Intel® VTune™ Profiler User Guide

User Guide

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.
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

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.