iframe-proxy | Sunbelt Computer Software

History

1441 lines (1415 loc) · 130 KB

Raw

100

101

102

103

104

105

106

107

108

109

110

111

112

113

114

115

116

117

118

119

120

121

122

123

124

125

126

127

128

129

130

131

132

133

134

135

136

137

138

139

140

141

142

143

144

145

146

147

148

149

150

151

152

153

154

155

156

157

158

159

160

161

162

163

164

165

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

181

182

183

184

185

186

187

188

189

190

191

192

193

194

195

196

197

198

199

200

201

202

203

204

205

206

207

208

209

210

211

212

213

214

215

216

217

218

219

220

221

222

223

224

225

226

227

228

229

230

231

232

233

234

235

236

237

238

239

240

241

242

243

244

245

246

247

248

249

250

251

252

253

254

255

256

257

258

259

260

261

262

263

264

265

266

267

268

269

270

271

272

273

274

275

276

277

278

279

280

281

282

283

284

285

286

287

288

289

290

291

292

293

294

295

296

297

298

299

300

301

302

303

304

305

306

307

308

309

310

311

312

313

314

315

316

317

318

319

320

321

322

323

324

325

326

327

328

329

330

331

332

333

334

335

336

337

338

339

340

341

342

343

344

345

346

347

348

349

350

351

352

353

354

355

356

357

358

359

360

361

362

363

364

365

366

367

368

369

370

371

372

373

374

375

376

377

378

379

380

381

382

383

384

385

386

387

388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

407

408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

423

424

425

426

427

428

429

430

431

432

433

434

435

436

437

438

439

440

441

442

443

444

445

446

447

448

449

450

451

452

453

454

455

456

457

458

459

460

461

462

463

464

465

466

467

468

469

470

471

472

473

474

475

476

477

478

479

480

481

482

483

484

485

486

487

488

489

490

491

492

493

494

495

496

497

498

499

500

501

502

503

504

505

506

507

508

509

510

511

512

513

514

515

516

517

518

519

520

521

522

523

524

525

526

527

528

529

530

531

532

533

534

535

536

537

538

539

540

541

542

543

544

545

546

547

548

549

550

551

552

553

554

555

556

557

558

559

560

561

562

563

564

565

566

567

568

569

570

571

572

573

574

575

576

577

578

579

580

581

582

583

584

585

586

587

588

589

590

591

592

593

594

595

596

597

598

599

600

601

602

603

604

605

606

607

608

609

610

611

612

613

614

615

616

617

618

619

620

621

622

623

624

625

626

627

628

629

630

631

632

633

634

635

636

637

638

639

640

641

642

643

644

645

646

647

648

649

650

651

652

653

654

655

656

657

658

659

660

661

662

663

664

665

666

667

668

669

670

671

672

673

674

675

676

677

678

679

680

681

682

683

684

685

686

687

688

689

690

691

692

693

694

695

696

697

698

699

700

701

702

703

704

705

706

707

708

709

710

711

712

713

714

715

716

717

718

719

720

721

722

723

724

725

726

727

728

729

730

731

732

733

734

735

736

737

738

739

740

741

742

743

744

745

746

747

748

749

750

751

752

753

754

755

756

757

758

759

760

761

762

763

764

765

766

767

768

769

770

771

772

773

774

775

776

777

778

779

780

781

782

783

784

785

786

787

788

789

790

791

792

793

794

795

796

797

798

799

800

801

802

803

804

805

806

807

808

809

810

811

812

813

814

815

816

817

818

819

820

821

822

823

824

825

826

827

828

829

830

831

832

833

834

835

836

837

838

839

840

841

842

843

844

845

846

847

848

849

850

851

852

853

854

855

856

857

858

859

860

861

862

863

864

865

866

867

868

869

870

871

872

873

874

875

876

877

878

879

880

881

882

883

884

885

886

887

888

889

890

891

892

893

894

895

896

897

898

899

900

901

902

903

904

905

906

907

908

909

910

911

912

913

914

915

916

917

918

919

920

921

922

923

924

925

926

927

928

929

930

931

932

933

934

935

936

937

938

939

940

941

942

943

944

945

946

947

948

949

950

951

952

953

954

955

956

957

958

959

960

961

962

963

964

965

966

967

968

969

970

971

972

973

974

975

976

977

978

979

980

981

982

983

984

985

986

987

988

989

990

991

992

993

994

995

996

997

998

999

1000

<!DOCTYPE html>

<head>

<title>Cookbook » Conditional Tasking | Taskflow QuickStart</title>

</head>

<body>

<a href="https://taskflow.github.io"><img src="taskflow_logo.png" alt="" />Taskflow</a> | <a href="index.html" class="m-thin">QuickStart</a>

