Function: create_context

Description

Explicitly creates a context in the calling process or thread.

For the Atlas 200I/500 A2 inference product , the context contains two streams: one default stream and one stream for internal synchronization.

For the Atlas training product , the context contains one default stream.

For the Atlas A2 training product / Atlas A2 inference product , the context contains one default stream.

For the Atlas inference product , in Ascend EP form, the context contains two streams: one default stream and one stream for internal synchronization.

For the Atlas A3 training product / Atlas A3 inference product , the context contains one default stream.

If acl.rt.set_device is not called in the application, when acl.rt.create_context is called for the first time, the system binds a default stream to the device based on the device ID passed by the API (one device is bound to only one default stream). Therefore, when acl.rt.create_context is called for the first time, the number of occupied streams is calculated as follows: Number of occupied streams = Number of default streams bound to the device + Number of streams contained in the context.

Prototype

C Prototype

        
             aclError aclrtCreateContext(aclrtContext *context, int32_t deviceId)

Python Function

        
             context, ret = acl.rt.create_context(device_id)

Parameters

Parameter	Description
device_id	Int, ID of the device for which the context is to be created.

Return Value

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

Restrictions

The following application scenarios are supported:

If the acl.rt.create_context API is not called to display the created context, the system uses the default context, which is created implicitly when acl.rt.set_device is called.
- Implicit context creation: applies to simple apps with low complicity of interaction logic. However, in multithreaded programming, the execution result depends on the thread scheduling sequence.
- Explicit context creation: applies to large apps with complex interaction logic, offering better app readability and maintainability.
If a device is specified in a process, multiple threads in the process can share the context explicitly created on the device by calling acl.rt.create_context.
If multiple contexts are created in a process (the number of contexts is related to the number of streams, which is limited. For details, see acl.rt.create_stream), the current thread can use only one context at a time. You are advised to specify the context of the current thread by calling acl.rt.set_context to improve program maintainability.

Reference

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

Parent topic: Context Management