tf::Executor Class Reference

class to create an executor More...

#include <taskflow/core/executor.hpp>

Public Member Functions
	Executor (size_t N=std::thread::hardware_concurrency(), std::shared_ptr< WorkerInterface > wif=nullptr)
	constructs the executor with N worker threads
	~Executor ()
	destructs the executor
tf::Future< void >	run (Taskflow &taskflow)
	runs a taskflow once
tf::Future< void >	run (Taskflow &&taskflow)
	runs a moved taskflow once
template<typename C>
tf::Future< void >	run (Taskflow &taskflow, C &&callable)
	runs a taskflow once and invoke a callback upon completion
template<typename C>
tf::Future< void >	run (Taskflow &&taskflow, C &&callable)
	runs a moved taskflow once and invoke a callback upon completion
tf::Future< void >	run_n (Taskflow &taskflow, size_t N)
	runs a taskflow for N times
tf::Future< void >	run_n (Taskflow &&taskflow, size_t N)
	runs a moved taskflow for N times
template<typename C>
tf::Future< void >	run_n (Taskflow &taskflow, size_t N, C &&callable)
	runs a taskflow for N times and then invokes a callback
template<typename C>
tf::Future< void >	run_n (Taskflow &&taskflow, size_t N, C &&callable)
	runs a moved taskflow for N times and then invokes a callback
template<typename P>
tf::Future< void >	run_until (Taskflow &taskflow, P &&pred)
	runs a taskflow multiple times until the predicate becomes true
template<typename P>
tf::Future< void >	run_until (Taskflow &&taskflow, P &&pred)
	runs a moved taskflow and keeps running it until the predicate becomes true
template<typename P, typename C>
tf::Future< void >	run_until (Taskflow &taskflow, P &&pred, C &&callable)
	runs a taskflow multiple times until the predicate becomes true and then invokes the callback
template<typename P, typename C>
tf::Future< void >	run_until (Taskflow &&taskflow, P &&pred, C &&callable)
	runs a moved taskflow and keeps running it until the predicate becomes true and then invokes the callback
template<typename T>
void	corun (T &target)
	runs a target graph and waits until it completes using an internal worker of this executor
template<typename P>
void	corun_until (P &&predicate)
	keeps running the work-stealing loop until the predicate returns true
void	wait_for_all ()
	waits for all tasks to complete
size_t	num_workers () const noexcept
	queries the number of worker threads
size_t	num_waiters () const noexcept
	queries the number of workers that are in the waiting loop
size_t	num_queues () const noexcept
	queries the number of work-stealing queues used by the executor
size_t	num_topologies () const
	queries the number of running topologies at the time of this call
Worker *	this_worker ()
	queries pointer to the calling worker if it belongs to this executor, otherwise returns nullptr
int	this_worker_id () const
	queries the id of the caller thread within this executor
template<typename Observer, typename... ArgsT>
std::shared_ptr< Observer >	make_observer (ArgsT &&... args)
	constructs an observer to inspect the activities of worker threads
template<typename Observer>
void	remove_observer (std::shared_ptr< Observer > observer)
	removes an observer from the executor
size_t	num_observers () const noexcept
	queries the number of observers
template<typename P, typename F>
auto	async (P &&params, F &&func)
	creates a parameterized asynchronous task to run the given function
template<typename F>
auto	async (F &&func)
	runs a given function asynchronously
template<typename P, typename F>
void	silent_async (P &&params, F &&func)
	similar to tf::Executor::async but does not return a future object
template<typename F>
void	silent_async (F &&func)
	similar to tf::Executor::async but does not return a future object
template<typename F, typename... Tasks> requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)
tf::AsyncTask	silent_dependent_async (F &&func, Tasks &&... tasks)
	runs the given function asynchronously when the given predecessors finish
template<TaskParameters P, typename F, typename... Tasks> requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)
tf::AsyncTask	silent_dependent_async (P &&params, F &&func, Tasks &&... tasks)
	runs the given function asynchronously when the given predecessors finish
template<typename F, typename I> requires (!std::same_as<std::decay_t<I>, AsyncTask>)
tf::AsyncTask	silent_dependent_async (F &&func, I first, I last)
	runs the given function asynchronously when the given range of predecessors finish
template<TaskParameters P, typename F, typename I> requires (!std::same_as<std::decay_t<I>, AsyncTask>)
tf::AsyncTask	silent_dependent_async (P &&params, F &&func, I first, I last)
	runs the given function asynchronously when the given range of predecessors finish
template<typename F, typename... Tasks> requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)
auto	dependent_async (F &&func, Tasks &&... tasks)
	runs the given function asynchronously when the given predecessors finish
template<TaskParameters P, typename F, typename... Tasks> requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)
auto	dependent_async (P &&params, F &&func, Tasks &&... tasks)
	runs the given function asynchronously when the given predecessors finish
template<typename F, typename I> requires (!std::same_as<std::decay_t<I>, AsyncTask>)
auto	dependent_async (F &&func, I first, I last)
	runs the given function asynchronously when the given range of predecessors finish
template<TaskParameters P, typename F, typename I> requires (!std::same_as<std::decay_t<I>, AsyncTask>)
auto	dependent_async (P &&params, F &&func, I first, I last)
	runs the given function asynchronously when the given range of predecessors finish
TaskGroup	task_group ()
	creates a task group that executes a collection of asynchronous tasks

