tf::Taskflow Class Reference

class to create a taskflow object More...

#include <taskflow.hpp>

Inheritance diagram for tf::Taskflow:

Collaboration diagram for tf::Taskflow:

Public Member Functions
	Taskflow (const std::string &name)
	constructs a taskflow with the given name
	Taskflow ()
	constructs a taskflow
	Taskflow (Taskflow &&rhs)
	constructs a taskflow from a moved taskflow
Taskflow &	operator= (Taskflow &&rhs)
	move assignment operator
	~Taskflow ()=default
	default destructor
void	dump (std::ostream &ostream) const
	dumps the taskflow to a DOT format through a std::ostream target
std::string	dump () const
	dumps the taskflow to a std::string of DOT format
size_t	num_tasks () const
	queries the number of tasks
bool	empty () const
	queries the emptiness of the taskflow
void	name (const std::string &)
	assigns a name to the taskflow
const std::string &	name () const
	queries the name of the taskflow
void	clear ()
	clears the associated task dependency graph
template<typename V >
void	for_each_task (V &&visitor) const
	applies a visitor to each task in the taskflow
Graph &	graph ()
	returns a reference to the underlying graph object
Public Member Functions inherited from tf::FlowBuilder
	FlowBuilder (Graph &graph)
	constructs a flow builder with a graph
template<typename C , std::enable_if_t< is_static_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a static task
template<typename C , std::enable_if_t< is_dynamic_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a dynamic task
template<typename C , std::enable_if_t< is_condition_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a condition task
template<typename C , std::enable_if_t< is_multi_condition_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a multi-condition task
template<typename... C, std::enable_if_t<(sizeof...(C)>1), void > * = nullptr>
auto	emplace (C &&... callables)
	creates multiple tasks from a list of callable objects
void	erase (Task task)
	removes a task from a taskflow
template<typename T >
Task	composed_of (T &object)
	creates a module task for the target object
Task	placeholder ()
	creates a placeholder task
template<typename C , std::enable_if_t< is_cudaflow_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a cudaFlow task on the caller's GPU device context
template<typename C , typename D , std::enable_if_t< is_cudaflow_task_v< C >, void > * = nullptr>
Task	emplace_on (C &&callable, D &&device)
	creates a cudaFlow task on the given device
template<typename C , std::enable_if_t< is_syclflow_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a syclFlow task on the default queue
template<typename C , typename Q , std::enable_if_t< is_syclflow_task_v< C >, void > * = nullptr>
Task	emplace_on (C &&callable, Q &&queue)
	creates a syclFlow task on the given queue
template<typename C , std::enable_if_t< is_runtime_task_v< C >, void > * = nullptr>
Task	emplace (C &&callable)
	creates a runtime task
void	linearize (std::vector< Task > &tasks)
	adds adjacent dependency links to a linear list of tasks
void	linearize (std::initializer_list< Task > tasks)
	adds adjacent dependency links to a linear list of tasks
template<typename B , typename E , typename C >
Task	for_each (B first, E last, C callable)
	constructs a STL-styled parallel-for task
template<typename B , typename E , typename S , typename C >
Task	for_each_index (B first, E last, S step, C callable)
	constructs a parallel-transform task
template<typename B , typename E , typename O , typename C >
Task	transform (B first1, E last1, O d_first, C c)
	constructs a parallel-transform task
template<typename B1 , typename E1 , typename B2 , typename O , typename C >
Task	transform (B1 first1, E1 last1, B2 first2, O d_first, C c)
	constructs a parallel-transform task
template<typename B , typename E , typename T , typename O >
Task	reduce (B first, E last, T &init, O bop)
	constructs a STL-styled parallel-reduce task
template<typename B , typename E , typename T , typename BOP , typename UOP >
Task	transform_reduce (B first, E last, T &init, BOP bop, UOP uop)
	constructs a STL-styled parallel transform-reduce task
template<typename B , typename E , typename C >
Task	sort (B first, E last, C cmp)
	constructs a dynamic task to perform STL-styled parallel sort
template<typename B , typename E >
Task	sort (B first, E last)
	constructs a dynamic task to perform STL-styled parallel sort using the std::less<T> comparator, where T is the element type

Friends
class	Topology
class	Executor
class	FlowBuilder

Additional Inherited Members
Protected Attributes inherited from tf::FlowBuilder
Graph &	_graph
	associated graph object

Detailed Description

class to create a taskflow object

A taskflow manages a task dependency graph where each task represents a callable object (e.g., lambda, std::function) and an edge represents a dependency between two tasks. A task is one of the following types:

1. static task : the callable constructible from std::function<void()>
2. dynamic task : the callable constructible from std::function<void(tf::Subflow&)>
3. condition task : the callable constructible from std::function<int()>
4. multi-condition task: the callable constructible from std::function<tf::SmallVector<int>()>
5. module task : the task constructed from tf::Taskflow::composed_of
6. runtime task : the callable constructible from std::function<void(tf::Runtime&)>
7. cudaFlow task : the callable constructible from std::function<void(tf::cudaFlow&)> or std::function<void(tf::cudaFlowCapturer&)>
8. syclFlow task : the callable constructible from std::function<void(tf::syclFlow&)>

