public member function
<thread>

std::thread::thread

default (1)
thread() noexcept;
initialization (2)
template <class Fn, class... Args>
explicit thread (Fn&& fn, Args&&... args);
copy [deleted] (3)
thread (const thread&) = delete;
move (4)
thread (thread&& x) noexcept;
Construct thread
Constructs a thread object:

(1) default constructor
Construct a thread object that does not represent any thread of execution.
(2) initialization constructor
Construct a thread object that represents a new joinable thread of execution.
The new thread of execution calls fn passing args as arguments (using decay copies of its lvalue or rvalue references).
The completion of this construction synchronizes with the beginning of the invocation of this copy of fn.
(3) copy constructor
Deleted constructor form (thread objects cannot be copied).
(4) move constructor
Construct a thread object that acquires the thread of execution represented by x (if any). This operation does not affect the execution of the moved thread in any way, it simply transfers its handler.
The x object no longer represents any thread of execution.

thread objects that are joinable shall either be joined or detached before they are destroyed.

Parameters

fn
A pointer to function, pointer to member, or any kind of move-constructible function object (i.e., an object whose class defines operator(), including closures and function objects).
The return value (if any) is ignored.
args...
Arguments passed to the call to fn (if any). Their types shall be move-constructible.
If fn is a member pointer, the first argument shall be an object for which that member is defined (or a reference, or a pointer to it).
x
thread object whose state is moved to the constructed object.
Fn and Args... are template parameters: if implicitly deduced, these are the proper lvalue or rvalue reference type to bind the arguments to. Note though, that on the call to fn in the new thread, decay copies of fn and args... are always used (see std::ref for a wrapper class that makes references copyable).

Example

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// constructing threads
#include <iostream>       // std::cout
#include <atomic>         // std::atomic
#include <thread>         // std::thread
#include <vector>         // std::vector

std::atomic<int> global_counter (0);

void increase_global (int n) { for (int i=0; i<n; ++i) ++global_counter; }

void increase_reference (std::atomic<int>& variable, int n) { for (int i=0; i<n; ++i) ++variable; }

struct C : std::atomic<int> {
  C() : std::atomic<int>(0) {}
  void increase_member (int n) { for (int i=0; i<n; ++i) fetch_add(1); }
};

int main ()
{
  std::vector<std::thread> threads;

  std::cout << "increase global counter with 10 threads...\n";
  for (int i=1; i<=10; ++i)
    threads.push_back(std::thread(increase_global,1000));

  std::cout << "increase counter (foo) with 10 threads using reference...\n";
  std::atomic<int> foo;
  for (int i=1; i<=10; ++i)
    threads.push_back(std::thread(increase_reference,std::ref(foo),1000));

  std::cout << "increase counter (bar) with 10 threads using member...\n";
  C bar;
  for (int i=1; i<=10; ++i)
    threads.push_back(std::thread(&C::increase_member,std::ref(bar),1000));

  std::cout << "synchronizing all threads...\n";
  for (auto& th : threads) th.join();

  std::cout << "global_counter: " << global_counter << '\n';
  std::cout << "foo: " << foo << '\n';
  std::cout << "bar: " << bar << '\n';

  return 0;
}


Output:
increase global counter using 10 threads...
increase counter (foo) with 10 threads using reference...
increase counter (bar) with 10 threads using member...
synchronizing all threads...
global_counter: 10000
foo: 10000
bar: 10000

Data races

The move constructor (4) modifies x.

Exception safety

The initialization constructor (2) throws an exception on the following conditions:
exception typeerror conditiondescription
system_errorerrc::resource_unavailable_try_againThe system is unable to start a new thread
It also throws if the construction of any of the copies it makes (of the decay types of Fn and Args...) throws.
Depending on the library implementation, this constructor may also throw exceptions to report other situations (such as bad_alloc or system_error with other error conditions).

Note that if an exception is thrown from the function invocation (i.e., from fn itself), it is handled by the new thread. If this invocation terminates with an uncaught exception, terminate() is called.

See also

<thread>