Event

A representation of events used in stream synchronization and timing. More...

Typedefs
typedef struct VPIEventImpl *	VPIEvent
	A handle to an event.

Functions
VPIStatus	vpiEventCreate (uint32_t flags, VPIEvent *event)
	Create an event instance with the specified flags. More...
void	vpiEventDestroy (VPIEvent event)
	Destroy an event instance as well as all resources it owns. More...
VPIStatus	vpiEventRecord (VPIEvent event, VPIStream stream)
	Captures in the event the contents of the stream command queue at the time of this call. More...
VPIStatus	vpiEventSync (VPIEvent event)
	Blocks the calling thread until the event is signaled. More...
VPIStatus	vpiEventQuery (VPIEvent event, VPIEventState *state)
	Queries the status of all work currently captured by the event. More...
VPIStatus	vpiEventElapsedTimeMillis (VPIEvent start, VPIEvent end, float *msec)
	Computes the elapsed time in (msec) between two completed events. More...
VPIStatus	vpiEventGetFlags (VPIEvent event, uint32_t *flags)
	Returns the event flags passed during event creation. More...

Event-specific flags.
#define	VPI_EVENT_DISABLE_TIMESTAMP   (1 << 18)
	disable time-stamping of event signaling for better performance.

Detailed Description

A representation of events used in stream synchronization and timing.

Each compute function in the API is executed asynchronously with respect to the calling thread, i.e., returns immediately without waiting for the completion. There are two ways of synchronizing with the backend. One is to wait until all the commands in the VPIStream queue are finished, with the vpiStreamSync call. This approach, while simple, doesn't allow for fine-grained ("wait for until function X is completed") or inter-device ("before running function A in device B, wait until function C in device D finishes") synchronization. That's where VPIEvent objects come in. Conceptually, they correspond to binary semaphores and are designed to closely mimic events in CUDA API:

• Users can capture all commands submitted to a VPIStream instance in an event instance (see vpiEventRecord). The event is considered completed when all captured commands have been processed and removed from VPIStream command queue.
• Inter-device synchronization is possible with vpiStreamWaitEvent call that pushes a command to VPIStream queue that blocks processing of future queued commands until given event is completed.
• Host threads can query the event's state with vpiEventQuery
• Host threads can block until event is completed with vpiEventSync.
• Events can be time-stamped when completed.
• Users can compute time-stamp difference between completed events in the same device as well as between different devices. This implies that internally, the API has to have a notion of unified time source.

Function Documentation

vpiEventCreate()

VPIStatus vpiEventCreate	(	uint32_t	flags,
		VPIEvent *	event
	)

#include <vpi/Event.h>

Create an event instance with the specified flags.

Parameters

[in]	flags	Event flags. Here it can be specified in what backends the image can be used by or-ing together VPIBackend flags. Set flags to 0 to enable it in all backends supported by the active VPI context. Additional flags can also be specified.
[out]	event	Pointer to memory that will receive the created event handle.

Returns

an error code on failure else VPI_SUCCESS.

vpiEventDestroy()

void vpiEventDestroy

(

VPIEvent

event

)

#include <vpi/Event.h>

Destroy an event instance as well as all resources it owns.

Parameters

[in]

event

event handle

vpiEventElapsedTimeMillis()

VPIStatus vpiEventElapsedTimeMillis	(	VPIEvent	start,
		VPIEvent	end,
		float *	msec
	)

#include <vpi/Event.h>

Computes the elapsed time in (msec) between two completed events.

If one or both are not completed at the time of the call, VPI_ERROR_NOT_READY is returned, otherwise VPI_SUCCESS.

Parameters

[in]	start	an event handle marking the start of the time interval
[in]	end	an event handle marking the end of the time interval
[out]	msec	a pointer to a variable which will be set to the time difference between the events

Returns

an error code on failure, VPI_ERROR_NOT_READY if at least one event is not ready, else VPI_SUCCESS

vpiEventGetFlags()

VPIStatus vpiEventGetFlags	(	VPIEvent	event,
		uint32_t *	flags
	)

#include <vpi/Event.h>

Returns the event flags passed during event creation.

Parameters

[in]	event	An event handle.
[out]	flags	Pointer to memory that will hold the event flags. It can't be NULL.

Returns

An error code on failure, or else VPI_SUCCESS.

vpiEventQuery()

VPIStatus vpiEventQuery	(	VPIEvent	event,
		VPIEventState *	state
	)

#include <vpi/Event.h>

Queries the status of all work currently captured by the event.

If all tasks are finished, VPI_SUCCESS is returned, otherwise VPI_ERROR_NOT_READY.

Parameters

[in]	event	An event handle.
[out]	state	Pointer to memory that will receive the states of the event. State is only valid when the return status is VPI_SUCCESS.

Returns

an error code on failure else VPI_SUCCESS

vpiEventRecord()

VPIStatus vpiEventRecord	(	VPIEvent	event,
		VPIStream	stream
	)

#include <vpi/Event.h>

Captures in the event the contents of the stream command queue at the time of this call.

When all tasks recorded are finished, the event will be signaled and calls that are waiting for it will be unblocked.

This function can be called multiple times on the same event, however existing vpiEventSync / vpiStreamWaitEvent calls are not affected by later calls to vpiEventRecord. This means they will wait for the event completion of the command queue tasks described by the event at the time of the initial vpiEventSync / vpiStreamWaitEvent call.

The operation will implicitly flush the stream.

Parameters

[in]	event	An event handle
[in]	stream	A stream handle whose command queue with tasks yet to be executed will be recorded in the event.

Returns

an error code on failure else VPI_SUCCESS.

vpiEventSync()

VPIStatus vpiEventSync

(

VPIEvent

event

)

#include <vpi/Event.h>

Blocks the calling thread until the event is signaled.

The event is considered signaled when all the tasks captured by vpiEventRecord are completed or when no tasks were captured.

Parameters

[in]

event

An event handle.

Returns

an error code on failure else VPI_SUCCESS