Documentation

Function: create_context

C Prototype

aclError aclrtCreateContext(aclrtContext *context, int32_t deviceId)

Python Function

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

Function Usage

Explicitly creates a context in the calling process or thread.

For the Atlas 200/300/500 Inference Product, the context contains two streams: one default stream and one stream for internal synchronization.

For the Atlas Training Series Product, the context contains one default stream.

NOTE:

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.

Input Description

device_id: int, ID of the device for which the context is to be created.

Return Value

context: int, pointer address of the created context.

ret: int, error code.

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 current thread can use only one context at a time. It is recommended that acl.rt.set_context be used to specify the context of the current thread to improve program maintainability. The number of contexts depends on the number of streams. For details, see acl.rt.create_stream.

Reference

For details about the API call sequence and example, see Runtime Resource Allocation and Deallocation.
Parent topic: Context Management