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Scoped Threads

Motivation
Tutorial
Free Thread Functors
Class strict_scoped_thread
Class scoped_thread
Non-member function swap(scoped_thread&,scoped_thread&)

Synopsis

//#include <boost/thread/scoped_thread.hpp>

struct detach;
struct join_if_joinable;
struct interrupt_and_join_if_joinable;
template <class CallableThread = join_if_joinable>
class strict_scoped_thread;
template <class CallableThread = join_if_joinable>
class scoped_thread;
void swap(scoped_thread& lhs,scoped_thread& rhs) noexcept;

Based on the scoped_thread class defined in C++ Concurrency in Action Boost.Thread defines a thread wrapper class that instead of calling terminate if the thread is joinable on destruction, call a specific action given as template parameter.

While the scoped_thread class defined in C++ Concurrency in Action is closer to strict_scoped_thread class that doesn't allows any change in the wrapped thread, Boost.Thread provides a class scoped_thread that provides the same non-deprecated interface than thread.

Scoped Threads are wrappers around a thread that allows the user to state what to do at destruction time. One of the common uses is to join the thread at destruction time so this is the default behavior. This is the single difference respect to a thread. While thread call std::terminate() on the destructor is the thread is joinable, strict_scoped_thread<> or scoped_thread<> join the thread if joinable.

The difference between strict_scoped_thread and scoped_thread is that the strict_scoped_thread hides completely the owned thread and so the user can do nothing with the owned thread other than the specific action given as parameter, while scoped_thread provide the same interface than thread and forwards all the operations.

boost::strict_scoped_thread<> t1((boost::thread(F)));
boost::strict_scoped_thread<> t2((boost::thread(F)));
t2.interrupt();
//#include <boost/thread/scoped_thread.hpp>

struct detach;
struct join_if_joinable;
struct interrupt_and_join_if_joinable;
struct detach
{
  void operator()(thread& t)
  {
    t.detach();
  }
};
struct join_if_joinable
{
  void operator()(thread& t)
  {
    if (t.joinable())
    {
      t.join();
    }
  }
};
struct interrupt_and_join_if_joinable
{
  void operator()(thread& t)
  {
    t.interrupt();
    if (t.joinable())
    {
      t.join();
    }
  }
};
// #include <boost/thread/scoped_thread.hpp>

template <class CallableThread = join_if_joinable>
class strict_scoped_thread
{
  thread t_; // for exposition purposes only
public:

  strict_scoped_thread(strict_scoped_thread const&) = delete;
  strict_scoped_thread& operator=(strict_scoped_thread const&) = delete;

  explicit strict_scoped_thread(thread&& t) noexcept;

  ~strict_scoped_thread();

};

RAI thread wrapper adding a specific destroyer allowing to master what can be done at destruction time.

CallableThread: A callable void(thread&).

The default is a join_if_joinable.

std/boost::thread destructor terminates the program if the thread is not joinable. This wrapper can be used to join the thread before destroying it seems a natural need.

Example
boost::strict_scoped_thread<> t((boost::thread(F)));
explicit strict_scoped_thread(thread&& t) noexcept;

Effects:

move the thread to own t_

Throws:

Nothing

~strict_scoped_thread();

Effects:

Equivalent to CallableThread()(t_).

Throws:

Nothing: The CallableThread()(t_) should not throw when joining the thread as the scoped variable is on a scope outside the thread function.

#include <boost/thread/scoped_thread.hpp>

class scoped_thread
{
  thread t_; // for exposition purposes only
public:
    scoped_thread() noexcept;
    scoped_thread(const scoped_thread&) = delete;
    scoped_thread& operator=(const scoped_thread&) = delete;

    explicit scoped_thread(thread&& th) noexcept;

    ~scoped_thread();

