tf::Subflow class

#include <taskflow/core/flow_builder.hpp>

class to construct a subflow graph from the execution of a dynamic task

Contents

• Reference
  • Base classes
  • Public functions

tf::Subflow is spawned from the execution of a task to dynamically manage a child graph that may depend on runtime variables. You can explicitly join a subflow by calling tf::Subflow::join, respectively. By default, the Taskflow runtime will implicitly join a subflow it is is joinable.

The following example creates a taskflow graph that spawns a subflow from the execution of task B, and the subflow contains three tasks, B1, B2, and B3, where B3 runs after B1 and B2.

// create three static tasks
tf::Task A = taskflow.emplace([](){}).name("A");
tf::Task C = taskflow.emplace([](){}).name("C");
tf::Task D = taskflow.emplace([](){}).name("D");

// create a subflow graph (dynamic tasking)
tf::Task B = taskflow.emplace([] (tf::Subflow& subflow) {
  tf::Task B1 = subflow.emplace([](){}).name("B1");
  tf::Task B2 = subflow.emplace([](){}).name("B2");
  tf::Task B3 = subflow.emplace([](){}).name("B3");
  B1.precede(B3);
  B2.precede(B3);
}).name("B");

A.precede(B);  // B runs after A
A.precede(C);  // C runs after A
B.precede(D);  // D runs after B
C.precede(D);  // D runs after C

Base classes

class FlowBuilder

class to build a task dependency graph

Public functions

void join()

enables the subflow to join its parent task

auto joinable() const -> bool noexcept

queries if the subflow is joinable

auto executor() -> Executor& noexcept

acquires the associated executor

auto graph() -> Graph&

acquires the associated graph

void retain_on_join(bool flag) noexcept

specifies whether to keep the subflow after it is joined

auto retain_on_join() const -> bool

queries if the subflow will be retained after it is joined

Function documentation

taskflow.emplace([](tf::Subflow& sf){
  sf.emplace([](){});
  sf.join();  // join the subflow of one task
});

taskflow.emplace([](tf::Subflow& sf){
  sf.emplace([](){});
  std::cout << sf.joinable() << '\n';  // true
  sf.join();
  std::cout << sf.joinable() << '\n';  // false
});