graph_task.h File Reference

DAG-based task graph with condition branching, cycle detection, and DOT export. More...

#include <functional>
#include <memory>
#include <string>
#include <unordered_set>
#include <utility>
#include <vector>
#include "./macros.h"
#include "./traits.h"

Include dependency graph for graph_task.h:

Go to the source code of this file.

Classes
class	vlink::GraphTask
	Node in a directed acyclic task graph supporting condition branching and parallel execution. More...

Namespaces
namespace	vlink

Typedefs
using	vlink::GraphTaskPtr = std::shared_ptr<GraphTask>

Detailed Description

DAG-based task graph with condition branching, cycle detection, and DOT export.

GraphTask implements a directed acyclic graph (DAG) of work units. Tasks define their dependencies by calling precede() (this task must finish before the target) or succeed() (the target must finish before this task). The entire graph is then submitted to any MessageLoop, MultiLoop or ThreadPool via execute().

Task types:

Factory	Callback signature	Use case
create(callback)	void()	Regular work task
create_condition(callback)	int()	Branch selector (returns branch id)

Condition task: A condition task returns an integer selecting which successor sub-graph to activate. All other successors are skipped. This enables if/switch style DAG branching.

Execution policies:

Policy	Behaviour
kPolicyOnce	Task runs exactly once per execute() call (default)
kPolicyMultiple	Task may run multiple times in one execute() pass
kPolicyWaitAll	Task waits for all predecessors before running (default DAG rule)

Operator syntax for building graphs:

auto A = vlink::GraphTask::create("A", []{ step_a(); });
auto B = vlink::GraphTask::create("B", []{ step_b(); });
auto C = vlink::GraphTask::create("C", []{ step_c(); });
 
A-- > B-- > C;  // A depends on B, B depends on C (execution order: C, B, A)

Note

• execute() traverses the reachable sub-graph and dispatches all ready tasks to the engine.
• has_cycle() detects cycles using DFS; cycles cause undefined behaviour at runtime.
• export_to_dot() produces a Graphviz DOT string for visualisation.

Example

vlink::MultiLoop engine(4);
engine.async_run();
 
auto load  = vlink::GraphTask::create("load",  [] { load_data(); });
auto proc  = vlink::GraphTask::create("proc",  [] { process();   });
auto save  = vlink::GraphTask::create("save",  [] { save_data(); });
 
// A-- > B calls A->succeed(B), meaning B must complete before A.
// So save-- > proc-- > load produces execution order: load, proc, save.
save-- > proc-- > load;
 
assert(!save->has_cycle());
save->execute(&engine);