</svg></a>

</div>

<li><a href="pages.html">Handbook</a></li>

<li><a href="namespaces.html">Namespaces</a></li>

</ol>

<li><a href="annotated.html">Classes</a></li>

<li><a href="files.html">Files</a></li>

</svg></a></li>

</ol>

</div>

</nav></header>

<h1>

<a href="Cookbook.html">Cookbook</a> »

Conditional Tasking

</h1>

<h3>Contents</h3>

<ul>

<li><a href="#CreateAConditionTask">Create a Condition Task</a></li>

<li>

<a href="#TaskSchedulingPolicy">Understand our Task-level Scheduling</a>

<ul>

<li><a href="#TaskLevelSchedulingExample">Example</a></li>

</ul>

</li>

<li><a href="#AvoidCommonPitfalls">Avoid Common Pitfalls</a></li>

<li>

<a href="#ImplementControlFlowGraphs">Implement Control-flow Graphs</a>

<ul>

<li><a href="#ImplementIfElseControlFlow">Implement If-Else Control Flow</a></li>

<li><a href="#ImplementSwitchControlFlow">Implement Switch Control Flow</a></li>

<li><a href="#ImplementDoWhileLoopControlFlow">Implement Do-While-Loop Control Flow</a></li>

<li><a href="#ImplementWhileLoopControlFlow">Implement While-Loop Control Flow</a></li>

</ul>

</li>

<li><a href="#CreateAMultiConditionTask">Create a Multi-condition Task</a></li>

</ul>

</nav>

Parallel workloads often require making control-flow decisions across dependent tasks. Taskflow supports an very efficient interface of conditional tasking for users to implement general control flow such as dynamic flow, cycles, and conditionals that are otherwise difficult to do with existing frameworks.<section id="CreateAConditionTask"><h2><a href="#CreateAConditionTask">Create a Condition Task</a></h2>A condition task evaluates a set of instructions and returns an integer index of the next successor task to execute. The index is defined with respect to the order of its successor construction. The following example creates an if-else block using a single condition task.<pre class="m-code"> 1: tf::Taskflow taskflow;

2:

3: auto [init, cond, yes, no] = taskflow.emplace(

4: [] () { },

5: [] () { return 0; },

6: [] () { std::cout << "yes\n"; },

7: [] () { std::cout << "no\n"; }

8: );

9:

10: cond.succeed(init)

11: .precede(yes, no); // executes yes if cond returns 0

12: // executes no if cond returns 1</pre><div class="m-graph"><svg style="width: 25.600rem; height: 9.800rem;" viewBox="0.00 0.00 256.17 98.00">

<title>Taskflow</title>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</svg>

</div>Line 5 creates a condition task <code>cond</code> and line 11 creates two dependencies from <code>cond</code> to two other tasks, <code>yes</code> and <code>no</code>. With this order, when <code>cond</code> returns 0, the execution moves on to task <code>yes</code>. When <code>cond</code> returns 1, the execution moves on to task <code>no</code>.<aside class="m-note m-warning"><h4>Attention</h4>It is your responsibility to ensure the return of a condition task goes to a correct successor task. If the return falls beyond the range of the successors, the executor will not schedule any tasks.</aside>Condition task can go cyclic to describe iterative control flow. The example below implements a simple yet commonly used feedback loop through a condition task (line 7-10) that returns a random binary value. If the return value from <code>cond</code> is <code>0</code>, it loops back to itself, or otherwise to <code>stop</code>.<pre class="m-code"> 1: tf::Taskflow taskflow;

2:

3: tf::Task init = taskflow.emplace([](){}).name("init");

4: tf::Task stop = taskflow.emplace([](){}).name("stop");

5:

6: // creates a condition task that returns 0 or 1

7: tf::Task cond = taskflow.emplace([](){

8: std::cout << "flipping a coin\n";

9: return std::rand() % 2;

10: }).name("cond");

11:

12: // creates a feedback loop {0: cond, 1: stop}

13: init.precede(cond);

14: cond.precede(cond, stop); // returns 0 to 'cond' or 1 to 'stop'

15:

