difference between revisions of "Template:cpp/atomic/atomic/wait"
From cppreference.com
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m (atomic_flag) |
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Performs atomic waiting operations. Behaves as if it repeatedly performs the following steps: | Performs atomic waiting operations. Behaves as if it repeatedly performs the following steps: | ||
| − | * Compare the [[cpp/language/object|value representation]] of {{c|this-> | + | * Compare {{#ifeq:{{{1|}}}|atomic_flag||the [[cpp/language/object|value representation]] of {{c|this->test(order)}}|{{c|this->load(order)}}}} with that of {{tt|old}}. |
| − | ** If those are | + | ** If those are equal, then blocks until {{c|*this}} is notified by {{lc|notify_one()}} or {{lc|notify_all()}}, or the thread is unblocked spuriously. |
** Otherwise, returns. | ** Otherwise, returns. | ||
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Due to the [https://en.wikipedia.org/wiki/ABA_problem ABA problem], transient changes from {{tt|old}} to another value 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 another value and back to {{tt|old}} might be missed, and not unblock. | ||
| − | The comparison is bitwise (similar to {{lc|std::memcpy}}); no comparison operator is used. Padding bits that never participate in an object's value representation are ignored. | + | {{#ifeq:{{{1|}}}|atomic_flag||The comparison is bitwise (similar to {{lc|std::memcpy}}); no comparison operator is used. Padding bits that never participate in an object's value representation are ignored.}} |
===Example=== | ===Example=== | ||
Revision as of 02:48, 27 February 2020
Template:cpp/atomic//title Template:cpp/atomic//navbar
| (since C++20) | ||
| void wait( T old, std::memory_order order = std::memory_order::seq_cst ) const noexcept; |
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| void wait( T old, std::memory_order order = std::memory_order::seq_cst ) const volatile noexcept; |
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Performs atomic waiting operations. Behaves as if it repeatedly performs the following steps:
- Compare the value representation of this->test(order) with that of
old.- If those are equal, then blocks until *this is notified by notify_one() or notify_all(), or the thread is unblocked spuriously.
- Otherwise, returns.
These functions are guaranteed to return only if value has changed, even if underlying implementation unblocks spuriously.
Contents |
Parameters
| old | - | the value to check the |
| 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 another value and back to old might be missed, and not unblock.
The comparison is bitwise (similar to std::memcpy); no comparison operator is used. Padding bits that never participate in an object's value representation are ignored.
Example
| This section is incomplete Reason: no example |
See also
| (C++20) |
notifies at least one thread waiting on the atomic object (public member function of Template:cpp/atomic//title)
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| (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) |
