Problem with mutex.lock()

[Konstantin Belousov]

On Mon, Feb 11, 2019 at 11:09:29AM +0000, Banta Plan wrote:
> I compiled this program and it crashes if executed.
> 
> Compiled with: FreeBSD clang version 6.0.1 (tags/RELEASE_601/final 335540) (based on LLVM 6.0.1)
> 
> ## CMakeLists.txt
> cmake_minimum_required(VERSION 3.13)
> project(mainP)
> 
> set(CMAKE_CXX_STANDARD 17)
> 
> add_executable(mainP main.cpp)
> 
> find_package(Threads)
> target_link_libraries(mainP ${CMAKE_THREAD_LIBS_INIT})
> 
> ## main.cpp
> 
> #include <iostream>
> #include <thread>
> #include <mutex>
> #include <chrono>
> #include <functional>
> 
> int main() {
>     using namespace std::chrono_literals;
>     std::mutex m;
>     m.lock();
>     std::thread([&] {
>         std::cout << "Before sleepFor" << std::endl;
>         std::this_thread::sleep_for(2s);
> 
>         std::cout << "Before unlock" << std::endl;
>         m.unlock();
This unlock is performed on the mutex that the calling thread does not
hold the lock on.  The behaviour for such case is undefined, from my reading
of C++17 std.

FreeBSD pthread mutexes check this condition.

>         std::cout << "After unlock" << std::endl;
> 
>     }).detach();
>     std::cout << "Before lock2" << std::endl;
>     m.lock();
>     std::cout << "After lock2" << std::endl;
> 
>     return 0;
> }
> ##
> 
> This program compiles and runs under MacOS (Clang Version: Apple LLVM version 10.0.0 (clang-1000.11.45.5)) and
> manjaro arm64 with gcc (GCC) 8.2.1 20180831
> 
> 
> 
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