std::thread::thread
thread() noexcept; |
(1) | (since C++11) |
thread( thread&& other ) noexcept; |
(2) | (since C++11) |
template< class Function, class... Args > explicit thread( Function&& f, Args&&... args ); |
(3) | (since C++11) |
thread(const thread&) = delete; |
(4) | (since C++11) |
Constructs new thread object.
1) Creates new thread object which does not represent a thread.
2) Move constructor. Constructs the 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no longer represents a thread of execution.3) Creates new
Except that the calls to
std::thread
object and associates it with a thread of execution. The new thread of execution starts executing std::invoke(decay_copy(std::forward<Function>(f)), decay_copy(std::forward<Args>(args))...);
where decay_copy
is defined as
template <class T> std::decay_t<T> decay_copy(T&& v) { return std::forward<T>(v); }
decay_copy
are evaluated in the context of the caller, so that any exceptions thrown during evaluation and copying/moving of the arguments are thrown in the current thread, without starting the new thread. The completion of the invocation of the constructor synchronizes-with (as defined in std::memory_order) the beginning of the invocation of the copy of f on the new thread of execution.
This constructor does not participate in overload resolution if std::decay_t<Function> is the same type as std::thread.
|
(since C++14) |
4) The copy constructor is deleted; threads are not copyable. No two
std::thread
objects may represent the same thread of execution.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 |
Postconditions
2) other.get_id() equal to std::thread::id() and get_id() returns the value of other.get_id() prior to the start of construction
Exceptions
3) 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.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.
Example
Run this code
#include <iostream> #include <utility> #include <thread> #include <chrono> void f1(int n) { for (int i = 0; i < 5; ++i) { std::cout << "Thread 1 executing\n"; ++n; std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } void f2(int& n) { for (int i = 0; i < 5; ++i) { std::cout << "Thread 2 executing\n"; ++n; std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } class foo { public: void bar() { for (int i = 0; i < 5; ++i) { std::cout << "Thread 3 executing\n"; ++n; std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } int n = 0; }; class baz { public: void operator()() { for (int i = 0; i < 5; ++i) { std::cout << "Thread 4 executing\n"; ++n; std::this_thread::sleep_for(std::chrono::milliseconds(10)); } } int n = 0; }; int main() { int n = 0; foo f; baz b; std::thread t1; // t1 is not a thread std::thread t2(f1, n + 1); // pass by value std::thread t3(f2, std::ref(n)); // pass by reference std::thread t4(std::move(t3)); // t4 is now running f2(). t3 is no longer a thread std::thread t5(&foo::bar, &f); // t5 runs foo::bar() on object f std::thread t6(b); // t6 runs baz::operator() on object b t2.join(); t4.join(); t5.join(); t6.join(); std::cout << "Final value of n is " << n << '\n'; std::cout << "Final value of foo::n is " << f.n << '\n'; }
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 foo::n is 5
References
- C++11 standard (ISO/IEC 14882:2011):
- 30.3.1.2 thread constructors [thread.thread.constr]