Difference between revisions of "Template:cpp/atomic/atomic/wait"
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Performs atomic waiting operations. | Performs atomic waiting operations. | ||
| − | 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 | + | 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()}}. |
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| + | These functions are guaranteed to return only if value has changed, even if underlying implementation unblocks spuriously. | ||
===Parameters=== | ===Parameters=== | ||
Revision as of 07:15, 25 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.
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 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)
|
| (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) |
