Create a thread
123456789101112131415161718 | #include <thread>
#include <string>
#include <functional>
void func(std::string str, int& x);
void do_something();
int main()
{
std::string str = "Test";
int x = 5;
std::thread t{func, str, std::ref(x)};
do_something();
t.join();
} |
This pattern is licensed under the CC0 Public Domain Dedication.
Intent
Execute code on a separate thread.
Description
On line 13, we create a std::thread object t,
which represents a thread of execution. When constructing t, we
pass func as the function to execute on that thread.
To pass arguments to func, we have passed them as additional
arguments to std::thread’s constructor. Notice that to pass an
argument by reference, it must be wrapped in a
std::reference_wrapper
— to do this, we use the std::ref
helper function. For const references, use
std::cref.
After creating the thread, the remainder of main continues to
execute as normal. At the same time, function func begins
executing in the newly-created thread. This means that the bodies
of func and main will be executing concurrently. They may be
executed in parallel if the system supports parallel execution.
On line 17 we call t’s join member
function. This causes main’s thread to block until the thread
finishes execution (which is when func returns). Once join
returns, execution continues in main’s thread.
Note: A thread must be either joined or detached before
destruction, or std::terminate will be
called.
Note: If func propagates an exception, std::terminate will
be called.
