ContextQMD
Back to Taskflow

Taskflow: A General

docs/structhash.html

4.1.06.0 KB
Original Source

| | Taskflow: A General-purpose Task-parallel Programming System |

Loading...

Searching...

No Matches

hash Struct Reference

hash specialization for std::hash<tf::Task> More...

#include <taskflow/core/task.hpp>

Detailed Description

hash specialization for std::hash<tf::Task>

hash specialization for std::hash<tf::TaskView>

The hash value of a tf::Task is computed based on the underlying task node pointer. Two tf::Task objects have the same hash value if and only if they reference the same underlying node in the taskflow graph.

Equality and Inequality

Two tf::Task objects are:

  • Equal in hash : when they reference the same task node (same pointer)
  • Unequal in hash : when they reference different task nodes

tf::Task objects created from different taskflow calls or different task insertions will have different hash values, even if they represent logically similar work. The hash function is based on the associated object identity (i.e., underlying node pointer), not semantic equivalence.

tf::Taskflow taskflow;

// Create two tasks

tf::Task task1 = taskflow.emplace( { std::cout << "Task 1\n"; });

tf::Task task2 = taskflow.emplace( { std::cout << "Task 2\n"; });

// Create a copy reference to task1

tf::Task task1_copy = task1;

// Hash values

assert(std::hash<tf::Task>{}(task1) == std::hash<tf::Task>{}(task1_copy));

// task1 and task1_copy reference the same node → same hash

assert(std::hash<tf::Task>{}(task1) != std::hash<tf::Task>{}(task2));

// task1 and task2 are different nodes → different hashes

// Use in hash-based containers

std::unordered_set<tf::Task> task_set;

task_set.insert(task1);

task_set.insert(task2);

assert(task_set.size() == 2); // Both tasks stored

task_set.insert(task1_copy);

assert(task_set.size() == 2); // task1_copy is same node as task1, no new insertion

tf::FlowBuilder::emplace

Task emplace(C &&callable)

creates a static task

Definition flow_builder.hpp:1571

tf::Task

class to create a task handle over a taskflow node

Definition task.hpp:569

tf::Taskflow

class to create a taskflow object

Definition taskflow.hpp:64

See alsotf::Task::hash_value() for obtaining the hash value directly.

The hash value of a tf::TaskView is computed based on the underlying task node address. Two tf::TaskView objects have the same hash value if and only if they reference the same underlying node in the taskflow graph. The hash function is based on the associated object identity (i.e., underlying node pointer), not semantic equivalence.

Equality and Inequality

Two tf::TaskView objects are:

  • Equal in hash : when they reference the same task node
  • Unequal in hash : when they reference different task nodes

Since tf::TaskView is a lightweight read-only view (typically passed by reference or returned by graph traversal functions), hash equality follows the same node identity principle as tf::Task: it depends on which task node is being viewed, not on any semantic property of the task.

tf::Taskflow taskflow;

tf::Task task1 = taskflow.emplace( {});

tf::Task task2 = taskflow.emplace( {});

// TaskView can be created from Task (implicit conversion)

tf::TaskView view1 = task1;

tf::TaskView view2 = task2;

tf::TaskView view1_copy = task1; // Another view of the same node

// Hash values

assert(std::hash<tf::TaskView>{}(view1) == std::hash<tf::TaskView>{}(view1_copy));

// Both views reference the same node → same hash

assert(std::hash<tf::TaskView>{}(view1) != std::hash<tf::TaskView>{}(view2));

// Different nodes → different hashes

// TaskView and Task hash to the same value for the same node

assert(std::hash<tf::TaskView>{}(view1) == std::hash<tf::Task>{}(task1));

// view1 and task1 reference the same node → same hash

// Use in hash-based containers

std::unordered_map<tf::TaskView, int> task_map;

task_map[view1] = 10;

task_map[view2] = 20;

assert(task_map[view1_copy] == 10); // view1_copy views same node as view1

See alsotf::TaskView::hash_value() for obtaining the hash value directly.

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