Friends
class	FlowBuilder
class	Subflow
class	Runtime
class	NonpreemptiveRuntime
class	Algorithm
class	TaskGroup

Detailed Description

class to create an executor

An tf::Executor manages a set of worker threads to run tasks using an efficient work-stealing scheduling algorithm.

// Declare an executor and a taskflow
tf::Executor executor;
tf::Taskflow taskflow;
 
// Add three tasks into the taskflow
tf::Task A = taskflow.emplace([] () { std::cout << "This is TaskA\n"; });
tf::Task B = taskflow.emplace([] () { std::cout << "This is TaskB\n"; });
tf::Task C = taskflow.emplace([] () { std::cout << "This is TaskC\n"; });
 
// Build precedence between tasks
A.precede(B, C);
 
tf::Future<void> fu = executor.run(taskflow);
fu.wait();  // block until the execution completes
 
executor.run(taskflow, [](){ std::cout << "end of 1 run"; }).wait();
executor.run_n(taskflow, 4);
executor.wait_for_all();  // block until all associated executions finish
executor.run_n(taskflow, 4, [](){ std::cout << "end of 4 runs"; }).wait();
executor.run_until(taskflow, [cnt=0] () mutable { return ++cnt == 10; });

Most executor methods are thread-safe. For example, you can submit multiple taskflows to an executor concurrently from different threads, while other threads simultaneously create asynchronous tasks.

std::thread t1([&](){ executor.run(taskflow); };
std::thread t2([&](){ executor.async([](){ std::cout << "async task from t2\n"; }); });
executor.async([&](){ std::cout << "async task from the main thread\n"; });

Note

To know more about tf::Executor, please refer to Executor.

Constructor & Destructor Documentation

Executor()

tf::Executor::Executor ( size_t N = std::thread::hardware_concurrency(), std::shared_ptr< WorkerInterface > wif = nullptr )

explicit

constructs the executor with N worker threads

Parameters

N	number of workers (default std::thread::hardware_concurrency)
wif	interface class instance to configure workers' behaviors

The constructor spawns N worker threads to run tasks in a work-stealing loop. The number of workers must be greater than zero or an exception will be thrown. By default, the number of worker threads is equal to the maximum hardware concurrency returned by std::thread::hardware_concurrency.

Users can alter the worker behavior, such as changing thread affinity, via deriving an instance from tf::WorkerInterface.

Attention

An exception will be thrown if executor construction fails.

~Executor()

tf::Executor::~Executor

(

)

destructs the executor

The destructor calls Executor::wait_for_all to wait for all submitted taskflows to complete and then notifies all worker threads to stop and join these threads.

