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CUDART_STREAM(3)

version 6.0
8 Feb 2019
Aliases: cudaStreamAddCallback(3), cudaStreamAddCallback(3), cudaStreamAttachMemAsync(3), cudaStreamAttachMemAsync(3), cudaStreamBeginCapture(3), cudaStreamCallback_t(3), cudaStreamCallback_t(3), cudaStreamCreate(3), cudaStreamCreate(3), cudaStreamCreateWithFlags(3), cudaStreamCreateWithFlags(3), cudaStreamCreateWithPriority(3), cudaStreamCreateWithPriority(3), cudaStreamDestroy(3), cudaStreamDestroy(3), cudaStreamEndCapture(3), cudaStreamGetCaptureInfo(3), cudaStreamGetFlags(3), cudaStreamGetFlags(3), cudaStreamGetPriority(3), cudaStreamGetPriority(3), cudaStreamIsCapturing(3), cudaStreamQuery(3), cudaStreamQuery(3), cudaStreamSynchronize(3), cudaStreamSynchronize(3), cudaStreamWaitEvent(3), cudaStreamWaitEvent(3), cudaThreadExchangeStreamCaptureMode(3)

nvidia-cuda-dev

NVIDIA CUDA development files

cuda

NVIDIA's GPU programming toolkit

NAME

Stream Management -

Typedefs

typedef void(CUDART_CB * cudaStreamCallback_t )(cudaStream_t stream, cudaError_t status, void *userData)

Functions

cudaError_t cudaStreamAddCallback (cudaStream_t stream, cudaStreamCallback_t callback, void *userData, unsigned int flags)
Add a callback to a compute stream. __cudart_builtin__ cudaError_t cudaStreamAttachMemAsync (cudaStream_t stream, void *devPtr, size_t length=0, unsigned int flags=0x04)
Attach memory to a stream asynchronously. cudaError_t cudaStreamBeginCapture (cudaStream_t stream, enum cudaStreamCaptureMode mode)
Begins graph capture on a stream. cudaError_t cudaStreamCreate (cudaStream_t *pStream)
Create an asynchronous stream. __cudart_builtin__ cudaError_t cudaStreamCreateWithFlags (cudaStream_t *pStream, unsigned int flags)
Create an asynchronous stream. __cudart_builtin__ cudaError_t cudaStreamCreateWithPriority (cudaStream_t *pStream, unsigned int flags, int priority)
Create an asynchronous stream with the specified priority. __cudart_builtin__ cudaError_t cudaStreamDestroy (cudaStream_t stream)
Destroys and cleans up an asynchronous stream. cudaError_t cudaStreamEndCapture (cudaStream_t stream, cudaGraph_t *pGraph)
Ends capture on a stream, returning the captured graph. cudaError_t cudaStreamGetCaptureInfo (cudaStream_t stream, enum cudaStreamCaptureStatus *pCaptureStatus, unsigned long long *pId)
Query capture status of a stream. __cudart_builtin__ cudaError_t cudaStreamGetFlags (cudaStream_t hStream, unsigned int *flags)
Query the flags of a stream. __cudart_builtin__ cudaError_t cudaStreamGetPriority (cudaStream_t hStream, int *priority)
Query the priority of a stream. cudaError_t cudaStreamIsCapturing (cudaStream_t stream, enum cudaStreamCaptureStatus *pCaptureStatus)
Returns a stream’s capture status. cudaError_t cudaStreamQuery (cudaStream_t stream)
Queries an asynchronous stream for completion status. cudaError_t cudaStreamSynchronize (cudaStream_t stream)
Waits for stream tasks to complete. __cudart_builtin__ cudaError_t cudaStreamWaitEvent (cudaStream_t stream, cudaEvent_t event, unsigned int flags)
Make a compute stream wait on an event. cudaError_t cudaThreadExchangeStreamCaptureMode (enum cudaStreamCaptureMode *mode)
Swaps the stream capture interaction mode for a thread.

