Difference between revisions of "Template:cpp/atomic/atomic/wait"
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Revision as of 08:49, 17 December 2019
Template:cpp/atomic//title Template:cpp/atomic//navbar
| (1) | (since C++20) | |
| void wait( old, std::memory_order = std::memory_order::seq_cst ) const noexcept; |
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| void wait( old, std::memory_order = std::memory_order::seq_cst ) const volatile noexcept; |
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Provides a means to check if the object's value is not the old one, and if it is the old one then blocks until its value changes to something else. This form of change-detection is often more efficient than simple polling or pure spinlocks.
while(true) { if (load(order) != old) return; block_until_modified(this); // exposition only - implementation defined }
The correlary functions to unblock are notify_one() or notify_all(), but see Notes section.
Contents |
Preconditions
order is neither std::memory_order::release nor std::memory_order::acq_rel.
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 nor std::memory_order::acq_rel |
Return value
(none)
Notes
Due to the ABA problem, transient changes from old to something else and back to old might be missed, and not unblock.
Because the logical block_until_modified() pseudo-code is implementation defined, the functions may unblock and return due to reasons other than a notifying function being invoked.
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) |