Member Function Documentation

async() [1/2]

template<typename F>

auto tf::Executor::async

(

F &&

func

)

runs a given function asynchronously

Template Parameters

F	callable type

Parameters

func	callable object

Returns

a std::future that will hold the result of the execution

The method creates an asynchronous task to run the given function and return a std::future object that eventually will hold the result of the return value.

std::future<int> future = executor.async([](){
  std::cout << "create an asynchronous task and returns 1\n";
  return 1;
});
future.get();

This member function is thread-safe.

async() [2/2]

template<typename P, typename F>

auto tf::Executor::async	(	P &&	params,
		F &&	func )

creates a parameterized asynchronous task to run the given function

Template Parameters

P	task parameter type satisfying tf::TaskParameters
F	callable type

Parameters

params	task parameters
func	callable object

Returns

a std::future that will hold the result of the execution

The method creates a parameterized asynchronous task to run the given function and return a std::future object that eventually will hold the result of the execution.

std::future<int> future = executor.async("name", [](){
  std::cout << "create an asynchronous task with a name and returns 1\n";
  return 1;
});
future.get();

This member function is thread-safe.

corun()

template<typename T>

void tf::Executor::corun

(

T &

target

)

runs a target graph and waits until it completes using an internal worker of this executor

Template Parameters

T	target type which is either convertible to tf::Graph or has tf::Graph& T::graph() defined

Parameters

target

the target task graph object

The method coruns a target graph cooperatively with other workers in the same executor and block until the execution completes. Under cooperative execution, a worker is not preempted. Instead, it continues participating in the work-stealing loop, executing available tasks alongside other workers.

tf::Executor executor(2);
tf::Taskflow taskflow;
std::array<tf::Taskflow, 1000> others;
 
std::atomic<size_t> counter{0};
 
for(size_t n=0; n<1000; n++) {
  for(size_t i=0; i<1000; i++) {
    others[n].emplace([&](){ counter++; });
  }
  taskflow.emplace([&executor, &tf=others[n]](){
    executor.corun(tf);
    //executor.run(tf).wait();  <- blocking the worker without doing anything
    //                             will introduce deadlock
  });
}
executor.run(taskflow).wait();

The method is thread-safe as long as the target is not concurrently ran by two or more threads.

Attention

You must call tf::Executor::corun from a worker of the calling executor or an exception will be thrown.

corun_until()

template<typename P>

void tf::Executor::corun_until

(

P &&

predicate

)

keeps running the work-stealing loop until the predicate returns true

Template Parameters

P	predicate type

Parameters

predicate

a boolean predicate to indicate when to stop the loop

The method keeps the caller worker running in the work-stealing loop until the stop predicate becomes true.

The method keeps the calling worker running available tasks cooperatively with other workers in the same executor and block until the predicate return true. Under cooperative execution, a worker is not preempted. Instead, it continues participating in the work-stealing loop, executing available tasks alongside other workers.

taskflow.emplace([&](){
  std::future<void> fu = std::async([](){ std::sleep(100s); });
  executor.corun_until([](){
    return fu.wait_for(std::chrono::seconds(0)) == future_status::ready;
  });
});

Attention

You must call tf::Executor::corun_until from a worker of the calling executor or an exception will be thrown.

dependent_async() [1/4]

template<typename F, typename I>
requires (!std::same_as<std::decay_t<I>, AsyncTask>)

auto tf::Executor::dependent_async	(	F &&	func,
		I	first,
		I	last )

runs the given function asynchronously when the given range of predecessors finish

Template Parameters

F	callable type
I	iterator type

Parameters

func	callable object
first	iterator to the beginning (inclusive)
last	iterator to the end (exclusive)

Returns

a pair of a tf::AsyncTask handle and a std::future that holds the result of the execution

The example below creates three asynchronous tasks, A, B, and C, in which task C runs after task A and task B. Task C returns a pair of its tf::AsyncTask handle and a std::future<int> that eventually will hold the result of the execution.

std::array<tf::AsyncTask, 2> array {
  executor.silent_dependent_async([](){ printf("A\n"); }),
  executor.silent_dependent_async([](){ printf("B\n"); })
};
auto [C, fuC] = executor.dependent_async(
  [](){ 
    printf("C runs after A and B\n"); 
    return 1;
  }, 
  array.begin(), array.end()
);
assert(fuC.get()==1);  // C finishes, which in turns means both A and B finish

You can mix the use of tf::AsyncTask handles returned by tf::Executor::dependent_async and tf::Executor::silent_dependent_async when specifying task dependencies.