16: executor.run(taskflow).wait();</pre><div class="m-graph"><svg style="width: 25.600rem; height: 7.300rem;" viewBox="0.00 0.00 256.17 73.25">

<title>Taskflow</title>

</g>

</g>

</g>

</g>

</g>

</g>

</svg>

</div>A taskflow of complex control flow often just takes a few lines of code to implement, and different control flow blocks may run in parallel. The code below creates another taskflow with three condition tasks.<pre class="m-code">tf::Taskflow taskflow;

tf::Task A = taskflow.emplace([](){}).name("A");

tf::Task B = taskflow.emplace([](){}).name("B");

tf::Task C = taskflow.emplace([](){}).name("C");

tf::Task D = taskflow.emplace([](){}).name("D");

tf::Task E = taskflow.emplace([](){}).name("E");

tf::Task F = taskflow.emplace([](){}).name("F");

tf::Task G = taskflow.emplace([](){}).name("G");

tf::Task H = taskflow.emplace([](){}).name("H");

tf::Task I = taskflow.emplace([](){}).name("I");

tf::Task K = taskflow.emplace([](){}).name("K");

tf::Task L = taskflow.emplace([](){}).name("L");

tf::Task M = taskflow.emplace([](){}).name("M");

tf::Task cond_1 = taskflow.emplace([](){ return std::rand()%2; }).name("cond_1");

tf::Task cond_2 = taskflow.emplace([](){ return std::rand()%2; }).name("cond_2");

tf::Task cond_3 = taskflow.emplace([](){ return std::rand()%2; }).name("cond_3");

A.precede(B, F);

B.precede(C);

C.precede(D);

D.precede(cond_1);

E.precede(K);

F.precede(cond_2);

H.precede(I);

I.precede(cond_3);

L.precede(M);

cond_1.precede(B, E); // return 0 to 'B' or 1 to 'E'

cond_2.precede(G, H); // return 0 to 'G' or 1 to 'H'

cond_3.precede(cond_3, L); // return 0 to 'cond_3' or 1 to 'L'

taskflow.dump(std::cout);</pre>The above code creates three condition tasks: (1) a condition task <code>cond_1</code> that loops back to <code>B</code> on returning <code>0</code>, or proceeds to <code>E</code> on returning <code>1</code>, (2) a condition task <code>cond_2</code> that goes to <code>G</code> on returning <code>0</code>, or <code>H</code> on returning <code>1</code>, (3) a condition task <code>cond_3</code> that loops back to itself on returning <code>0</code>, or proceeds to <code>L</code> on returning <code>1</code><div class="m-graph"><svg style="width: 78.800rem; height: 19.200rem;" viewBox="0.00 0.00 788.23 192.00">

