jthread lite: C++20's jthread for C++11 and later

A work in its infancy. Suggested by Peter Featherstone.

Contents

• Example usage
• In a nutshell
• License
• Dependencies
• Installation
• Synopsis
• Other implementations of jthread
• Notes and references
• Appendix

Example usage

#include "nonstd/jthread.hpp"
#include <iostream>

int main(int argc, char **)
{
    int product = 0;
    const int six = 6;
    const int seven = 7;

    {
        nonstd::jthread thr{[&](int x, int y){ product = x * y; }, six, seven };

        // automatically join thread here, making sure it has executed:
    }

    std::cout << "Product of "<< six << " and " << seven << " is " << product << ".\n";
}

Compile and run

$ g++ -std=c++11 -Wall -I../include/ -o 02-arguments.exe 02-arguments.cpp && 02-arguments.exe
Product of 6 and 7 is 42.

In a nutshell

jthread lite is a single-file header-only library to provide C++20's class jthread for use with C++11 and later. If available, the standard library is used, unless configured otherwise.

Currently nonstd::jthread does not (yet) support thread cancellation using stop_token, stop_source and stop_callback. It also does not support std::condition_variable_any.

Features and properties of jthread lite are ease of installation (single header), freedom of dependencies other than the standard library.

Limitations of jthread lite are ... [to be summed up].

License

jthread lite is distributed under the Boost Software License.

Dependencies

jthread lite has no other dependencies than the C++ standard library.

Installation

jthread lite is a single-file header-only library. Put jthread.hpp in the include folder directly into the project source tree or somewhere reachable from your project.

Synopsis

• Documentation of class jthread
• jthread lite implementation status
• Configuration

Documentation of class jthread

[Envisioned] Depending on the compiler and C++ standard used, jthread lite behaves less or more like the standard's version. To get an idea of the capabilities of jthread lite with your configuration, look at the output of the tests, issuing jthread-main.t --pass @.

For the standard's documentation, see class jthread, which is part of the C++ thread library.

jthread lite implementation status

Kind	Type or function	Notes
Type	jthread	present, no stop abilities
	nostopstate_t	present
	stop_token	present, no functionality
	stop_source	present, no functionality
	stop_callback	not present, no functionality
	condition_variable_any	not present, no functionality
Objects	nostopstate	macro for pre-C++17 (no inline var.)
Utilities	make_stop_callback()	not present, deduction guideline workaround

Configuration

Tweak header

If the compiler supports __has_include(), jthread lite supports the tweak header mechanism. Provide your tweak header as nonstd/jthread.tweak.hpp in a folder in the include-search-path. In the tweak header, provide definitions as documented below, like #define jthread_CPLUSPLUS 201103L.

Select std::jthread or nonstd::jthread

[To be implemented]

At default, jthread lite uses std::jthread if it is available and lets you use it via namespace nonstd. You can however override this default and explicitly request to use std::jthread or jthread lite's nonstd::jthread as nonstd::jthread via the following macros.

-Djthread_CONFIG_SELECT_JTHREAD=jthread_SELECT_JTHREAD_NONSTD
Define this to jthread__CONFIG_SELECT_JTHREAD_STD to select std::jthread as nonstd::jthread. Define this to jthread_SELECT_JTHREAD_NONSTD to select nonstd::jthread as nonstd::jthread. Default is undefined, which has the same effect as defining to jthread_SELECT_JTHREAD_NONSTD currently (this may change to jthread_SELECT_JTHREAD_DEFAULT).

Standard selection macro

-Djthread_CPLUSPLUS=199711L
Define this macro to override the auto-detection of the supported C++ standard, if your compiler does not set the __cplusplus macro correctly.

Disable exceptions

-Djthread_CONFIG_NO_EXCEPTIONS=0 Define this to 1 if you want to compile without exceptions. If not defined, the header tries and detect if exceptions have been disabled (e.g. via -fno-exceptions). Default is undefined.

Other implementations of jthread

• jthread. Nicolai Josuttis. GitHub.

Notes and references

• p0660 - Stop Token and Joining Thread. Nicolai Josuttis, Lewis Baker, Billy O’Neal, Herb Sutter, Anthony Williams. 2019.

Appendix

A.1 Compile-time information

The version of jthread lite is available via tag [.version]. The following tags are available for information on the compiler and on the C++ standard library used: [.compiler], [.stdc++], [.stdlanguage] and [.stdlibrary].

A.2 Jthread lite test specification

click to expand

jthread: Allows to default-construct a jthread
jthread: Allows to create a thread with a callback - no parameters
jthread: Allows to create a thread with a callback - with parameters
jthread: Allows to check if a thread is joinable
jthread: Allows to join a thread
jthread: Allows to detach a thread
jthread: Allows to obtain stop_source - stop_source not-implemented
jthread: Allows to obtain stop_token - stop_token not-implemented
jthread: Allows to request a thread to stop - stop_token not-implemented
jthread: Allows to swap two threads
jthread: Allows to obtain a thread's id[.jthread][.info]
jthread: Allows to obtain a thread's native handle[.jthread][.info]
jthread: Allows to obtain the maximum number of hardware threads[.jthread][.info]
tweak header: Reads tweak header if supported [tweak]