Asterisk queue agent status Mechanism Analysis

The final obtaining of the agent status is to call devicestate. in C, the ast_device_state is obtained. When the queue module is initialized, it registers the callback function for device status change, devicestate. c starts the thread do_devstate_changes when the system starts, constantly calls ast_device_state to get the device status, and updates the agent status based on the callback function registered during queue initialization, the ast_device_state function provides two methods to obtain the device status. One is to call the device status query function provided by the protocol stack when the protocol stack supports the device status, such as the SIP protocol stack, which is obtained through the sip_devicestate function, the other is to retrieve the agent status by traversing the channel composed of the agent interface.