<title>Taskflow</title>

<title>p0x7fecbdc02830</title>

</g>

<title>p0x7fecbdc02940</title>

</g>

<title>p0x7fecbdc02830->p0x7fecbdc02940</title>

</g>

<title>p0x7fecbdc02d80</title>

</g>

<title>p0x7fecbdc02830->p0x7fecbdc02d80</title>

</g>

<title>p0x7fecbdc02a50</title>

</g>

<title>p0x7fecbdc02940->p0x7fecbdc02a50</title>

</g>

<title>p0x7fecbdc03600</title>

</g>

<title>p0x7fecbdc02d80->p0x7fecbdc03600</title>

</g>

<title>p0x7fecbdc02b60</title>

</g>

<title>p0x7fecbdc02a50->p0x7fecbdc02b60</title>

</g>

<title>p0x7fecbdc034f0</title>

</g>

<title>p0x7fecbdc02b60->p0x7fecbdc034f0</title>

</g>

<title>p0x7fecbdc034f0->p0x7fecbdc02940</title>

</g>

<title>p0x7fecbdc02c70</title>

</g>

<title>p0x7fecbdc034f0->p0x7fecbdc02c70</title>

</g>

<title>p0x7fecbdc031c0</title>

</g>

<title>p0x7fecbdc02c70->p0x7fecbdc031c0</title>

</g>

<title>p0x7fecbdc02e90</title>

</g>

<title>p0x7fecbdc03600->p0x7fecbdc02e90</title>

</g>

<title>p0x7fecbdc02fa0</title>

</g>

<title>p0x7fecbdc03600->p0x7fecbdc02fa0</title>

</g>

<title>p0x7fecbdc030b0</title>

</g>

<title>p0x7fecbdc02fa0->p0x7fecbdc030b0</title>

</g>

<title>p0x7fecbdc03710</title>

</g>

<title>p0x7fecbdc030b0->p0x7fecbdc03710</title>

</g>

<title>p0x7fecbdc03710->p0x7fecbdc03710</title>

</g>

<title>p0x7fecbdc032d0</title>

</g>

<title>p0x7fecbdc03710->p0x7fecbdc032d0</title>

</g>

<title>p0x7fecbdc033e0</title>

</g>

<title>p0x7fecbdc032d0->p0x7fecbdc033e0</title>

</g>

</svg>

</div>You can use condition tasks to create cycles as long as the graph does not introduce task race during execution. However, cycles are not allowed in non-condition tasks.<aside class="m-note m-info"><h4>Note</h4>Conditional tasking lets you make in-task control-flow decisions to enable end-to-end parallelism, instead of resorting to client-side partition or synchronizing your task graph at the decision points of control flow.</aside></section><section id="TaskSchedulingPolicy"><h2><a href="#TaskSchedulingPolicy">Understand our Task-level Scheduling</a></h2>In order to understand how an executor schedules condition tasks, we define two dependency types, strong dependency and weak dependency. A strong dependency is a preceding link from a non-condition task to another task. A weak dependency is a preceding link from a condition task to another task. The number of dependents of a task is the sum of strong dependency and weak dependency. The table below lists the strong dependency and weak dependency numbers of each task in the previous example.<table class="m-table"><thead><tr><th>task</th><th>strong dependency</th><th>weak dependency</th><th>dependents</th></tr></thead><tbody><tr><td>A</td><td>0</td><td>0</td><td>0</td></tr><tr><td>B</td><td>1</td><td>1</td><td>2</td></tr><tr><td>C</td><td>1</td><td>0</td><td>1</td></tr><tr><td>D</td><td>1</td><td>0</td><td>1</td></tr><tr><td>E</td><td>0</td><td>1</td><td>1</td></tr><tr><td>F</td><td>1</td><td>0</td><td>1</td></tr><tr><td>G</td><td>0</td><td>1</td><td>1</td></tr><tr><td>H</td><td>0</td><td>1</td><td>1</td></tr><tr><td>I</td><td>1</td><td>0</td><td>1</td></tr><tr><td>K</td><td>1</td><td>0</td><td>1</td></tr><tr><td>L</td><td>0</td><td>1</td><td>1</td></tr><tr><td>M</td><td>1</td><td>0</td><td>1</td></tr><tr><td>cond_1</td><td>1</td><td>0</td><td>1</td></tr><tr><td>cond_2</td><td>1</td><td>0</td><td>1</td></tr><tr><td>cond_3</td><td>1</td><td>1</td><td>2</td></tr></tbody></table>You can query the number of strong dependents, the number of weak dependents, and the number of dependents of a task.<pre class="m-code">1: tf::Taskflow taskflow;

2:

3: tf::Task task = taskflow.emplace([](){});

4:

5: // ... add more tasks and preceding links

6:

7: std::cout << task.num_dependents() << '\n';

8: std::cout << task.num_strong_dependents() << '\n';

9: std::cout << task.num_weak_dependents() << '\n';</pre>When you submit a task to an executor, the scheduler starts with tasks of zero dependents (both zero strong and weak dependencies) and continues to execute successive tasks whenever their strong dependencies are met. However, the scheduler skips this rule when executing a condition task and jumps directly to its successors indexed by the return value.<div class="m-graph"><svg style="width: 55.800rem; height: 34.600rem;" viewBox="0.00 0.00 558.12 346.25">

<title>atask</title>

</g>

<text text-anchor="middle" x="337.89" y="-243.38" font-family="Helvetica,sans-Serif" font-size="10.00">is T a condition task?</text>

</g>

<title>atask->cond</title>

</g>

<title>invokeN</title>

<text text-anchor="middle" x="289.89" y="-160.12" font-family="Helvetica,sans-Serif" font-size="10.00">invoke(T)</text>

</g>

<title>cond->invokeN</title>

</g>

<title>invokeY</title>

<text text-anchor="middle" x="432.89" y="-160.12" font-family="Helvetica,sans-Serif" font-size="10.00">R = invoke(T)</text>

