tf::RuntimeTaskLike Concept Reference

determines if a callable is a runtime task More...

#include <taskflow/core/task.hpp>

Concept definition

template<typename C>
concept tf::RuntimeTaskLike = 
  (std::invocable<C, tf::Runtime&> &&
   std::same_as<std::invoke_result_t<C, tf::Runtime&>, void>) ||
  (std::invocable<C, tf::NonpreemptiveRuntime&> &&
   std::same_as<std::invoke_result_t<C, tf::NonpreemptiveRuntime&>, void>)

Detailed Description

determines if a callable is a runtime task

A runtime task is a callable object that accepts either tf::Runtime& or tf::NonpreemptiveRuntime& and returns void. Runtime tasks provide access to the executor's runtime information, allowing tasks to spawn work at runtime, query the running state, and control execution flow.

Requirements

• Must be invocable with either tf::Runtime& OR tf::NonpreemptiveRuntime&
• Must return void

Examples

// Valid runtime tasks (satisfy RuntimeTaskLike)
 
// Runtime task with tf::Runtime
auto runtime_task1 = [](tf::Runtime& rt) {
  std::cout << "running with " << rt.num_workers() << " workers\n";
};
static_assert(RuntimeTaskLike<decltype(runtime_task1)>);
 
// Runtime task with tf::NonpreemptiveRuntime
auto runtime_task2 = [](tf::NonpreemptiveRuntime& rt) {
  std::cout << "non-preemptive runtime\n";
};
static_assert(RuntimeTaskLike<decltype(runtime_task2)>);
 
// Runtime task spawning nested work
auto spawn_work = [](tf::Runtime& rt) {
  // Can query and control execution at runtime
  rt.spawn([](){ std::cout << "spawned task\n"; });
};
static_assert(RuntimeTaskLike<decltype(spawn_work)>);
 
// Function object
struct RuntimeTask {
  void operator()(tf::Runtime& rt) const {
    std::cout << "runtime task\n";
  }
};
static_assert(RuntimeTaskLike<RuntimeTask>);
 
// Use in taskflow
tf::Taskflow taskflow;
auto task = taskflow.emplace(runtime_task1).name("runtime");

Invalid Examples

// Invalid: no parameters
auto not_runtime1 = []() { std::cout << "no params\n"; };
// static_assert(RuntimeTaskLike<decltype(not_runtime1)>);  // FAILS
 
// Invalid: wrong parameter type
auto not_runtime2 = [](int x) { std::cout << x << '\n'; };
// static_assert(RuntimeTaskLike<decltype(not_runtime2)>);  // FAILS
 
// Invalid: returns non-void
auto not_runtime3 = [](tf::Runtime& rt) { return 42; };
// static_assert(RuntimeTaskLike<decltype(not_runtime3)>);  // FAILS