How do I use the pthreads in a ROS C++ Node - c++

Question

I am trying to use pthread library inside the ros Node, I am including it as #include <pthread>. When I run catkin_make I get the error below. I created a simple thread as std::thread m1(move, 1);
thread: No such file or directory
#include <pthread>
^~~~~~~~~
The signature of the move function is void move(short axis_no, short direction = 0) and I instantiated the thread as
std::thread m1(move, 1);
m1.join();
I tried to add the pthread library in my CmakeLists.txt as follows
add_compile_options(-std=c++11 -pthread) and
target_link_libraries(pthread). Is there a way I can use the pthread library inside the ros Node?
Thank you.

Answer 1

pthread is a C library available on some platforms and if you want to use the pthread_* functions you need to #include <pthread.h>.
Since C++11 there is an abstraction layer on top of the native threading libraries which is available if you instead #include <thread>.
You can then use std::thread - but you will still need to link with -pthread.
Instead of hardcoding -pthread, you can let CMake find and add the appropriate library:
find_package(Threads REQUIRED)
target_link_libraries(your_app PRIVATE Threads::Threads)
In your program, the move function needs two arguments (the function signature is void(*)(short, short) even if you have a default value for direction).
#include <thread>
#include <iostream>
void move(short axis_no, short direction = 0) {
std::cout << axis_no << ' ' << direction << '\n';
}
int main() {
auto th = std::thread(move, 1, 2); // needs 2 arguments
th.join();
}
If you want, you can create an overload to only have to supply one argument, but in that case you also need to help the compiler to select the correct overload.
#include <thread>
#include <iostream>
void move(short axis_no, short direction) { // no default value here
std::cout << axis_no << ' ' << direction << '\n';
}
void move(short axis_no) { // proxy function
move(axis_no, 0); // where 0 is default
}
int main() {
using one = void(*)(short);
using two = void(*)(short, short);
// use one of the above type aliases to select the proper overload:
auto th = std::thread(static_cast<one>(move), 1);
th.join();
}