</g>

<title>cond->invokeY</title>

</g>

<title>decrement</title>

<text text-anchor="middle" x="171.89" y="-87.12" font-family="Helvetica,sans-Serif" font-size="10.00">decrement strong dependencies of each successor of T by one</text>

</g>

<title>invokeN->decrement</title>

</g>

<title>enqueueR</title>

<text text-anchor="middle" x="455.89" y="-87.12" font-family="Helvetica,sans-Serif" font-size="10.00">enqueue the R-th successor of T</text>

</g>

<title>invokeY->enqueueR</title>

</g>

<title>enqueueS</title>

<text text-anchor="middle" x="171.89" y="-14.12" font-family="Helvetica,sans-Serif" font-size="10.00">enqueue successors of zero strong dependencies</text>

</g>

<title>decrement->enqueueS</title>

</g>

</svg>

</div>Each task has an atomic join counter to keep track of strong dependents that are met at runtime. When a task completes, the join counter is restored to the task's strong dependency number in the graph, such that the subsequent execution can reuse the counter again.<section id="TaskLevelSchedulingExample"><h3><a href="#TaskLevelSchedulingExample">Example</a></h3>Let's take a look at an example to understand how task-level scheduling works. Suppose we have the following taskflow of one condition task <code>cond</code> that forms a loop to itself on returning <code>0</code> and moves on to <code>stop</code> on returning <code>1</code>:<div class="m-graph"><svg style="width: 25.600rem; height: 7.300rem;" viewBox="0.00 0.00 256.17 73.25">

<title>Taskflow</title>

</g>

</g>

</g>

</g>

</g>

</g>

</svg>

</div>The scheduler starts with <code>init</code> task because it has no dependencies (both strong and weak dependencies). Then, the scheduler moves on to the condition task <code>cond</code>. If <code>cond</code> returns <code>0</code>, the scheduler enqueues <code>cond</code> and runs it again. If <code>cond</code> returns <code>1</code>, the scheduler enqueues <code>stop</code> and then moves on.</section></section><section id="AvoidCommonPitfalls"><h2><a href="#AvoidCommonPitfalls">Avoid Common Pitfalls</a></h2>Condition tasks are handy in creasing dynamic and cyclic control flows, but they are also easy to make mistakes. It is your responsibility to ensure a taskflow is properly conditioned. Top things to avoid include no source tasks to start with and task race. The figure below shows common pitfalls and their remedies.<div class="m-graph"><svg style="width: 91.000rem; height: 26.200rem;" viewBox="0.00 0.00 910.00 261.75">

<title>Taskflow</title>

<title>cluster_error1</title>

<text text-anchor="middle" x="79" y="-232.25" font-family="Helvetica,sans-Serif" font-size="10.00">error1: no source tasks</text>

</g>

<title>cluster_fix1</title>

<text text-anchor="middle" x="229" y="-232.25" font-family="Helvetica,sans-Serif" font-size="10.00">fix1: adds a source</text>

</g>

<title>cluster_error2</title>

<text text-anchor="middle" x="379" y="-232.25" font-family="Helvetica,sans-Serif" font-size="10.00">error2: race on D</text>

</g>

<title>cluster_fix2</title>

<text text-anchor="middle" x="565" y="-232.25" font-family="Helvetica,sans-Serif" font-size="10.00">fix2: adds an auxiliary task</text>

</g>

<title>cluster_risky</title>

<text text-anchor="middle" x="787" y="-232.25" font-family="Helvetica,sans-Serif" font-size="10.00">risky: X might be raced</text>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</svg>

</div>In the <code>error1</code> scenario, there is no source task for the scheduler to start with, and the simplest fix is to add a task <code>S</code> that has no dependents. In the <code>error2</code> scenario, <code>D</code> might be scheduled twice by <code>E</code> through the strong dependency and <code>C</code> through the weak dependency (on returning <code>1</code>). To fix this problem, you can add an auxiliary task <code>D-aux</code> to break the mixed use of strong dependency and weak dependency. In the risky scenario, task <code>X</code> may be raced by <code>M</code> and <code>P</code> if <code>M</code> returns <code>0</code> and P returns <code>1</code>.<aside class="m-note m-warning"><h4>Attention</h4>It is your responsibility to ensure a written taskflow graph is properly conditioned. We suggest that you <a href="ConditionalTasking.html#TaskSchedulingPolicy" class="m-doc">Understand our Task-level Scheduling</a> and infer if task race exists in the execution of your graph.</aside></section><section id="ImplementControlFlowGraphs"><h2><a href="#ImplementControlFlowGraphs">Implement Control-flow Graphs</a></h2><section id="ImplementIfElseControlFlow"><h3><a href="#ImplementIfElseControlFlow">Implement If-Else Control Flow</a></h3>You can use conditional tasking to implement if-else control flow. The following example creates a nested if-else control flow diagram that executes three condition tasks to check the range of <code>i</code>.<pre class="m-code">tf::Taskflow taskflow;

int i;

