Applicable Products

Product	Supported (√/x)
Ascend 950PR / Ascend 950DT	√
Atlas A3 training products / Atlas A3 inference products	√
Atlas A2 training products / Atlas A2 inference products	√
Atlas training products	√
Atlas inference products	√
Atlas 200I/500 A2 inference products	√

Description

Creates a stream in the calling process or thread.

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 the acl.rt.create_stream_with_config API.

If the stream creation API is not explicitly called, each context corresponds to a default stream. The default stream is implicitly created by calling the acl.rt.set_device or acl.rt.create_context API. The priority of the default stream cannot be set and is the highest priority. The default stream is suitable for simple applications without complex interaction logic. However, in multithreaded programming, the execution result depends on the thread scheduling sequence. Explicitly created streams are suitable for large-scale applications with complex interaction logic to improve program readability and maintainability. Therefore, explicit streams are recommended.

Prototype

C Prototype

        
             aclError aclrtCreateStream(aclrtStream *stream)

Python Function
1

stream, ret = acl.rt.create_stream()

Parameters

None

Return Values

Return Value	Description
stream	Int, pointer address of the created context.
ret	Int, error code. 0 on success; else, failure.

Restrictions

Each context corresponds to a default stream. The default stream is implicitly created by calling the acl.rt.set_device or acl.rt.create_context API. The priority of the default stream cannot be set and is the highest priority. You are advised to use aclrtCreateStream to explicitly create a stream.
- Implicit stream creation: applies to simple apps with low complicity of interaction logic. However, in multithreaded programming, the execution result depends on the thread scheduling sequence.
- (Recommended) Explicit stream creation: applies to large apps with complex interaction logic, offering better app readability and maintainability.
The maximum number of streams supported by hardware varies depending on the hardware model. If multiple streams (including the default streams and the streams 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
Ascend 950PR / Ascend 950DT	1,984
Atlas A3 training products / Atlas A3 inference products	1,984
Atlas A2 training products / Atlas A2 inference products	1,984
Atlas 200I/500 A2 inference products	512
Atlas inference products	1,024 In the Ascend EP form, there is a stream for internal synchronization.
Atlas training products	2,048 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 example, create some streams in the first batch, then the second batch, and so on until the total number of streams is close to 2,048.

Reference

For details about the API call sequence and examples, see Runtime Resource Allocation and Deallocation.