std::thread::thread - cppreference.com (original) (raw)

thread() noexcept; (1) (since C++11)
thread( thread&& other ) noexcept; (2) (since C++11)
template< class F, class... Args > explicit thread( F&& f, Args&&... args ); (3) (since C++11)
thread( const thread& ) = delete; (4) (since C++11)

Constructs a new std::thread object.

  1. Creates a new std::thread object which does not represent a thread.

  2. Move constructor. Constructs the std::thread object to represent the thread of execution that was represented by other. After this call other no longer represents a thread of execution.

  3. Creates a new std::thread object and associates it with a thread of execution. The new thread of execution starts executing:

The calls of decay-copy are evaluated(until C++23)The values produced by auto are materialized(since C++23) in the current thread, so that any exceptions thrown during evaluation and copying/moving of the arguments are thrown in the current thread, without starting the new thread.

This overload participates in overload resolution only if std::decay<F>::type(until C++20)std::remove_cvref_t<F>(since C++20) is not the same type as std::thread.

The completion of the invocation of the constructor synchronizes with the beginning of the invocation of the copy of f on the new thread of execution.

  1. The copy constructor is deleted; threads are not copyable. No two std::thread objects may represent the same thread of execution.

Contents

[edit] Parameters

other - another thread object to construct this thread object with
f - Callable object to execute in the new thread
args - arguments to pass to the new function

[edit] Postconditions

  1. other.get_id() equal to std::thread::id() and get_id() returns the value of other.get_id() prior to the start of construction.

[edit] Exceptions

  1. std::system_error if the thread could not be started. The exception may represent the error condition std::errc::resource_unavailable_try_again or another implementation-specific error condition.

[edit] Notes

The arguments to the thread function are moved or copied by value. If a reference argument needs to be passed to the thread function, it has to be wrapped (e.g., with std::ref or std::cref).

Any return value from the function is ignored. If the function throws an exception, std::terminate is called. In order to pass return values or exceptions back to the calling thread, std::promise or std::async may be used.

[edit] Example

Possible output:

Thread 1 executing Thread 2 executing Thread 3 executing Thread 4 executing Thread 3 executing Thread 1 executing Thread 2 executing Thread 4 executing Thread 2 executing Thread 3 executing Thread 1 executing Thread 4 executing Thread 3 executing Thread 2 executing Thread 1 executing Thread 4 executing Thread 3 executing Thread 1 executing Thread 2 executing Thread 4 executing Final value of n is 5 Final value of f.n (foo::n) is 5 Final value of b.n (baz::n) is 0

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2097 C++11 for overload (3), F could be std::thread F is constrained
LWG 3476 C++20 overload (3) directly required (the decayed types of)F and the argument types to be move constructible removed theserequirements[1]
  1. ↑ The move-constructibility is already indirectly required by std::is_constructible_v.

[edit] References

[edit] See also