Each task is a basic computation unit and is run by one worker thread from an executor. The following example creates a simple taskflow graph of four static tasks, A, B, C, and D, where A runs before B and C and D runs after B and C.

tf::Executor executor;
tf::Taskflow taskflow("simple");
 
tf::Task A = taskflow.emplace([](){ std::cout << "TaskA\n"; });
tf::Task B = taskflow.emplace([](){ std::cout << "TaskB\n"; });
tf::Task C = taskflow.emplace([](){ std::cout << "TaskC\n"; });
tf::Task D = taskflow.emplace([](){ std::cout << "TaskD\n"; });
 
A.precede(B, C);  // A runs before B and C
D.succeed(B, C);  // D runs after  B and C
 
executor.run(taskflow).wait();

The taskflow object itself is NOT thread-safe. You should not modifying the graph while it is running, such as adding new tasks, adding new dependencies, and moving the taskflow to another. To minimize the overhead of task creation, our runtime leverages a global object pool to recycle tasks in a thread-safe manner.

Please refer to Cookbook to learn more about each task type and how to submit a taskflow to an executor.

Constructor & Destructor Documentation

Taskflow() [1/2]

tf::Taskflow::Taskflow ( const std::string &  name )

inline

constructs a taskflow with the given name

tf::Taskflow taskflow("My Taskflow");
std::cout << taskflow.name();         // "My Taskflow"

Taskflow() [2/2]

tf::Taskflow::Taskflow ( Taskflow &&  rhs )

inline

constructs a taskflow from a moved taskflow

Constructing a taskflow taskflow1 from a moved taskflow taskflow2 will migrate the graph of taskflow2 to taskflow1. After the move, taskflow2 will become empty.

tf::Taskflow taskflow1(std::move(taskflow2));
assert(taskflow2.empty());

Notice that taskflow2 should not be running in an executor during the move operation, or the behavior is undefined.

~Taskflow()

tf::Taskflow::~Taskflow ( )

default

default destructor

When the destructor is called, all tasks and their associated data (e.g., captured data) will be destroyed. It is your responsibility to ensure all submitted execution of this taskflow have completed before destroying it. For instance, the following code results in undefined behavior since the executor may still be running the taskflow while it is destroyed after the block.

{
  tf::Taskflow taskflow;
  executor.run(taskflow);
}

To fix the problem, we must wait for the execution to complete before destroying the taskflow.

{
  tf::Taskflow taskflow;
  executor.run(taskflow).wait();
}

Member Function Documentation

clear()

void tf::Taskflow::clear ( )

inline

clears the associated task dependency graph

When you clear a taskflow, all tasks and their associated data (e.g., captured data in task callables) will be destroyed. The behavior of clearing a running taskflow is undefined.

dump() [1/2]

std::string tf::Taskflow::dump ( ) const

inline

dumps the taskflow to a std::string of DOT format

This method is similar to tf::Taskflow::dump(std::ostream& ostream), but returning a string of the graph in DOT format.

dump() [2/2]

void tf::Taskflow::dump ( std::ostream &  ostream ) const

inline

dumps the taskflow to a DOT format through a std::ostream target

taskflow.dump(std::cout);  // dump the graph to the standard output
 
std::ofstream ofs("output.dot");
taskflow.dump(ofs);        // dump the graph to the file output.dot

For dynamically spawned tasks, such as module tasks, subflow tasks, and GPU tasks, you need to run the taskflow first before you can dump the entire graph.

tf::Task parent = taskflow.emplace([](tf::Subflow sf){
  sf.emplace([](){ std::cout << "child\n"; });
});
taskflow.dump(std::cout);      // this dumps only the parent tasks
executor.run(taskflow).wait();
taskflow.dump(std::cout);      // this dumps both parent and child tasks

empty()

bool tf::Taskflow::empty ( ) const

inline

queries the emptiness of the taskflow

An empty taskflow has no tasks. That is the return of tf::Taskflow::num_tasks is zero.

for_each_task()

template<typename V >

void tf::Taskflow::for_each_task

(

V &&

visitor

)

const

applies a visitor to each task in the taskflow

A visitor is a callable that takes an argument of type tf::Task and returns nothing. The following example iterates each task in a taskflow and prints its name:

taskflow.for_each_task([](tf::Task task){
  std::cout << task.name() << '\n';
});

graph()

Graph & tf::Taskflow::graph ( )

inline

returns a reference to the underlying graph object

A graph object (of type tf::Graph) is the ultimate storage for the task dependency graph and should only be used as an opaque data structure to interact with the executor (e.g., composition).

name() [1/2]

const std::string & tf::Taskflow::name ( ) const

inline

queries the name of the taskflow

std::cout << "my name is: " << taskflow.name();

name() [2/2]

void tf::Taskflow::name ( const std::string &  name )

inline

assigns a name to the taskflow

taskflow.name("assign another name");

operator=()

Taskflow & tf::Taskflow::operator= ( Taskflow &&  rhs )

inline

move assignment operator

Moving a taskflow taskflow2 to another taskflow taskflow1 will destroy the existing graph of taskflow1 and assign it the graph of taskflow2. After the move, taskflow2 will become empty.

taskflow1 = std::move(taskflow2);
assert(taskflow2.empty());

Notice that both taskflow1 and taskflow2 should not be running in an executor during the move operation, or the behavior is undefined.

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

• core/taskflow.hpp