Reference documentation for deal.II version 9.3.0

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

## Public Member Functions

Thread (const std::function< RT()> &function)

void join () const

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

bool valid () const

bool operator== (const Thread &t) const

## Detailed Description

### template<typename RT = void> class Threads::Thread< RT >

An object that represents a spawned thread. This object can be freely copied around in user space, and all instances will represent the same thread and can require to wait for its termination and access its return value.

Threads can be abandoned, i.e. if you just call Threads::new_thread but don't care about the returned object, or if you assign the return Threads::Thread object to an object that subsequently goes out of scope, then the thread previously created will still continue to do work. You will simply not be able to access its return value any more, and it may also happen that your program terminates before the thread has finished its work.

The default value of the template argument is void, so if the function you are calling on a new thread has no return value, you can omit the template argument.

Deprecated:
Note
Since this class is used in ThreadGroup, its constructors, rather than the class itself, are deprecated to allow compilation with -Werror=deprecated-declarations.

Definition at line 580 of file thread_management.h.

## ◆ Thread() [1/3]

template<typename RT = void>
 Threads::Thread< RT >::Thread ( const std::function< RT()> & function )
inline

Construct a thread object with a function object.

Definition at line 587 of file thread_management.h.

## ◆ Thread() [2/3]

template<typename RT = void>
default

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

## ◆ Thread() [3/3]

template<typename RT = void>
inline

Copy constructor.

Definition at line 606 of file thread_management.h.

## ◆ join()

template<typename RT = void>
 void Threads::Thread< RT >::join ( ) const
inline

Join the thread represented by this object, i.e. wait for it to finish. If you have used the default constructor of this class and have not assigned a thread object to it, then this function is a no-op.

Definition at line 616 of file thread_management.h.

## ◆ return_value()

template<typename RT = void>
inline

Get the return value of the function of the thread. 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
...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()
{
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 thread, it needs to be moved, and in order to be moved, the current function needs to return a writable (non-const) reference.

Definition at line 666 of file thread_management.h.

## ◆ valid()

template<typename RT = void>
 bool Threads::Thread< RT >::valid ( ) const
inline

Return true if this object has had a thread associated with it, either by using the non-default constructor or by assignment.

Definition at line 677 of file thread_management.h.

## ◆ operator==()

template<typename RT = void>
 bool Threads::Thread< RT >::operator== ( const Thread< RT > & t ) const
inline

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

Definition at line 689 of file thread_management.h.