Detailed Description

\brief stream management functions of the CUDA runtime API (cuda_runtime_api.h)
This section describes the stream management functions of the CUDA runtime application programming interface.

Typedef Documentation

typedef void(CUDART_CB * cudaStreamCallback_t)(cudaStream_t stream, cudaError_t status, void *userData)

Type of stream callback functions.
Parameters:
stream The stream as passed to cudaStreamAddCallback, may be NULL.
status cudaSuccess or any persistent error on the stream.
userData User parameter provided at registration.

Function Documentation

cudaError_t cudaStreamAddCallback (cudaStream_t stream, cudaStreamCallback_t callback, void * userData, unsigned int flags)

Note:
This function is slated for eventual deprecation and removal. If you do not require the callback to execute in case of a device error, consider using cudaLaunchHostFunc. Additionally, this function is not supported with cudaStreamBeginCapture and cudaStreamEndCapture, unlike cudaLaunchHostFunc.
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:
o 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.
o 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.
o 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.
o 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.
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
Note:
This function uses standard semantics.
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamWaitEvent, cudaStreamDestroy, cudaMallocManaged, cudaStreamAttachMemAsync, cudaLaunchHostFunc, cuStreamAddCallback

__cudart_builtin__ cudaError_t cudaStreamAttachMemAsync (cudaStream_t stream, void * devPtr, size_t length = 0, unsigned int flags = 0x04)

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:
o managed memory declared using the __managed__ keyword or allocated with cudaMallocManaged.
o 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.
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
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamWaitEvent, cudaStreamSynchronize, cudaStreamAddCallback, cudaStreamDestroy, cudaMallocManaged, cuStreamAttachMemAsync
Parameters:
flags Memory can only be accessed by a single stream on the associated device

cudaError_t cudaStreamBeginCapture (cudaStream_t stream, enum cudaStreamCaptureMode mode)

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.
Note:
Kernels captured using this API must not use texture and surface references. Reading or writing through any texture or surface reference is undefined behavior. This restriction does not apply to texture and surface objects.
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
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamIsCapturing, cudaStreamEndCapture, cudaThreadExchangeStreamCaptureMode

cudaError_t cudaStreamCreate (cudaStream_t * pStream)

Creates a new asynchronous stream.
Parameters:
pStream - Pointer to new stream identifier
Returns:
cudaSuccess, cudaErrorInvalidValue
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreateWithPriority, cudaStreamCreateWithFlags, cudaStreamGetPriority, cudaStreamGetFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamDestroy, cuStreamCreate

__cudart_builtin__ cudaError_t cudaStreamCreateWithFlags (cudaStream_t * pStream, unsigned int flags)

Creates a new asynchronous stream. The flags argument determines the behaviors of the stream. Valid values for flags are
o cudaStreamDefault: Default stream creation flag.
o 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.
Parameters:
pStream - Pointer to new stream identifier
flags - Parameters for stream creation
Returns:
cudaSuccess, cudaErrorInvalidValue
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithPriority, cudaStreamGetFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamDestroy, cuStreamCreate

__cudart_builtin__ cudaError_t cudaStreamCreateWithPriority (cudaStream_t * pStream, unsigned int flags, int priority)

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.
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
Note:
Note that this function may also return error codes from previous, asynchronous launches.
Stream priorities are supported only on GPUs with compute capability 3.5 or higher.
In the current implementation, only compute kernels launched in priority streams are affected by the stream’s priority. Stream priorities have no effect on host-to-device and device-to-host memory operations.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaDeviceGetStreamPriorityRange, cudaStreamGetPriority, cudaStreamQuery, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamSynchronize, cudaStreamDestroy, cuStreamCreateWithPriority

__cudart_builtin__ cudaError_t cudaStreamDestroy (cudaStream_t stream)

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.
Parameters:
stream - Stream identifier
Returns:
cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle
Note:
This function uses standard semantics.
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamWaitEvent, cudaStreamSynchronize, cudaStreamAddCallback, cuStreamDestroy

cudaError_t cudaStreamEndCapture (cudaStream_t stream, cudaGraph_t * pGraph)

