std::atomic_fetch_and, std::atomic_fetch_and_explicit
Min standard notice:
Header: <atomic>
Atomically replaces the value pointed by obj with the result of bitwise AND between the old value of obj and arg. Returns the value obj held previously.
# Declarations
template< class T >
T atomic_fetch_and( std::atomic<T>* obj,
typename std::atomic<T>::value_type arg ) noexcept;
(since C++11)
template< class T >
T atomic_fetch_and( volatile std::atomic<T>* obj,
typename std::atomic<T>::value_type arg ) noexcept;
(since C++11)
template< class T >
T atomic_fetch_and_explicit( std::atomic<T>* obj,
typename std::atomic<T>::value_type arg,
std::memory_order order ) noexcept;
(since C++11)
template< class T >
T atomic_fetch_and_explicit( volatile std::atomic<T>* obj,
typename std::atomic<T>::value_type arg,
std::memory_order order ) noexcept;
(since C++11)
# Parameters
obj: pointer to the atomic object to modifyarg: the value to bitwise AND to the value stored in the atomic objectorder: the memory synchronization ordering
# Return value
The value immediately preceding the effects of this function in the modification order of *obj.
# Example
#include <atomic>
#include <chrono>
#include <functional>
#include <iostream>
#include <thread>
// Binary semaphore for demonstrative purposes only.
// This is a simple yet meaningful example: atomic operations
// are unnecessary without threads.
class Semaphore
{
std::atomic_char m_signaled;
public:
Semaphore(bool initial = false)
{
m_signaled = initial;
}
// Block until semaphore is signaled
void take()
{
while (!std::atomic_fetch_and(&m_signaled, false))
{
std::this_thread::sleep_for(std::chrono::milliseconds(10));
}
}
void put()
{
std::atomic_fetch_or(&m_signaled, true);
}
};
class ThreadedCounter
{
static const int N = 100;
static const int REPORT_INTERVAL = 10;
int m_count;
bool m_done;
Semaphore m_count_sem;
Semaphore m_print_sem;
void count_up()
{
for (m_count = 1; m_count <= N; ++m_count)
if (m_count % REPORT_INTERVAL == 0)
{
if (m_count == N)
m_done = true;
m_print_sem.put(); // signal printing to occur
m_count_sem.take(); // wait until printing is complete proceeding
}
std::cout << "count_up() done\n";
m_done = true;
m_print_sem.put();
}
void print_count()
{
do
{
m_print_sem.take();
std::cout << m_count << '\n';
m_count_sem.put();
}
while (!m_done);
std::cout << "print_count() done\n";
}
public:
ThreadedCounter() : m_done(false) {}
void run()
{
auto print_thread = std::thread(&ThreadedCounter::print_count, this);
auto count_thread = std::thread(&ThreadedCounter::count_up, this);
print_thread.join();
count_thread.join();
}
};
int main()
{
ThreadedCounter m_counter;
m_counter.run();
}
# Defect reports
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| P0558R1 | C++11 | exact type match was required becauseT was deduced from multiple arguments | T is only deducedfrom obj |