Default Stack Size

Before diving into customizing the stack size, let’s understand the default behavior. By default, the stack size allocated to a std::jthread is implementation-defined. This means that the stack size may vary depending on the compiler and operating system.

Customizing the Stack Size

The C++ Standard Library provides a function std::thread::native_handle() that returns the underlying thread handle. Once we have the native handle, we can use platform-specific mechanisms to control the stack size.

#include <thread>

#ifdef _WIN32
#include <windows.h>
#elif defined(__linux__)
#include <pthread.h>
#endif

void setStackSize(std::jthread& thread, std::size_t stackSize)
{
    // Get the native handle
    std::thread::native_handle_type handle = thread.native_handle();

#ifdef _WIN32
    // Windows specific code
    SetThreadStackGuarantee(reinterpret_cast<PULONG_PTR>(&handle), stackSize);
#elif defined(__linux__)
    // Linux specific code
    pthread_attr_t attr;
    pthread_attr_init(&attr);
    pthread_attr_setstacksize(&attr, stackSize);
    pthread_attr_setinheritsched(&attr, PTHREAD_EXPLICIT_SCHED);
    pthread_attr_setschedpolicy(&attr, SCHED_FIFO);
    pthread_attr_setschedparam(&attr, { 1 }); // Set priority to 1 (lowest)
    pthread_create(&handle, &attr, nullptr, nullptr);
#else
    // Your custom implementation for other platforms
    #error Stack size customization is not supported on this platform
#endif
}

In this code snippet, we define a function setStackSize that takes a std::jthread and a desired stack size. We obtain the native handle using native_handle(). Next, we use conditional compilation to differentiate between Windows and Linux platforms.

For Windows, we use the SetThreadStackGuarantee function to set the stack size. On Linux, we use the pthread_attr_setstacksize function to customize the stack size. We also set the scheduling policy using other functions like pthread_attr_setinheritsched and pthread_attr_setschedparam.

Remember to set an appropriate stack size based on your requirements. The stack size is typically specified in bytes.

Conclusion

In this blog post, we learned how to control the stack size of a std::jthread using C++ Standard Library features. By customizing the stack size, we can optimize the memory usage of our threads and handle scenarios where the default stack size is not sufficient. Remember to use platform-specific mechanisms to set the stack size, as demonstrated in the code snippet above.

#cpp #C++ #stdjthread #stacksize