    // move support
    scoped_thread(scoped_thread && x) noexcept;
    scoped_thread& operator=(scoped_thread && x) noexcept;

    void swap(scoped_thread& x) noexcept;

    typedef thread::id id;

    id get_id() const noexcept;

    bool joinable() const noexcept;
    void join();
#ifdef BOOST_THREAD_USES_CHRONO
    template <class Rep, class Period>
    bool try_join_for(const chrono::duration<Rep, Period>& rel_time);
    template <class Clock, class Duration>
    bool try_join_until(const chrono::time_point<Clock, Duration>& t);
#endif

    void detach();

    static unsigned hardware_concurrency() noexcept;

    typedef thread::native_handle_type native_handle_type;
    native_handle_type native_handle();

#if defined BOOST_THREAD_PROVIDES_INTERRUPTIONS
    void interrupt();
    bool interruption_requested() const noexcept;
#endif


};

void swap(scoped_thread& lhs,scoped_thread& rhs) noexcept;

RAI thread wrapper adding a specific destroyer allowing to master what can be done at destruction time.

CallableThread: A callable void(thread&). The default is join_if_joinable.

thread std::thread destructor terminates the program if the thread is not joinable. Having a wrapper that can join the thread before destroying it seems a natural need.

Remark: scoped_thread is not a thread as thread is not designed to be derived from as a polymorphic type.

Anyway scoped_thread can be used in most of the contexts a thread could be used as it has the same non-deprecated interface with the exception of the construction.

Example
boost::scoped_thread<> t((boost::thread(F)));
t.interrupt();
scoped_thread() noexcept;

Effects:

Constructs a scoped_thread instance that wraps to Not-a-Thread.

Postconditions:

this->get_id()==thread::id()

Throws:

Nothing

scoped_thread(scoped_thread&& other) noexcept;

Effects:

Transfers ownership of the scoped_thread managed by other (if any) to the newly constructed scoped_thread instance.

Postconditions:

other.get_id()==thread::id() and get_id() returns the value of other.get_id() prior to the construction

Throws:

Nothing

scoped_thread& operator=(scoped_thread&& other) noexcept;

Effects:

Transfers ownership of the scoped_thread managed by other (if any) to *this.

- if defined BOOST_THREAD_DONT_PROVIDE_THREAD_MOVE_ASSIGN_CALLS_TERMINATE_IF_JOINABLE: If there was a scoped_thread previously associated with *this then that scoped_thread is detached, DEPRECATED

- if defined BOOST_THREAD_PROVIDES_THREAD_MOVE_ASSIGN_CALLS_TERMINATE_IF_JOINABLE: If the scoped_thread is joinable calls to std::terminate.

Postconditions:

other->get_id()==thread::id() and get_id() returns the value of other.get_id() prior to the assignment.

Throws:

Nothing

scoped_thread(thread&& t);

Effects:

move the thread to own t_.

Postconditions:

*this.t_ refers to the newly created thread of execution and this->get_id()!=thread::id().

Throws:

Nothing

~scoped_thread();

Effects:

Equivalent to CallableThread()(t_).

Throws:

Nothing: The CallableThread()(t_) should not throw when joining the thread as the scoped variable is on a scope outside the thread function.

bool joinable() const noexcept;

Returns:

Equivalent to return t_.joinable().

Throws:

Nothing

void join();

Effects:

Equivalent to t_.join().

template <class Rep, class Period>
bool try_join_for(const chrono::duration<Rep, Period>& rel_time);

Effects:

Equivalent to return t_.try_join_for(rel_time).

template <class Clock, class Duration>
bool try_join_until(const chrono::time_point<Clock, Duration>& abs_time);

Effects:

Equivalent to return t_.try_join_until(abs_time).

void detach();

Effects:

Equivalent to t_.detach().

thread::id get_id() const noexcept;

Effects:

Equivalent to return t_.get_id().

void interrupt();

Effects:

Equivalent to t_.interrupt().

unsigned hardware_concurrency() noexecpt;

Effects:

Equivalent to return thread::hardware_concurrency().

typedef thread::native_handle_type native_handle_type;
native_handle_type native_handle();

Effects:

Equivalent to return t_.native_handle().

void swap(scoped_thread& other) noexcept;

Effects:

Equivalent t_.swap(other.t_).

#include <boost/thread/scoped_thread.hpp>

void swap(scoped_thread& lhs,scoped_thread& rhs) noexcept;

Effects:

lhs.swap(rhs).


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