This member function is thread-safe.

dependent_async() [2/4]

template<typename F, typename... Tasks>
requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)

auto tf::Executor::dependent_async	(	F &&	func,
		Tasks &&...	tasks )

runs the given function asynchronously when the given predecessors finish

Template Parameters

F	callable type
Tasks	task types convertible to tf::AsyncTask

Parameters

func	callable object
tasks	asynchronous tasks on which this execution depends

Returns

a pair of a tf::AsyncTask handle and a std::future that holds the result of the execution

The example below creates three asynchronous tasks, A, B, and C, in which task C runs after task A and task B. Task C returns a pair of its tf::AsyncTask handle and a std::future<int> that eventually will hold the result of the execution.

tf::AsyncTask A = executor.silent_dependent_async([](){ printf("A\n"); });
tf::AsyncTask B = executor.silent_dependent_async([](){ printf("B\n"); });
auto [C, fuC] = executor.dependent_async(
  [](){ 
    printf("C runs after A and B\n"); 
    return 1;
  }, 
  A, B
);
fuC.get();  // C finishes, which in turns means both A and B finish

You can mix the use of tf::AsyncTask handles returned by tf::Executor::dependent_async and tf::Executor::silent_dependent_async when specifying task dependencies.

This member function is thread-safe.

dependent_async() [3/4]

template<TaskParameters P, typename F, typename I>
requires (!std::same_as<std::decay_t<I>, AsyncTask>)

auto tf::Executor::dependent_async	(	P &&	params,
		F &&	func,
		I	first,
		I	last )

runs the given function asynchronously when the given range of predecessors finish

Template Parameters

P	task parameters type satisfying tf::TaskParameters
F	callable type
I	iterator type

Parameters

params	task parameters
func	callable object
first	iterator to the beginning (inclusive)
last	iterator to the end (exclusive)

Returns

a pair of a tf::AsyncTask handle and a std::future that holds the result of the execution

The example below creates three named asynchronous tasks, A, B, and C, in which task C runs after task A and task B. Task C returns a pair of its tf::AsyncTask handle and a std::future<int> that eventually will hold the result of the execution. Assigned task names will appear in the observers of the executor.

std::array<tf::AsyncTask, 2> array {
  executor.silent_dependent_async("A", [](){ printf("A\n"); }),
  executor.silent_dependent_async("B", [](){ printf("B\n"); })
};
auto [C, fuC] = executor.dependent_async(
  "C",
  [](){ 
    printf("C runs after A and B\n"); 
    return 1;
  }, 
  array.begin(), array.end()
);
assert(fuC.get()==1);  // C finishes, which in turns means both A and B finish

You can mix the use of tf::AsyncTask handles returned by tf::Executor::dependent_async and tf::Executor::silent_dependent_async when specifying task dependencies.

This member function is thread-safe.

dependent_async() [4/4]

template<TaskParameters P, typename F, typename... Tasks>
requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)

auto tf::Executor::dependent_async	(	P &&	params,
		F &&	func,
		Tasks &&...	tasks )

runs the given function asynchronously when the given predecessors finish

Template Parameters

P	task parameters type satisfying tf::TaskParameters
F	callable type
Tasks	task types convertible to tf::AsyncTask

Parameters

params	task parameters
func	callable object
tasks	asynchronous tasks on which this execution depends

Returns

a pair of a tf::AsyncTask handle and a std::future that holds the result of the execution

The example below creates three named asynchronous tasks, A, B, and C, in which task C runs after task A and task B. Task C returns a pair of its tf::AsyncTask handle and a std::future<int> that eventually will hold the result of the execution. Assigned task names will appear in the observers of the executor.

tf::AsyncTask A = executor.silent_dependent_async("A", [](){ printf("A\n"); });
tf::AsyncTask B = executor.silent_dependent_async("B", [](){ printf("B\n"); });
auto [C, fuC] = executor.dependent_async(
  "C",
  [](){ 
    printf("C runs after A and B\n"); 
    return 1;
  }, 
  A, B
);
assert(fuC.get()==1);  // C finishes, which in turns means both A and B finish

You can mix the use of tf::AsyncTask handles returned by tf::Executor::dependent_async and tf::Executor::silent_dependent_async when specifying task dependencies.

This member function is thread-safe.

make_observer()

template<typename Observer, typename... ArgsT>

std::shared_ptr< Observer > tf::Executor::make_observer

(

ArgsT &&...

args

)

constructs an observer to inspect the activities of worker threads

Template Parameters

Observer	observer type derived from tf::ObserverInterface
ArgsT	argument parameter pack

Parameters

args	arguments to forward to the constructor of the observer

Returns

a shared pointer to the created observer

Each executor manages a list of observers with shared ownership with callers. For each of these observers, the two member functions, tf::ObserverInterface::on_entry and tf::ObserverInterface::on_exit will be called before and after the execution of a task.

