How Can I Efficiently Check the Running Status of a std::thread in C ?

Checking the Running Status of a std::thread

In developing multithreaded applications with C , it often becomes necessary to determine the running status of a given std::thread. However, std::thread lacks a convenient timed_join() method, and joinable() is specifically not intended for this purpose.

The C 11 Solution

If you're working with C 11, an elegant solution is to employ std::async and std::future. The wait_for function of std::future enables you to check the thread status in a concise manner:

#include <future>
#include <thread>

auto future = std::async(std::launch::async, [] { ... }); // Run task on a new thread

// Check thread status with zero milliseconds wait time
auto status = future.wait_for(0ms);

if (status == std::future_status::ready)
    // Thread finished
else
    // Thread still running

Using std::promise

For std::thread, you can leverage std::promise to obtain a future object:

#include <future>
#include <thread>

std::promise<bool> p;
auto future = p.get_future();

std::thread t([&amp;p] { ...; p.set_value(true); }); // Run task on a new thread

// Get thread status using wait_for
auto status = future.wait_for(0ms);

Atomic Flag Approach

Another straightforward option is to use an atomic flag:

#include <thread>
#include <atomic>

std::atomic<bool> done(false);

std::thread t([&amp;done] { ...; done = true; }); // Run task with flag setting

if (done)
    // Thread finished
else
    // Thread still running

Std::packaged_task

For a cleaner solution, consider std::packaged_task:

#include <future>
#include <thread>

std::packaged_task<void()> task([] { ... });
auto future = task.get_future();

std::thread t(std::move(task)); // Run task on new thread

// Check thread status using wait_for
auto status = future.wait_for(0ms);

By utilizing these approaches, you can effectively check if a std::thread is still running, ensuring better control and coordination in your multithreaded applications.

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