tf::Subflow class
#include <taskflow/core/flow_builder.hpp>

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

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(bool flag) noexcept: specifies whether to keep the subflow after it is joined
auto retain() const -> bool: queries if the subflow will be retained after it is joined

Function documentation

void tf::Subflow::join()

enables the subflow to join its parent task

Performs an immediate action to join the subflow. Once the subflow is joined, it is considered finished and you may not modify the subflow anymore.

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

Only the worker that spawns this subflow can join it.

bool tf::Subflow::joinable() const noexcept

queries if the subflow is joinable

This member function queries if the subflow is joinable. When a subflow is joined, it becomes not joinable.

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

void tf::Subflow::retain(bool flag) noexcept

specifies whether to keep the subflow after it is joined

Parameters
flag	`true` to retain the subflow after it is joined; `false` to discard it

By default, the runtime automatically clears a spawned subflow once it is joined. Setting this flag to true allows the application to retain the subflow's structure for post-execution analysis like visualization.

bool tf::Subflow::retain() const

queries if the subflow will be retained after it is joined

Returns	`true` if the subflow will be retained after it is joined; `false` otherwise

tf::Subflow class #include <taskflow/core/flow_builder.hpp>