Type of stream callback functions.

Add a callback to a compute stream.

Parameters

stream

- Stream to add callback to

callback

- The function to call once preceding stream operations are complete

userData

- User specified data to be passed to the callback function

flags

- Reserved for future use, must be 0

Returns

cudaSuccess, cudaErrorInvalidResourceHandle, cudaErrorInvalidValue, cudaErrorNotSupported

Description

Adds a callback to be called on the host after all currently enqueued items in the stream have completed. For each cudaStreamAddCallback call, a callback will be executed exactly once. The callback will block later work in the stream until it is finished.

The callback may be passed cudaSuccess or an error code. In the event of a device error, all subsequently executed callbacks will receive an appropriate cudaError_t.

Callbacks must not make any CUDA API calls. Attempting to use CUDA APIs may result in cudaErrorNotPermitted. Callbacks must not perform any synchronization that may depend on outstanding device work or other callbacks that are not mandated to run earlier. Callbacks without a mandated order (in independent streams) execute in undefined order and may be serialized.

For the purposes of Unified Memory, callback execution makes a number of guarantees:

• The callback stream is considered idle for the duration of the callback. Thus, for example, a callback may always use memory attached to the callback stream.

• The start of execution of a callback has the same effect as synchronizing an event recorded in the same stream immediately prior to the callback. It thus synchronizes streams which have been "joined" prior to the callback.

• Adding device work to any stream does not have the effect of making the stream active until all preceding callbacks have executed. Thus, for example, a callback might use global attached memory even if work has been added to another stream, if it has been properly ordered with an event.

• Completion of a callback does not cause a stream to become active except as described above. The callback stream will remain idle if no device work follows the callback, and will remain idle across consecutive callbacks without device work in between. Thus, for example, stream synchronization can be done by signaling from a callback at the end of the stream.

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamWaitEvent, cudaStreamDestroy, cudaMallocManaged, cudaStreamAttachMemAsync, cudaLaunchHostFunc, cuStreamAddCallback

Attach memory to a stream asynchronously.

Parameters

stream

- Stream in which to enqueue the attach operation

devPtr

- Pointer to memory (must be a pointer to managed memory or to a valid host-accessible region of system-allocated memory)

length

- Length of memory (defaults to zero)

flags

- Must be one of cudaMemAttachGlobal, cudaMemAttachHost or cudaMemAttachSingle (defaults to cudaMemAttachSingle)

Returns

cudaSuccess, cudaErrorNotReady, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle

Description

Enqueues an operation in stream to specify stream association of length bytes of memory starting from devPtr. This function is a stream-ordered operation, meaning that it is dependent on, and will only take effect when, previous work in stream has completed. Any previous association is automatically replaced.

devPtr must point to an one of the following types of memories:

• managed memory declared using the __managed__ keyword or allocated with cudaMallocManaged.

• a valid host-accessible region of system-allocated pageable memory. This type of memory may only be specified if the device associated with the stream reports a non-zero value for the device attribute cudaDevAttrPageableMemoryAccess.

For managed allocations, length must be either zero or the entire allocation's size. Both indicate that the entire allocation's stream association is being changed. Currently, it is not possible to change stream association for a portion of a managed allocation.

For pageable allocations, length must be non-zero.

The stream association is specified using flags which must be one of cudaMemAttachGlobal, cudaMemAttachHost or cudaMemAttachSingle. The default value for flags is cudaMemAttachSingle If the cudaMemAttachGlobal flag is specified, the memory can be accessed by any stream on any device. If the cudaMemAttachHost flag is specified, the program makes a guarantee that it won't access the memory on the device from any stream on a device that has a zero value for the device attribute cudaDevAttrConcurrentManagedAccess. If the cudaMemAttachSingle flag is specified and stream is associated with a device that has a zero value for the device attribute cudaDevAttrConcurrentManagedAccess, the program makes a guarantee that it will only access the memory on the device from stream. It is illegal to attach singly to the NULL stream, because the NULL stream is a virtual global stream and not a specific stream. An error will be returned in this case.