This member function is not thread-safe.

num_topologies()

size_t tf::Executor::num_topologies

(

)

const

queries the number of running topologies at the time of this call

When a taskflow is submitted to an executor, a topology is created to store runtime metadata of the running taskflow. When the execution of the submitted taskflow finishes, its corresponding topology will be removed from the executor.

executor.run(taskflow);
std::cout << executor.num_topologies();  // 0 or 1 (taskflow still running)

num_waiters()

size_t tf::Executor::num_waiters ( ) const

noexcept

queries the number of workers that are in the waiting loop

A worker in the waiting loop has exhausted its local queue and made enough stealing attempts, and is now ready to be preempted and enter the waiting state.

num_workers()

size_t tf::Executor::num_workers ( ) const

noexcept

queries the number of worker threads

Each worker represents a unique thread spawned by an executor upon its construction time.

tf::Executor executor(4);
std::cout << executor.num_workers();    // 4

remove_observer()

template<typename Observer>

void tf::Executor::remove_observer

(

std::shared_ptr< Observer >

observer

)

removes an observer from the executor

This member function is not thread-safe.

run() [1/4]

tf::Future< void > tf::Executor::run

(

Taskflow &&

taskflow

)

runs a moved taskflow once

Parameters

taskflow

a moved tf::Taskflow object

Returns

a tf::Future that holds the result of the execution

This member function executes a moved taskflow once and returns a tf::Future object that eventually holds the result of the execution. The executor will take care of the lifetime of the moved taskflow.

tf::Future<void> future = executor.run(std::move(taskflow));
// do something else
future.wait();

This member function is thread-safe.

run() [2/4]

template<typename C>

tf::Future< void > tf::Executor::run	(	Taskflow &&	taskflow,
		C &&	callable )

runs a moved taskflow once and invoke a callback upon completion

Parameters

taskflow	a moved tf::Taskflow object
callable	a callable object to be invoked after this run

Returns

a tf::Future that holds the result of the execution

This member function executes a moved taskflow once and invokes the given callable when the execution completes. This member function returns a tf::Future object that eventually holds the result of the execution. The executor will take care of the lifetime of the moved taskflow.

tf::Future<void> future = executor.run(
  std::move(taskflow), [](){ std::cout << "done"; }
);
// do something else
future.wait();

This member function is thread-safe.

run() [3/4]

tf::Future< void > tf::Executor::run

(

Taskflow &

taskflow

)

runs a taskflow once

Parameters

taskflow

a tf::Taskflow object

Returns

a tf::Future that holds the result of the execution

This member function executes the given taskflow once and returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run(taskflow);
// do something else
future.wait();

This member function is thread-safe.

run() [4/4]

template<typename C>

tf::Future< void > tf::Executor::run	(	Taskflow &	taskflow,
		C &&	callable )

runs a taskflow once and invoke a callback upon completion

Parameters

taskflow	a tf::Taskflow object
callable	a callable object to be invoked after this run

Returns

a tf::Future that holds the result of the execution

This member function executes the given taskflow once and invokes the given callable when the execution completes. This member function returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run(taskflow, [](){ std::cout << "done"; });
// do something else
future.wait();

This member function is thread-safe.

run_n() [1/4]

tf::Future< void > tf::Executor::run_n	(	Taskflow &&	taskflow,
		size_t	N )

runs a moved taskflow for N times

Parameters

taskflow	a moved tf::Taskflow object
N	number of runs

Returns

a tf::Future that holds the result of the execution

This member function executes a moved taskflow N times and returns a tf::Future object that eventually holds the result of the execution. The executor will take care of the lifetime of the moved taskflow.

tf::Future<void> future = executor.run_n(
  std::move(taskflow), 2    // run the moved taskflow 2 times
);
// do something else
future.wait();

This member function is thread-safe.

run_n() [2/4]

template<typename C>

tf::Future< void > tf::Executor::run_n	(	Taskflow &&	taskflow,
		size_t	N,
		C &&	callable )

runs a moved taskflow for N times and then invokes a callback

Parameters

taskflow	a moved tf::Taskflow
N	number of runs
callable	a callable object to be invoked after this run

