aclrtCreateStream

Applicability

Product	Supported
Atlas 350 Accelerator Card	√
Atlas A3 training product / Atlas A3 inference product	√
Atlas A2 training product / Atlas A2 inference product	√
Atlas 200I/500 A2 inference product	√
Atlas inference product	√
Atlas training product	√

Description

Creates a stream.

This API does not allow for adjusting the stream priority. By default, streams are assigned the highest priority if none is specified. For details about how to set the priority when creating a stream, see aclrtCreateStreamWithConfig.

If the stream creation API is not explicitly called, each context has a default stream that is implicitly created with the aclrtSetDevice or aclrtCreateContext call. The priority of the default stream cannot be set, and it is assigned the highest priority. Default streams apply to simple apps with low complexity of interaction logic. However, in multithreaded programming, the execution result depends on the thread scheduling sequence. Explicit stream creation (recommended) applies to large-scale applications with complex interaction logic, improving application readability and maintainability.

Prototype

      
           aclError aclrtCreateStream(aclrtStream *stream)

Parameters

Parameter	Input/Output	Description
stream	Output	Stream pointer. For details about the type definition, see aclrtStream.

Returns

0 on success; otherwise, failure. For details, see aclError.

Restrictions

The maximum number of streams supported by hardware varies depending on the hardware model. If multiple streams (including the default stream and the stream for internal synchronization) exist, only N streams can be explicitly created, where N = Maximum number of streams – Number of existing streams. For example, if the maximum number of streams is 1,024 and there are already two streams, you can only call this API to explicitly create 1,022 streams.

Model	Maximum Number of Streams
Atlas 350 Accelerator Card Atlas A3 training product / Atlas A3 inference product Atlas A2 training product / Atlas A2 inference product	1984
Atlas 200I/500 A2 inference product	512
Atlas inference product	1024 In the Ascend EP form, there is a stream for internal synchronization.
Atlas training product	2048 In the multi-process scenario, if the total number of streams created at a time is close to 2,048, streams may fail to be created. In this case, you are advised to perform the following operations: Clear redundant streams. Adjust the code logic to create streams in batches. For instance, create a certain number of streams in the first batch, then create some more in the second batch, and continue this process until the total number of streams approaches 2048.

API Call Example

For the API call example, see Stream Creation and Destruction.

Parent topic: Stream Management