When memory is associated with a single stream, the Unified Memory system will allow CPU access to this memory region so long as all operations in stream have completed, regardless of whether other streams are active. In effect, this constrains exclusive ownership of the managed memory region by an active GPU to per-stream activity instead of whole-GPU activity.

Accessing memory on the device from streams that are not associated with it will produce undefined results. No error checking is performed by the Unified Memory system to ensure that kernels launched into other streams do not access this region.

It is a program's responsibility to order calls to cudaStreamAttachMemAsync via events, synchronization or other means to ensure legal access to memory at all times. Data visibility and coherency will be changed appropriately for all kernels which follow a stream-association change.

If stream is destroyed while data is associated with it, the association is removed and the association reverts to the default visibility of the allocation as specified at cudaMallocManaged. For __managed__ variables, the default association is always cudaMemAttachGlobal. Note that destroying a stream is an asynchronous operation, and as a result, the change to default association won't happen until all work in the stream has completed.

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamWaitEvent, cudaStreamSynchronize, cudaStreamAddCallback, cudaStreamDestroy, cudaMallocManaged, cuStreamAttachMemAsync

Begins graph capture on a stream.

Parameters

stream

- Stream in which to initiate capture

mode

- Controls the interaction of this capture sequence with other API calls that are potentially unsafe. For more details see cudaThreadExchangeStreamCaptureMode.

Returns

cudaSuccess, cudaErrorInvalidValue

Description

Begin graph capture on stream. When a stream is in capture mode, all operations pushed into the stream will not be executed, but will instead be captured into a graph, which will be returned via cudaStreamEndCapture. Capture may not be initiated if stream is cudaStreamLegacy. Capture must be ended on the same stream in which it was initiated, and it may only be initiated if the stream is not already in capture mode. The capture mode may be queried via cudaStreamIsCapturing. A unique id representing the capture sequence may be queried via cudaStreamGetCaptureInfo.

If mode is not cudaStreamCaptureModeRelaxed, cudaStreamEndCapture must be called on this stream from the same thread.

See also:

cudaStreamCreate, cudaStreamIsCapturing, cudaStreamEndCapture, cudaThreadExchangeStreamCaptureMode

Create an asynchronous stream.

Parameters

pStream

- Pointer to new stream identifier

Returns

cudaSuccess, cudaErrorInvalidValue

Description

Creates a new asynchronous stream.

See also:

cudaStreamCreateWithPriority, cudaStreamCreateWithFlags, cudaStreamGetPriority, cudaStreamGetFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamDestroy, cuStreamCreate

Create an asynchronous stream.

Parameters

pStream

- Pointer to new stream identifier

flags

- Parameters for stream creation

Returns

cudaSuccess, cudaErrorInvalidValue

Description

Creates a new asynchronous stream. The flags argument determines the behaviors of the stream. Valid values for flags are

• cudaStreamDefault: Default stream creation flag.

• cudaStreamNonBlocking: Specifies that work running in the created stream may run concurrently with work in stream 0 (the NULL stream), and that the created stream should perform no implicit synchronization with stream 0.

See also:

cudaStreamCreate, cudaStreamCreateWithPriority, cudaStreamGetFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamDestroy, cuStreamCreate

Create an asynchronous stream with the specified priority.

Parameters

pStream

- Pointer to new stream identifier

flags

- Flags for stream creation. See cudaStreamCreateWithFlags for a list of valid flags that can be passed

priority

- Priority of the stream. Lower numbers represent higher priorities. See cudaDeviceGetStreamPriorityRange for more information about the meaningful stream priorities that can be passed.

Returns

cudaSuccess, cudaErrorInvalidValue

Description

Creates a stream with the specified priority and returns a handle in pStream. This API alters the scheduler priority of work in the stream. Work in a higher priority stream may preempt work already executing in a low priority stream.

priority follows a convention where lower numbers represent higher priorities. '0' represents default priority. The range of meaningful numerical priorities can be queried using cudaDeviceGetStreamPriorityRange. If the specified priority is outside the numerical range returned by cudaDeviceGetStreamPriorityRange, it will automatically be clamped to the lowest or the highest number in the range.

