User Guide

Intel® VTune™ Profiler User Guide

ID 766319
Date 11/07/2023
Public

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Document Table of Contents

Task API

A task is a logical unit of work performed by a particular thread. Tasks can nest; thus, tasks typically correspond to functions, scopes, or a case block in a switch statement. You can use the Task API to assign tasks to threads.

Task API is a per-thread function that works in resumed state. This function does not work in paused state.

The Task API does not enable a thread to suspend the current task and switch to a different task (task switching), or move a task to a different thread (task stealing).

A task instance represents a piece of work performed by a particular thread for a period of time. The task is defined by the bracketing of __itt_task_begin() and __itt_task_end() on the same thread.

NOTE:

To be able to see user tasks in your results, enable the Analyze user tasks checkbox in analysis settings.

Task API Functions

Create a task instance on a thread. This becomes the current task instance for that thread. A call to __itt_task_end() on the same thread ends the current task instance.

void __itt_task_begin (const __itt_domain *domain,__itt_id taskid, __itt_id parentid, __itt_string_handle *name)

Trace the end of the current task.

void __itt_task_end (const __itt_domain *domain)

ITTAPI__itt_task_* Function Parameters

The following table defines the parameters used in the Task API primitives.

Type

Parameter

Description

[in]

__itt_domain

The domain of the task.

[in]

__itt_id taskid

This is a reserved parameter.

[in]

__itt_id parentid

This is a reserved parameter.

[in]

__itt_string_handle

The task string handle.

Enable Task APIs

The following steps are required to begin using task APIs:

  1. Include ittnotify.h header.
  2. Create domain and string handles for your tasks.
  3. Insert task begin and task end marks in your code.
  4. Link to libittnotify.lib (Windows*) or libittnotify.a (Linux*).
  5. Enable the Analyze user tasks, events, and counters option before profiling. For more information, see Task Analysis topic.

Usage Example

The following code snippet creates a domain and a couple of tasks at global scope.

#include "ittnotify.h" void do_foo(double seconds); __itt_domain* domain = __itt_domain_create("MyTraces.MyDomain"); __itt_string_handle* shMyTask = __itt_string_handle_create("My Task"); __itt_string_handle* shMySubtask = __itt_string_handle_create("My SubTask"); void BeginFrame() { __itt_task_begin(domain, __itt_null, __itt_null, shMyTask); do_foo(1); } void DoWork() { __itt_task_begin(domain, __itt_null, __itt_null, shMySubtask); do_foo(1); __itt_task_end(domain); } void EndFrame() { do_foo(1); __itt_task_end(domain); } int main() { BeginFrame(); DoWork(); EndFrame(); return 0; } #ifdef _WIN32 #include <ctime> void do_foo(double seconds) { clock_t goal = (clock_t)((double)clock() + seconds * CLOCKS_PER_SEC); while (goal > clock()); } #else #include <time.h> #define NSEC 1000000000 #define TYPE long void do_foo(double sec) { struct timespec start_time; struct timespec current_time; clock_gettime(CLOCK_REALTIME, &start_time); while(1) { clock_gettime(CLOCK_REALTIME, &current_time); TYPE cur_nsec=(long)((current_time.tv_sec-start_time.tv_sec-sec)*NSEC + current_time.tv_nsec - start_time.tv_nsec); if(cur_nsec>=0) break; } } #endif