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
3) Creates new
other
. After this call
other
no longer represents a thread of execution.
std::thread
object and associates it with a thread of execution. The new thread of execution starts executing
/*INVOKE*/(std::move(f_copy), std::move(args_copy)...)
, where
-
/*INVOKE*/
performs theINVOKE
operation specified in Callable, which can be performed bystd::invoke
(since C++17), and -
f_copy
is an object of typestd::decay<Function>::type
and constructed fromstd::forward<Function>(f)
, and -
args_copy...
are objects of typesstd::decay<Args>::type...
and constructed fromstd::forward<Args>(args)...
.
INVOKE
operation is invalid.
This constructor does not participate in overload resolution if
std::decay<Function>::type
is the same type as
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.
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
#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 a copy of object b t2.join(); t4.join(); t5.join(); t6.join(); std::cout << "Final value of n is " << n << '\n'; std::cout << "Final value of f.n (foo::n) is " << f.n << '\n'; std::cout << "Final value of b.n (baz::n) is " << b.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 f.n (foo::n) is 5 Final value of b.n (baz::n) is 0
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 | constructor taking a Callable object might be ambiguous with the move constructor | constrained |
References
- C++20 standard (ISO/IEC 14882:2020):
- 32.4.2.2 thread constructors [thread.thread.constr]
- C++17 standard (ISO/IEC 14882:2017):
- 33.3.2.2 thread constructors [thread.thread.constr]
- C++14 standard (ISO/IEC 14882:2014):
- 30.3.1.2 thread constructors [thread.thread.constr]
- C++11 standard (ISO/IEC 14882:2011):
- 30.3.1.2 thread constructors [thread.thread.constr]
See also
constructs new jthread object (public member function of std::jthread ) |
|
C documentation for thrd_create |
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