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaDeviceGetStreamPriorityRange, cudaStreamGetPriority, cudaStreamQuery, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamSynchronize, cudaStreamDestroy, cuStreamCreateWithPriority

Destroys and cleans up an asynchronous stream.

Parameters

stream

- Stream identifier

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle

Description

Destroys and cleans up the asynchronous stream specified by stream.

In case the device is still doing work in the stream stream when cudaStreamDestroy() is called, the function will return immediately and the resources associated with stream will be released automatically once the device has completed all work in stream.

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamWaitEvent, cudaStreamSynchronize, cudaStreamAddCallback, cuStreamDestroy

Ends capture on a stream, returning the captured graph.

Parameters

stream

- Stream to query

pGraph

- The captured graph

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorStreamCaptureWrongThread

Description

End capture on stream, returning the captured graph via pGraph. Capture must have been initiated on stream via a call to cudaStreamBeginCapture. If capture was invalidated, due to a violation of the rules of stream capture, then a NULL graph will be returned.

If the mode argument to cudaStreamBeginCapture was not cudaStreamCaptureModeRelaxed, this call must be from the same thread as cudaStreamBeginCapture.

See also:

cudaStreamCreate, cudaStreamBeginCapture, cudaStreamIsCapturing

Query capture status of a stream.

Parameters

stream

- Stream to query

pCaptureStatus

- Returns the stream's capture status

pId

- Returns the unique id of the capture sequence

Returns

cudaSuccess, cudaErrorStreamCaptureImplicit

Description

Query the capture status of a stream and get a unique id representing the capture sequence over the lifetime of the process.

If called on cudaStreamLegacy (the "null stream") while a stream not created with cudaStreamNonBlocking is capturing, returns cudaErrorStreamCaptureImplicit.

A valid id is returned only if both of the following are true:

• the call returns cudaSuccess

• captureStatus is set to cudaStreamCaptureStatusActive

See also:

cudaStreamBeginCapture, cudaStreamIsCapturing

Query the flags of a stream.

Parameters

hStream

- Handle to the stream to be queried

flags

- Pointer to an unsigned integer in which the stream's flags are returned

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle

Description

Query the flags of a stream. The flags are returned in flags. See cudaStreamCreateWithFlags for a list of valid flags.

See also:

cudaStreamCreateWithPriority, cudaStreamCreateWithFlags, cudaStreamGetPriority, cuStreamGetFlags

Query the priority of a stream.

Parameters

hStream

- Handle to the stream to be queried

priority

- Pointer to a signed integer in which the stream's priority is returned

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle

Description

Query the priority of a stream. The priority is returned in in priority. Note that if the stream was created with a priority outside the meaningful numerical range returned by cudaDeviceGetStreamPriorityRange, this function returns the clamped priority. See cudaStreamCreateWithPriority for details about priority clamping.

See also:

cudaStreamCreateWithPriority, cudaDeviceGetStreamPriorityRange, cudaStreamGetFlags, cuStreamGetPriority

Returns a stream's capture status.

Parameters

stream

- Stream to query

pCaptureStatus

- Returns the stream's capture status

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorStreamCaptureImplicit

Description

Return the capture status of stream via pCaptureStatus. After a successful call, *pCaptureStatus will contain one of the following:

• cudaStreamCaptureStatusNone: The stream is not capturing.

• cudaStreamCaptureStatusActive: The stream is capturing.

• cudaStreamCaptureStatusInvalidated: The stream was capturing but an error has invalidated the capture sequence. The capture sequence must be terminated with cudaStreamEndCapture on the stream where it was initiated in order to continue using stream.

