The receive_message function pauses the Python process and waits until a message is received over the network. The function definition is:

def receive_message():

This function returns the received message (type is dictionary).

For example, suppose we called

message = receive_message()

Then Python is going to update the LWOS Python state as follows:

• Hostname: "b.com"
• Python
  • Status: "BLOCKED",
  • System Call
    • Type: "NETWORK"
    • Mode: "READ"
    • Hostname: null
    • Data: null
  • Values Stack:
    • [ ]
    • [ ]
  • Expression Stack:
    • [ ]
    • receive_message()

Python -> Status is now "BLOCKED." This prompts LWOS to inspect Python -> System Call. When Python -> System Call -> Type is "NETWORK" and Mode is "READ," LWOS updates Status to "WAITING_ON_NETWORK." The computer then sits idle until it receives a message.

Suppose that at some point, the connected network device updates the Network property and interrupts b.com as follows:

• Hostname: "b.com"
• Status: "WAITING_ON_NETWORK"
• Interrupts:
  • Network: true
• Command: "python"
• Network
  • Hostname: "a.com"
  • Data: "GET /articles/Best_Gadgets HTTP/1.1"
  • Signal: false

LWOS received a message from a.com. When command is python and the Status is "WAITING_ON_NETWORK," LWOS copies Network -> Hostname to Python -> System Call -> Hostname and Network -> Data to Python -> System Call -> Data. LWOS then resumes the Python process by updating Python -> Status to "SYSCALL_COMPLETE." Here is the updated LWOS Python state:

• Python
  • Status: "SYSCALL_COMPLETE"
  • System Call
    • Type: "NETWORK"
    • Mode: "READ",
    • Hostname: "a.com"
    • Data: "GET /articles/Best_Gadgets HTTP/1.1"
  • Values Stack:
    • [ ]
    • [ ]
  • Expression Stack:
    • [ ]
    • receive_message()

Python then constructs the following Python dictionary object from the received data:

• hostname: "a.com"
• message: "GET /articles/Best_Gadgets HTTP/1.1"

Python appends the new dictionary to the Object Store and pushes the reference to this object to the Values Stack. Here is the updated python state:

• Python
  • Status: "SYSCALL_COMPLETE"
  • Values Stack:
    • Python reference 0
  • Expression Stack:
    • [ ]
  • Object Store:
    • 0
      • hostname: "a.com"
      • message: "GET /articles/Best_Gadgets HTTP/1.1"

The receive_message function call is now complete. Python then pops the top of the Values Stack and stores the popped element (Python reference 0) in a new variable message as follows:

• Python
  • Status: "RUNNING"
  • Variables:
    • entry message: Python reference 0