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.
Parameters:
stream - Stream to query
pGraph - The captured graph
Returns:
cudaSuccess, cudaErrorInvalidValue, cudaErrorStreamCaptureWrongThread
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamBeginCapture, cudaStreamIsCapturing

cudaError_t cudaStreamGetCaptureInfo (cudaStream_t stream, enum cudaStreamCaptureStatus * pCaptureStatus, unsigned long long * pId)

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:
o the call returns cudaSuccess
o captureStatus is set to cudaStreamCaptureStatusActive
Parameters:
stream - Stream to query
pCaptureStatus - Returns the stream’s capture status
pId - Returns the unique id of the capture sequence
Returns:
cudaSuccess, cudaErrorStreamCaptureImplicit
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamBeginCapture, cudaStreamIsCapturing

__cudart_builtin__ cudaError_t cudaStreamGetFlags (cudaStream_t hStream, unsigned int * flags)

Query the flags of a stream. The flags are returned in flags. See cudaStreamCreateWithFlags for a list of valid flags.
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
Note:
This function uses standard semantics.
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreateWithPriority, cudaStreamCreateWithFlags, cudaStreamGetPriority, cuStreamGetFlags

__cudart_builtin__ cudaError_t cudaStreamGetPriority (cudaStream_t hStream, int * priority)

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.
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
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreateWithPriority, cudaDeviceGetStreamPriorityRange, cudaStreamGetFlags, cuStreamGetPriority

cudaError_t cudaStreamIsCapturing (cudaStream_t stream, enum cudaStreamCaptureStatus * pCaptureStatus)

Return the capture status of stream via pCaptureStatus. After a successful call, *pCaptureStatus will contain one of the following:
o cudaStreamCaptureStatusNone: The stream is not capturing.
o cudaStreamCaptureStatusActive: The stream is capturing.
o 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).
Parameters:
stream - Stream to query
pCaptureStatus - Returns the stream’s capture status
Returns:
cudaSuccess, cudaErrorInvalidValue, cudaErrorStreamCaptureImplicit
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamBeginCapture, cudaStreamEndCapture

cudaError_t cudaStreamQuery (cudaStream_t stream)

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().
Parameters:
stream - Stream identifier
Returns:
cudaSuccess, cudaErrorNotReady, cudaErrorInvalidResourceHandle
Note:
This function uses standard semantics.
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamWaitEvent, cudaStreamSynchronize, cudaStreamAddCallback, cudaStreamDestroy, cuStreamQuery

cudaError_t cudaStreamSynchronize (cudaStream_t stream)

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.
Parameters:
stream - Stream identifier
Returns:
cudaSuccess, cudaErrorInvalidResourceHandle
Note:
This function uses standard semantics.
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamWaitEvent, cudaStreamAddCallback, cudaStreamDestroy, cuStreamSynchronize

__cudart_builtin__ cudaError_t cudaStreamWaitEvent (cudaStream_t stream, cudaEvent_t event, unsigned int flags)

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.
Parameters:
stream - Stream to wait
event - Event to wait on
flags - Parameters for the operation (must be 0)
Returns:
cudaSuccess, cudaErrorInvalidValue, cudaErrorInvalidResourceHandle
Note:
This function uses standard semantics.
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamCreate, cudaStreamCreateWithFlags, cudaStreamQuery, cudaStreamSynchronize, cudaStreamAddCallback, cudaStreamDestroy, cuStreamWaitEvent

cudaError_t cudaThreadExchangeStreamCaptureMode (enum cudaStreamCaptureMode * mode)

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:
o 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.
o 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.
o 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.
Parameters:
mode - Pointer to mode value to swap with the current mode
Returns:
cudaSuccess, cudaErrorInvalidValue
Note:
Note that this function may also return error codes from previous, asynchronous launches.
See also:
cudaStreamBeginCapture

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