Returns

a tf::Future that holds the result of the execution

This member function executes a moved taskflow N times and invokes the given callable when the execution completes. This member function returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run_n(
  // run the moved taskflow 2 times and invoke the lambda to print "done"
  std::move(taskflow), 2, [](){ std::cout << "done"; }
);
// do something else
future.wait();

This member function is thread-safe.

run_n() [3/4]

tf::Future< void > tf::Executor::run_n	(	Taskflow &	taskflow,
		size_t	N )

runs a taskflow for N times

Parameters

taskflow	a tf::Taskflow object
N	number of runs

Returns

a tf::Future that holds the result of the execution

This member function executes the given taskflow N times and returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run_n(taskflow, 2);  // run taskflow 2 times
// do something else
future.wait();

This member function is thread-safe.

run_n() [4/4]

template<typename C>

tf::Future< void > tf::Executor::run_n	(	Taskflow &	taskflow,
		size_t	N,
		C &&	callable )

runs a taskflow for N times and then invokes a callback

Parameters

taskflow	a tf::Taskflow
N	number of runs
callable	a callable object to be invoked after this run

Returns

a tf::Future that holds the result of the execution

This member function executes the given taskflow N times and invokes the given callable when the execution completes. This member function returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run(
  taskflow, 2, [](){ std::cout << "done"; }  // runs taskflow 2 times and invoke
                                             // the lambda to print "done"
);
// do something else
future.wait();

This member function is thread-safe.

run_until() [1/4]

template<typename P>

tf::Future< void > tf::Executor::run_until	(	Taskflow &&	taskflow,
		P &&	pred )

runs a moved taskflow and keeps running it until the predicate becomes true

Parameters

taskflow	a moved tf::Taskflow object
pred	a boolean predicate to return true for stop

Returns

a tf::Future that holds the result of the execution

This member function executes a moved taskflow multiple times until the predicate returns true. This member function returns a tf::Future object that eventually holds the result of the execution. The executor will take care of the lifetime of the moved taskflow.

tf::Future<void> future = executor.run_until(
  std::move(taskflow), [](){ return rand()%10 == 0 }
);
// do something else
future.wait();

This member function is thread-safe.

run_until() [2/4]

template<typename P, typename C>

tf::Future< void > tf::Executor::run_until	(	Taskflow &&	taskflow,
		P &&	pred,
		C &&	callable )

runs a moved taskflow and keeps running it until the predicate becomes true and then invokes the callback

Parameters

taskflow	a moved tf::Taskflow
pred	a boolean predicate to return true for stop
callable	a callable object to be invoked after this run completes

Returns

a tf::Future that holds the result of the execution

This member function executes a moved taskflow multiple times until the predicate returns true and then invokes the given callable when the execution completes. This member function returns a tf::Future object that eventually holds the result of the execution. The executor will take care of the lifetime of the moved taskflow.

tf::Future<void> future = executor.run_until(
  std::move(taskflow),
  [](){ return rand()%10 == 0 }, [](){ std::cout << "done"; }
);
// do something else
future.wait();

This member function is thread-safe.

run_until() [3/4]

template<typename P>

tf::Future< void > tf::Executor::run_until	(	Taskflow &	taskflow,
		P &&	pred )

runs a taskflow multiple times until the predicate becomes true

Parameters

taskflow	a tf::Taskflow
pred	a boolean predicate to return true for stop

Returns

a tf::Future that holds the result of the execution

This member function executes the given taskflow multiple times until the predicate returns true. This member function returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run_until(
  taskflow, [](){ return rand()%10 == 0 }
);
// do something else
future.wait();

This member function is thread-safe.

run_until() [4/4]

template<typename P, typename C>

tf::Future< void > tf::Executor::run_until	(	Taskflow &	taskflow,
		P &&	pred,
		C &&	callable )

runs a taskflow multiple times until the predicate becomes true and then invokes the callback

Parameters

taskflow	a tf::Taskflow
pred	a boolean predicate to return true for stop
callable	a callable object to be invoked after this run completes

Returns

a tf::Future that holds the result of the execution

This member function executes the given taskflow multiple times until the predicate returns true and then invokes the given callable when the execution completes. This member function returns a tf::Future object that eventually holds the result of the execution.

