set thread name

[vinniefalco]

Would be nice to have a thread name setting facility for things like io_context or thread_pool threads to know what is what in the debugger. The difficulty is trying to roll this up into something automatic for user-defined threads.

Thread naming isn't standardized in C++, so you need platform-specific code. Here's the portable approach:

Windows (10 1607+):

#include <windows.h>
SetThreadDescription(GetCurrentThread(), L"MyThread");

Linux/FreeBSD:

#include <pthread.h>
pthread_setname_np(pthread_self(), "MyThread");  // max 16 chars including null

macOS:

#include <pthread.h>
pthread_setname_np("MyThread");  // note: no thread handle parameter

Portable wrapper:

#include <string_view>

inline void set_thread_name(std::string_view name)
{
#if defined(_WIN32)
    // Windows 10 1607+ only
    std::wstring wname(name.begin(), name.end());
    SetThreadDescription(GetCurrentThread(), wname.c_str());
#elif defined(__APPLE__)
    pthread_setname_np(std::string(name.substr(0, 63)).c_str());
#elif defined(__linux__) || defined(__FreeBSD__)
    // Linux has 16-char limit including null terminator
    char buf[16];
    auto len = std::min(name.size(), size_t{15});
    std::copy_n(name.data(), len, buf);
    buf[len] = '\0';
    pthread_setname_np(pthread_self(), buf);
#endif
}

Notes:

• Linux has a strict 15-character limit (16 with null terminator)
• Windows SetThreadDescription requires linking against kernel32.lib and only works on Windows 10 1607+
• For older Windows, there's an SEH exception trick (RaiseException with 0x406D1388) but it only works with a debugger attached
• Boost.Thread doesn't provide this either
• Some libraries like fmt or spdlog have their own implementations you could reference

Would you like me to search your codebase for any existing thread naming utilities?

[MungoG]

Windows 8 is out of support, and people debugging tend to use newer versions, so I don't think we need to worry about pre-windows-10 code (maybe just use a macro to ensure the function is a no-op on older windows systems).