Note that, if this is called on cudaStreamLegacy (the "null stream") while a blocking stream on the same device is capturing, it will return cudaErrorStreamCaptureImplicit and *pCaptureStatus is unspecified after the call. The blocking stream capture is not invalidated.

When a blocking stream is capturing, the legacy stream is in an unusable state until the blocking stream capture is terminated. The legacy stream is not supported for stream capture, but attempted use would have an implicit dependency on the capturing stream(s).

See also:

cudaStreamCreate, cudaStreamBeginCapture, cudaStreamEndCapture

Queries an asynchronous stream for completion status.

Parameters

stream

- Stream identifier

Returns

cudaSuccess, cudaErrorNotReady, cudaErrorInvalidResourceHandle

Description

Returns cudaSuccess if all operations in stream have completed, or cudaErrorNotReady if not.

For the purposes of Unified Memory, a return value of cudaSuccess is equivalent to having called cudaStreamSynchronize().

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamWaitEvent, cudaStreamSynchronize, cudaStreamAddCallback, cudaStreamDestroy, cuStreamQuery

Waits for stream tasks to complete.

Parameters

stream

- Stream identifier

Returns

cudaSuccess, cudaErrorInvalidResourceHandle

Description

Blocks until stream has completed all operations. If the cudaDeviceScheduleBlockingSync flag was set for this device, the host thread will block until the stream is finished with all of its tasks.

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamDestroy, cuStreamSynchronize

Make a compute stream wait on an event.

Parameters

stream

- Stream to wait

event

- Event to wait on

flags

- Parameters for the operation (must be 0)

Returns

cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle

Description

Makes all future work submitted to stream wait for all work captured in event. See cudaEventRecord() for details on what is captured by an event. The synchronization will be performed efficiently on the device when applicable. event may be from a different device than stream.

See also:

cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamAddCallback, cudaStreamDestroy, cuStreamWaitEvent

Swaps the stream capture interaction mode for a thread.

Parameters

mode

- Pointer to mode value to swap with the current mode

Returns

cudaSuccess, cudaErrorInvalidValue

Description

Sets the calling thread's stream capture interaction mode to the value contained in *mode, and overwrites *mode with the previous mode for the thread. To facilitate deterministic behavior across function or module boundaries, callers are encouraged to use this API in a push-pop fashion:

‎     cudaStreamCaptureMode mode = desiredMode;
           cudaThreadExchangeStreamCaptureMode(&mode);
           ...
           cudaThreadExchangeStreamCaptureMode(&mode); // restore previous mode

During stream capture (see cudaStreamBeginCapture), some actions, such as a call to cudaMalloc, may be unsafe. In the case of cudaMalloc, the operation is not enqueued asynchronously to a stream, and is not observed by stream capture. Therefore, if the sequence of operations captured via cudaStreamBeginCapture depended on the allocation being replayed whenever the graph is launched, the captured graph would be invalid.

Therefore, stream capture places restrictions on API calls that can be made within or concurrently to a cudaStreamBeginCapture-cudaStreamEndCapture sequence. This behavior can be controlled via this API and flags to cudaStreamBeginCapture.

A thread's mode is one of the following:

• cudaStreamCaptureModeGlobal: This is the default mode. If the local thread has an ongoing capture sequence that was not initiated with cudaStreamCaptureModeRelaxed at cuStreamBeginCapture, or if any other thread has a concurrent capture sequence initiated with cudaStreamCaptureModeGlobal, this thread is prohibited from potentially unsafe API calls.

• cudaStreamCaptureModeThreadLocal: If the local thread has an ongoing capture sequence not initiated with cudaStreamCaptureModeRelaxed, it is prohibited from potentially unsafe API calls. Concurrent capture sequences in other threads are ignored.

• cudaStreamCaptureModeRelaxed: The local thread is not prohibited from potentially unsafe API calls. Note that the thread is still prohibited from API calls which necessarily conflict with stream capture, for example, attempting cudaEventQuery on an event that was last recorded inside a capture sequence.

See also:

cudaStreamBeginCapture