https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92546
--- Comment #12 from CVS Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jonathan Wakely <r...@gcc.gnu.org>: https://gcc.gnu.org/g:b204d7722d30f44281dea3341070223475f1cff9 commit r11-5168-gb204d7722d30f44281dea3341070223475f1cff9 Author: Jonathan Wakely <jwak...@redhat.com> Date: Thu Nov 19 13:36:15 2020 +0000 libstdc++: Move std::thread to a new header This makes it possible to use std::thread without including the whole of <thread>. It also makes this_thread::get_id() and this_thread::yield() available even when there is no gthreads support (e.g. when GCC is built with --disable-threads or --enable-threads=single). In order for the std::thread::id return type of this_thread::get_id() to be defined, std:thread itself is defined unconditionally. However the constructor that creates new threads is not defined for single-threaded builds. The thread::join() and thread::detach() member functions are defined inline for single-threaded builds and just throw an exception (because we know the thread cannot be joinable if the constructor that creates joinable threads doesn't exit). The thread::hardware_concurrency() member function is also defined inline and returns 0 (as suggested by the standard when the value "is not computable or well-defined"). The main benefit for most targets is that other headers such as <future> do not need to include the whole of <thread> just to be able to create a std::thread. That avoids including <stop_token> and std::jthread where not required. This is another partial fix for PR 92546. This also means we can use this_thread::get_id() and this_thread::yield() in <stop_token> instead of using the gthread functions directly. This removes some preprocessor conditionals, simplifying the code. libstdc++-v3/ChangeLog: PR libstdc++/92546 * include/Makefile.am: Add new <bits/std_thread.h> header. * include/Makefile.in: Regenerate. * include/std/future: Include new header instead of <thread>. * include/std/stop_token: Include new header instead of <bits/gthr.h>. (stop_token::_S_yield()): Use this_thread::yield(). (_Stop_state_t::_M_requester): Change type to std::thread::id. (_Stop_state_t::_M_request_stop()): Use this_thread::get_id(). (_Stop_state_t::_M_remove_callback(_Stop_cb*)): Likewise. Use __is_single_threaded() to decide whether to synchronize. * include/std/thread (thread, operator==, this_thread::get_id) (this_thread::yield): Move to new header. (operator<=>, operator!=, operator<, operator<=, operator>) (operator>=, hash<thread::id>, operator<<): Define even when gthreads not available. * src/c++11/thread.cc: Include <memory>. * include/bits/std_thread.h: New file. (thread, operator==, this_thread::get_id, this_thread::yield): Define even when gthreads not available. [!_GLIBCXX_HAS_GTHREADS] (thread::join, thread::detach) (thread::hardware_concurrency): Define inline.
