Share Flags and Values with std::atomic
Learn to share flags and values with std::atomic.
The std::atomic
class encapsulates a single object and guarantees it to be atomic. Writing to the atomic object is controlled by memory-order policies and reads may occur simultaneously. It's typically used to synchronize access among different threads.
std::atomic
defines an atomic type from its template type. The type must be trivial. A type is std::atomic
is most often used with simple primitive types, such as bool
, int
, long
, float
, and double
.
How to do it
This recipe uses a simple function that loops over a counter to demonstrate sharing atomic objects. We will spawn a swarm of these loops as threads that share atomic values:
Atomic objects are often placed in a global namespace. They must be accessible to all the threads that need to share its value:
std::atomic<bool> ready{};std::atomic<uint64_t> g_count{};std::atomic_flag winner{};
The ready
object is a bool
type that gets set to true
when all the threads are ready to start counting. The g_count
object is a global counter. It is incremented by each of the threads. The winner object is a special atomic_flag
type. It is used to indicate which thread finishes first.
We use a couple of constants to control the number of threads and the number of loops for each thread:
constexpr int max_count{1000 * 1000};constexpr int max_threads{100};
Here, we've set it to run
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