// create three condition tasks for nested control flow

auto initi = taskflow.emplace([&](){ i=3; });

auto cond1 = taskflow.emplace([&](){ return i>1 ? 1 : 0; });

auto cond2 = taskflow.emplace([&](){ return i>2 ? 1 : 0; });

auto cond3 = taskflow.emplace([&](){ return i>3 ? 1 : 0; });

auto equl1 = taskflow.emplace([&](){ std::cout << "i=1\n"; });

auto equl2 = taskflow.emplace([&](){ std::cout << "i=2\n"; });

auto equl3 = taskflow.emplace([&](){ std::cout << "i=3\n"; });

auto grtr3 = taskflow.emplace([&](){ std::cout << "i>3\n"; });

initi.precede(cond1);

cond1.precede(equl1, cond2); // goes to cond2 if i>1

cond2.precede(equl2, cond3); // goes to cond3 if i>2

cond3.precede(equl3, grtr3); // goes to grtr3 if i>3</pre><div class="m-graph"><svg style="width: 75.600rem; height: 15.200rem;" viewBox="0.00 0.00 756.23 152.00">

<title>Taskflow</title>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</svg>

</div></section><section id="ImplementSwitchControlFlow"><h3><a href="#ImplementSwitchControlFlow">Implement Switch Control Flow</a></h3>You can use conditional tasking to implement switch control flow. The following example creates a switch control flow diagram that executes one of the three cases at random using four condition tasks.<pre class="m-code">tf::Taskflow taskflow;

auto [source, swcond, case1, case2, case3, target] = taskflow.emplace(

[](){ std::cout << "switch\n"; return rand()%3; },

[](){ std::cout << "case 1\n"; return 0; },

[](){ std::cout << "case 2\n"; return 0; },

[](){ std::cout << "case 3\n"; return 0; },

);

source.precede(swcond);

swcond.precede(case1, case2, case3);

target.succeed(case1, case2, case3);</pre><div class="m-graph"><svg style="width: 38.600rem; height: 15.200rem;" viewBox="0.00 0.00 385.70 152.00">

<title>Taskflow</title>

<text text-anchor="middle" x="27" y="-68.12" font-family="Helvetica,sans-Serif" font-size="10.00">source</text>

</g>

<text text-anchor="middle" x="128.24" y="-68.12" font-family="Helvetica,sans-Serif" font-size="10.00">switch</text>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

<text text-anchor="middle" x="350.7" y="-68.12" font-family="Helvetica,sans-Serif" font-size="10.00">target</text>

</g>

</g>

</g>

</g>

</svg>

</div>Assuming <code>swcond</code> returns 1, the program outputs:<pre class="m-console">source

switch

case 2

target</pre>Keep in mind, both switch and case tasks must be described as condition tasks. The following implementation is a common mistake in which case tasks are not described as condition tasks.<pre class="m-code">// wrong implementation of switch control flow using only one condition task

tf::Taskflow taskflow;

[](){ std::cout << "target\n"; } // target has three strong dependencies

);

source.precede(swcond);

target.succeed(case1, case2, case3);</pre><div class="m-graph"><svg style="width: 36.000rem; height: 15.200rem;" viewBox="0.00 0.00 359.72 152.00">

<title>Taskflow</title>

<text text-anchor="middle" x="27" y="-68.12" font-family="Helvetica,sans-Serif" font-size="10.00">source</text>

</g>

<text text-anchor="middle" x="128.24" y="-68.12" font-family="Helvetica,sans-Serif" font-size="10.00">switch</text>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

</g>

<text text-anchor="middle" x="324.72" y="-68.12" font-family="Helvetica,sans-Serif" font-size="10.00">target</text>

</g>

View remainder of file in raw view

Sunbelt Computer Software

PL/B Language Development and Support

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Sunbelt Computer Software

PL/B Language Development and Support

FilesExpand file tree

ConditionalTasking.html

Latest commit

History

ConditionalTasking.html

File metadata and controls