Function: create_stream

Applicability

Product	Supported (√/x)
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	√

Function Usage

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 acl.rt.create_stream_with_config.

If the stream creation API is not explicitly called, each context has a default stream that is implicitly created with the acl.rt.set_device or acl.rt.create_context 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

C Prototype

        
             aclError aclrtCreateStream(aclrtStream *stream)

Python Function
1

stream, ret = acl.rt.create_stream()

Parameter Description

None.

Return Value Description

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

Restrictions

Each context has a default stream that is implicitly created with the acl.rt.set_device or acl.rt.create_context call. The priority of the default stream cannot be set, and it is assigned the highest priority. You are advised to use aclrtCreateStream to explicitly create a stream.
- Implicit stream creation: applies to simple apps with low complexity 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
Atlas A3 Training Series Product Atlas A2 Training Series Product/Atlas 800I A2 Inference Product	1,984
Atlas 200/500 A2 Inference Product	512
Atlas Inference Series Product	1,024
Atlas Training Series Product	2,048 In the multi-process scenario, if the total number of streams created at once is close to 2,048, stream creation may fail. In this case, you are advised to perform the following operations: Clear redundant streams. Adjust the code logic to create streams batch by batch. For example, create some streams in the first batch, then the second batch, until the total number of streams is close to 2,048.

Reference

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

Parent topic: Streams Management