Threads::Task< RT > Class Template Reference

#include <deal.II/base/thread_management.h>

Public Member Functions
	Task (const std::function< RT()> &function_object)
	Task ()=default
void	join () const
bool	joinable () const
internal::return_value< RT >::reference_type	return_value ()
bool	operator== (const Task &t) const

Static Public Member Functions
static ::ExceptionBase &	ExcNoTask ()

Private Attributes
std::shared_ptr< internal::TaskDescriptor< RT > >	task_descriptor

Detailed Description

template<typename RT = void>
class Threads::Task< RT >

Describes one task object based on the Threading Building Blocks' Task. Note that the call to join() must be executed on the same thread as the call to the constructor. Otherwise, there might be a deadlock. In other words, a Task object should never passed on to another task for calling the join() method.

Author

Wolfgang Bangerth, 2009

Definition at line 1185 of file thread_management.h.

Constructor & Destructor Documentation

Task() [1/2]

template<typename RT = void>

Threads::Task< RT >::Task ( const std::function< RT()> &  function_object )

inline

Construct a task object given a function object to execute on the task, and then schedule this function for execution.

Postcondition

Using this constructor automatically makes the task object joinable().

Definition at line 1506 of file thread_management.h.

Task() [2/2]

template<typename RT = void>

Threads::Task< RT >::Task ( )

default

Default constructor. You can't do much with a task object constructed this way, except for assigning it a task object that holds data created by the Threads::new_task() functions.

Postcondition

Using this constructor leaves the object in an unjoinable state, i.e., joinable() will return false.

Member Function Documentation

join()

template<typename RT = void>

void Threads::Task< RT >::join ( ) const

inline

Join the task represented by this object, i.e. wait for it to finish.

A task can be joined multiple times (while the first join() operation may block until the task has completed running, all successive attempts to join will return immediately).

Precondition

You can't call this function if you have used the default constructor of this class and have not assigned a task object to it. In other words, the function joinable() must return true.

Definition at line 1541 of file thread_management.h.

joinable()

template<typename RT = void>

bool Threads::Task< RT >::joinable ( ) const

inline

Return whether the current object can be joined. You can join a task object once a task (typically created with Threads::new_task()) has actually been assigned to it. On the other hand, the function returns false if the object has been default constructed.

A task can be joined multiple times (while the first join() operation may block until the task has completed running, all successive attempts to join will return immediately). Consequently, if this function returns true, it will continue to return true until the task object it reports on is assigned to from another object.

Definition at line 1560 of file thread_management.h.

return_value()

template<typename RT = void>

internal::return_value<RT>::reference_type Threads::Task< RT >::return_value ( )

inline

Get the return value of the function of the task. Since it is only available once the thread finishes, this function internally also calls join(). You can call this function multiple times as long as the object refers to the same task, and expect to get the same return value every time. (With the exception of the case where the returned object has been moved; see below.)

Note

The function returns a non-const reference to the returned object, instead of the returned object. This allows writing code such as

  Threads::Task<int> t = Threads::new_task (...function returning an
int...); t.return_value() = 42;      // overwrite returned value int i =
t.return_value();   // i is now 42

You will rarely have a need to write such code. On the other hand, the function needs to return a writable (non-const) reference to support code such as this:

std::unique_ptr<int> create_int (const std::string &s) { ... }

void f()
{
  Threads::Task<std::unique_ptr<int>>
    t = Threads::new_task (&create_int, "42");

  std::unique_ptr<int> i = std::move(t.return_value());
  ...
}

Here, it is necessary to std::move the returned object (namely, the std::unique_ptr object) because std::unique_ptr objects can not be copied. In other words, to get the pointer out of the object returned from the task, it needs to be moved, and in order to be moved, the current function needs to return a writable (non-const) reference.

Precondition

You can't call this function if you have used the default constructor of this class and have not assigned a task object to it. In other words, the function joinable() must return true.

Definition at line 1611 of file thread_management.h.

operator==()

template<typename RT = void>

bool Threads::Task< RT >::operator== ( const Task< RT > &  t ) const

inline

Check for equality of task objects. Since objects of this class store an implicit pointer to an object that exists exactly once for each task, the check is simply to compare these pointers.

Definition at line 1624 of file thread_management.h.

Member Data Documentation

task_descriptor

template<typename RT = void>

std::shared_ptr<internal::TaskDescriptor<RT> > Threads::Task< RT >::task_descriptor

private

Shared pointer to the object representing the task. This makes sure that the object lives as long as there is at least one subscriber to it.

Definition at line 1648 of file thread_management.h.

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The documentation for this class was generated from the following file:

• deal.II/base/thread_management.h