Difference between revisions of "cpp/atomic/atomic flag"
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| − | + | {{c|std::atomic_flag}} is an atomic boolean type. Unlike all specializations of {{c|std::atomic}}, it is guaranteed to be lock-free. Unlike {{c|std::atomic<bool>}}, {{tt|std::atomic_flag}} does not provide load or store operations. | |
===Member functions=== | ===Member functions=== | ||
Revision as of 10:11, 28 August 2012
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<td>Defined in header
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<atomic>
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<td >class atomic_flag;
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<td class="t-dcl-nopad"> </td> <td > (since C++11) </td> </tr> Template:ddcl list end
std::atomic_flag is an atomic boolean type. Unlike all specializations of std::atomic, it is guaranteed to be lock-free. Unlike std::atomic<bool>, std::atomic_flag does not provide load or store operations.
Member functions
| constructs an atomic_flag (public member function) | |
| the assignment operator (public member function) |
Example
A spinlock mutex can be implemented in userspace using an atomic_flag
Run this code
#include <thread> #include <vector> #include <iostream> #include <atomic> std::atomic_flag lock = ATOMIC_FLAG_INIT; void f(int n) { for(int cnt = 0; cnt < 100; ++cnt) { while(lock.test_and_set(std::memory_order_acquire)) // acquire lock ; // spin std::cout << "Output from thread " << n << '\n'; lock.clear(std::memory_order_release); // release lock } } int main() { std::vector<std::thread> v; for (int n = 0; n < 10; ++n) { v.emplace_back(f, n); } for (auto& t : v) { t.join(); } }
Output:
Output from thread 2 Output from thread 6 Output from thread 7 ...<exactly 1000 lines>...
See also
| C documentation for atomic_flag
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