Defined in header <stop_token> | ||
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class stop_source; | (since C++20) |
The stop_source class provides the means to issue a stop request, such as for std::jthread cancellation. A stop request made for one stop_source object is visible to all stop_sources and std::stop_tokens of the same associated stop-state; any std::stop_callback(s) registered for associated std::stop_token(s) will be invoked, and any std::condition_variable_any objects waiting on associated std::stop_token(s) will be awoken.
Once a stop is requested, it cannot be withdrawn. Additional stop requests have no effect.
| constructs new stop_source object (public member function) |
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| destructs the stop_source object (public member function) |
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| assigns the stop_source object (public member function) |
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Modifiers |
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| makes a stop request for the associated stop-state, if any (public member function) |
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| swaps two stop_source objects (public member function) |
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Observers |
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returns a stop_token for the associated stop-state (public member function) |
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| checks whether the associated stop-state has been requested to stop (public member function) |
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| checks whether associated stop-state can be requested to stop (public member function) |
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compares two std::stop_source objects (function) |
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(C++20) | specializes the std::swap algorithm (function) |
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(C++20) | a std::nostopstate_t instance for use in stop_source constructor (constant) |
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(C++20) | placeholder type for use in stop_source constructor (class) |
For the purposes of std::jthread cancellation the stop_source object should be retrieved from the std::jthread object using get_stop_source(); or stop should be requested directly from the std::jthread object using request_stop(). This will then use the same associated stop-state as that passed into the std::jthread's invoked function argument (i.e., the function being executed on its thread).
For other uses, however, a stop_source can be constructed separately using the default constructor, which creates new stop-state.
| Feature-test macro | Value | Std | Comment |
|---|---|---|---|
__cpp_lib_jthread | 201911L | (C++20) | Stop token and joining thread |
#include <chrono>
#include <iostream>
#include <stop_token>
#include <thread>
using namespace std::chrono_literals;
void worker_fun(int id, std::stop_source stop_source)
{
std::stop_token stoken = stop_source.get_token();
for (int i = 10; i; --i) {
std::this_thread::sleep_for(300ms);
if (stoken.stop_requested())
{
std::printf(" worker%d is requested to stop\n", id);
return;
}
std::printf(" worker%d goes back to sleep\n", id);
}
}
int main()
{
std::jthread threads[4];
std::cout << std::boolalpha;
auto print = [](const std::stop_source &source)
{
std::printf("stop_source stop_possible = %s, stop_requested = %s\n",
source.stop_possible() ? "true" : "false",
source.stop_requested() ? "true" : "false");
};
// Common source
std::stop_source stop_source;
print(stop_source);
// Create worker threads
for (int i = 0; i < 4; ++i)
threads[i] = std::jthread(worker_fun, i + 1, stop_source);
std::this_thread::sleep_for(500ms);
std::puts("Request stop");
stop_source.request_stop();
print(stop_source);
// Note: destructor of jthreads will call join so no need for explicit calls
}Possible output:
stop_source stop_possible = true, stop_requested = false worker2 goes back to sleep worker3 goes back to sleep worker1 goes back to sleep worker4 goes back to sleep Request stop stop_source stop_possible = true, stop_requested = true worker3 is requested to stop worker1 is requested to stop worker2 is requested to stop worker4 is requested to stop
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