tf::Future<void> future = executor.run_until(
  taskflow, [](){ return rand()%10 == 0 }, [](){ std::cout << "done"; }
);
// do something else
future.wait();

This member function is thread-safe.

silent_async() [1/2]

template<typename F>

void tf::Executor::silent_async

(

F &&

func

)

similar to tf::Executor::async but does not return a future object

Template Parameters

F	callable type

Parameters

func	callable object

The method creates an asynchronous task to run the given function without returning any std::future object. This member function is more efficient than tf::Executor::async and is encouraged to use when applications do not need a std::future to acquire the result or synchronize the execution.

executor.silent_async([](){
  std::cout << "create an asynchronous task with no return\n";
});
executor.wait_for_all();

This member function is thread-safe.

silent_async() [2/2]

template<typename P, typename F>

void tf::Executor::silent_async	(	P &&	params,
		F &&	func )

similar to tf::Executor::async but does not return a future object

Template Parameters

F	callable type

Parameters

params	task parameters
func	callable object

The method creates a parameterized asynchronous task to run the given function without returning any std::future object. This member function is more efficient than tf::Executor::async and is encouraged to use when applications do not need a std::future to acquire the result or synchronize the execution.

executor.silent_async("name", [](){
  std::cout << "create an asynchronous task with a name and no return\n";
});
executor.wait_for_all();

This member function is thread-safe.

silent_dependent_async() [1/4]

template<typename F, typename I>
requires (!std::same_as<std::decay_t<I>, AsyncTask>)

tf::AsyncTask tf::Executor::silent_dependent_async	(	F &&	func,
		I	first,
		I	last )

runs the given function asynchronously when the given range of predecessors finish

Template Parameters

F	callable type
I	iterator type

Parameters

func	callable object
first	iterator to the beginning (inclusive)
last	iterator to the end (exclusive)

Returns

a tf::AsyncTask handle

This member function is more efficient than tf::Executor::dependent_async and is encouraged to use when you do not want a std::future to acquire the result or synchronize the execution. The example below creates three asynchronous tasks, A, B, and C, in which task C runs after task A and task B.

std::array<tf::AsyncTask, 2> array {
  executor.silent_dependent_async([](){ printf("A\n"); }),
  executor.silent_dependent_async([](){ printf("B\n"); })
};
executor.silent_dependent_async(
  [](){ printf("C runs after A and B\n"); }, array.begin(), array.end()
);
executor.wait_for_all();

This member function is thread-safe.

silent_dependent_async() [2/4]

template<typename F, typename... Tasks>
requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)

tf::AsyncTask tf::Executor::silent_dependent_async	(	F &&	func,
		Tasks &&...	tasks )

runs the given function asynchronously when the given predecessors finish

Template Parameters

F	callable type
Tasks	task types convertible to tf::AsyncTask

Parameters

func	callable object
tasks	asynchronous tasks on which this execution depends

Returns

a tf::AsyncTask handle

This member function is more efficient than tf::Executor::dependent_async and is encouraged to use when you do not want a std::future to acquire the result or synchronize the execution. The example below creates three asynchronous tasks, A, B, and C, in which task C runs after task A and task B.

tf::AsyncTask A = executor.silent_dependent_async([](){ printf("A\n"); });
tf::AsyncTask B = executor.silent_dependent_async([](){ printf("B\n"); });
executor.silent_dependent_async([](){ printf("C runs after A and B\n"); }, A, B);
executor.wait_for_all();

This member function is thread-safe.

silent_dependent_async() [3/4]

template<TaskParameters P, typename F, typename I>
requires (!std::same_as<std::decay_t<I>, AsyncTask>)

tf::AsyncTask tf::Executor::silent_dependent_async	(	P &&	params,
		F &&	func,
		I	first,
		I	last )

runs the given function asynchronously when the given range of predecessors finish

Template Parameters

F	callable type
I	iterator type

Parameters

params	tasks parameters
func	callable object
first	iterator to the beginning (inclusive)
last	iterator to the end (exclusive)

Returns

a tf::AsyncTask handle

This member function is more efficient than tf::Executor::dependent_async and is encouraged to use when you do not want a std::future to acquire the result or synchronize the execution. The example below creates three asynchronous tasks, A, B, and C, in which task C runs after task A and task B. Assigned task names will appear in the observers of the executor.

