Event API

The event API is used to observe when demarcated events occur in your application, or to identify how long it takes to execute demarcated regions of code. Set annotations in the application to demarcate areas where events of interest occur. After running analysis, you can see the events marked in the Timeline pane.

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

Note

  • On Windows* OS platforms you can define Unicode to use a wide character version of APIs that pass strings. However, these strings are internally converted to ASCII strings.

  • On Linux* OS platforms only a single variant of the API exists.

Use This Primitive

To Do This

__itt_event __itt_event_create(const __itt_char *name, int namelen );

Create an event type with the specified name and length. This API returns a handle to the event type that should be passed into the following event start and event end APIs as a parameter. The namelen parameter refers to the name length in number of characters, not the number of bytes.

int __itt_event_start( __itt_event event );

 

Call this API with your previously created event type handle to register an instance of the event. Event start appears in the Timeline pane display as a tick mark.

int __itt_event_end( __itt_event event );

Call this API following a call to __itt_event_start() to show the event as a tick mark with a duration line from start to end. If this API is not called, this event appears in the Timeline pane as a single tick mark.

Guidelines for Event API Usage

  • An __itt_event_end() is always matched with the nearest preceding __itt_event_start(). Otherwise, the __itt_event_end() call is matched with the nearest unmatched __itt_event_start() preceding it. Any intervening events are nested.

  • You can nest user events of the same or different type within each other. In the case of nested events, the time is considered to have been spent only in the most deeply nested user event region.

  • You can overlap different ITT API events. In the case of overlapping events the time is considered to have been spent only in the event region with the later __itt_event_start(). Unmatched __itt_event_end() calls are ignored.

Note

To see events and user tasks in your results, select the Analyze user tasks checkbox in the analysis settings.

Usage Example: Creating and Marking Single Events

The __itt_event_create API returns a new event handle that you can subsequently use to mark user events with the __itt_event_start API. In this example, two event type handles are created and used to set the start points for tracking two different types of events.

#include "ittnotify.h"

__itt_event mark_event = __itt_event_create( "User Mark", 9 );
__itt_event frame_event = __itt_event_create( "Frame Completed", 15 );
...
__itt_event_start( mark_event );
...
for( int f ; f<number_of_frames ; f++ ) {
  ...
  __itt_event_start( markframe_event );
}

Usage Example: Creating and Marking Event Regions

The __itt_event_start API can be followed by an __itt_event_end API to define an event region, as in the following example:

#include "ittnotify.h"

__itt_event render_event = __itt_event_create( "Rendering Phase", 15 );
...
for( int f ; f<number_of_frames ; f++ ) {
  ...
  do_stuff_for_frame();
  ...
  __itt_event_start( render_event );
  ...
  do_rendering_for_frame();
  ...
  __itt_event_end( render_event );
  ...
}

For more complete information about compiler optimizations, see our Optimization Notice.
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