Difference between revisions of "cpp/atomic/atomic flag test and set"
From cppreference.com
m (Text replace - "===Equivalent definition===" to "===Possible implementation===") |
m (Text replace - "{{example cpp" to "{{example") |
||
| Line 61: | Line 61: | ||
===Example=== | ===Example=== | ||
| − | {{example | + | {{example |
| A spinlock mutex can be implemented in userspace using an atomic_flag | | A spinlock mutex can be implemented in userspace using an atomic_flag | ||
| code= | | code= | ||
Revision as of 15:41, 19 April 2012
Template:cpp/atomic/sidebar Template:ddcl list begin <tr class="t-dsc-header">
<td>Defined in header
</td>
<atomic>
<td></td> <td></td> </tr> <tr class="t-dcl ">
<td >bool atomic_flag_test_and_set( volatile std::atomic_flag* p );
</td>
<td > (1) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">
<td >bool atomic_flag_test_and_set( std::atomic_flag* p );
</td>
<td > (2) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">
<td >bool atomic_flag_test_and_set_explicit( volatile std::atomic_flag* p,
std::memory_order order );
</td>
std::memory_order order );
<td > (3) </td> <td > (since C++11) </td> </tr> <tr class="t-dcl ">
<td >bool atomic_flag_test_and_set_explicit( std::atomic_flag* p,
std::memory_order order );
</td>
std::memory_order order );
<td > (4) </td> <td > (since C++11) </td> </tr> Template:ddcl list end
Atomically changes the state of a Template:cpp pointed to by p to set (Template:cpp) and returns the value it held before.
Contents |
Parameters
| p | - | pointer to Template:cpp to access |
| order | - | the memory sycnhronization ordering for this operation |
Return value
The value previously held by the flag pointed to by p
Exceptions
noexcept specification:
noexcept
Possible implementation
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(std::atomic_flag_test_and_set_explicit(&lock, std::memory_order_acquire)) ; // spin until the lock is acquired std::cout << "Output from thread " << n << '\n'; std::atomic_flag_clear_explicit(&lock, std::memory_order_release); } } 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>...