std::array<tf::AsyncTask, 2> array {
  executor.silent_dependent_async("A", [](){ printf("A\n"); }),
  executor.silent_dependent_async("B", [](){ printf("B\n"); })
};
executor.silent_dependent_async(
  "C", [](){ printf("C runs after A and B\n"); }, array.begin(), array.end()
);
executor.wait_for_all();

This member function is thread-safe.

silent_dependent_async() [4/4]

template<TaskParameters P, typename F, typename... Tasks>
requires (std::same_as<std::decay_t<Tasks>, AsyncTask> && ...)

tf::AsyncTask tf::Executor::silent_dependent_async	(	P &&	params,
		F &&	func,
		Tasks &&...	tasks )

runs the given function asynchronously when the given predecessors finish

Template Parameters

F	callable type
Tasks	task types convertible to tf::AsyncTask

Parameters

params	task parameters
func	callable object
tasks	asynchronous tasks on which this execution depends

Returns

a tf::AsyncTask handle

This member function is more efficient than tf::Executor::dependent_async and is encouraged to use when you do not want a std::future to acquire the result or synchronize the execution. The example below creates three asynchronous tasks, A, B, and C, in which task C runs after task A and task B. Assigned task names will appear in the observers of the executor.

tf::AsyncTask A = executor.silent_dependent_async("A", [](){ printf("A\n"); });
tf::AsyncTask B = executor.silent_dependent_async("B", [](){ printf("B\n"); });
executor.silent_dependent_async(
  "C", [](){ printf("C runs after A and B\n"); }, A, B
);
executor.wait_for_all();

This member function is thread-safe.

task_group()

TaskGroup tf::Executor::task_group ( )

inline

creates a task group that executes a collection of asynchronous tasks

Returns

a tf::TaskGroup object associated with the current executor

A TaskGroup allows submitting multiple asynchronous tasks to the executor and waiting for their completion collectively using corun(). Tasks added to the group can execute in parallel and may capture local variables by value or reference, depending on your needs. This can be useful for divide-and-conquer algorithms, parallel loops, or any workflow that requires grouping related tasks.

Example (computing Fibonacci numbers in parallel):

tf::Executor executor;
 
size_t fibonacci(size_t N) {
 
  if (N < 2) return N;
 
  size_t res1, res2;
 
  // Create a task group from the current executor
  tf::TaskGroup tg = get_executor().task_group();
 
  // Submit asynchronous tasks to the group
  tg.silent_async([N, &res1](){ res1 = fibonacci(N-1); });
  res2 = fibonacci(N-2);  // compute one branch synchronously
 
  // Wait for all tasks in the group to complete
  tg.corun();
 
  return res1 + res2;
}
 
int main() {
  return executor.async([](){ return fibonacci(30); }).get();
}

This member function is thread-safe.

Attention

Due to cooperative execution, a task group can only be created by a worker of an executor.

this_worker()

Worker * tf::Executor::this_worker

(

)

queries pointer to the calling worker if it belongs to this executor, otherwise returns nullptr

Returns a pointer to the per-worker storage associated with this executor. If the calling thread is not a worker of this executor, the function returns nullptr.

auto w = executor.this_worker();
tf::Taskflow taskflow;
tf::Executor executor;
executor.async([&](){
  assert(executor.this_worker() != nullptr);
  assert(executor.this_worker()->executor() == &executor);
});

this_worker_id()

int tf::Executor::this_worker_id

(

)

const

queries the id of the caller thread within this executor

Each worker has an unique id in the range of 0 to N-1 associated with its parent executor. If the caller thread does not belong to the executor, -1 is returned.

tf::Executor executor(4);   // 4 workers in the executor
executor.this_worker_id();  // -1 (main thread is not a worker)
 
taskflow.emplace([&](){
  std::cout << executor.this_worker_id();  // 0, 1, 2, or 3
});
executor.run(taskflow);

wait_for_all()

void tf::Executor::wait_for_all

(

)

waits for all tasks to complete

This member function waits until all submitted tasks (e.g., taskflows, asynchronous tasks) to finish.

executor.run(taskflow1);
executor.run_n(taskflow2, 10);
executor.run_n(taskflow3, 100);
executor.wait_for_all();  // wait until the above submitted taskflows finish

---

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

• taskflow/core/executor.hpp
• taskflow/core/runtime.hpp
• taskflow/core/task_group.hpp