Blocking vs Non-blocking

Blocking and Non-blocking

→ From the perspective of control

Blocking

• Waiting until I/O finishes

  • why?

    • Because the function does not return until it finishes

• The user process suspends work and waits until the kernel completes the task

• Since I/O operations barely use CPU resources, the blocking approach results in significant CPU resource waste

• Blocking is done for synchronization

Blocking vs Synchronous

• If it is not mandatory to stay in the wait queue while waiting for the system's return, it is synchronous

• If it is mandatory to stay in the wait queue while waiting for the system's return, it is blocking

Non-blocking

• Created to overcome the inefficiency of the blocking approach

• Does not suspend the user process's work while I/O operations are in progress

• When the user process makes a function call (system call) to the kernel for I/O processing, the kernel returns a result immediately regardless of the function's progress

  • The result returned at this point is the data that can be retrieved at that moment

  • Initially there may be no data to retrieve, but over time, data becomes available

• Problem

  • The client must continuously check whether the returned value has reached the desired size (polling)

    • In the process of checking whether the returned data is ready (whether it has reached the desired value), if numerous client requests occur simultaneously, it can place a significant burden on the CPU

Non-blocking vs Asynchronous

• If the result (data) is returned along with the system call return, it is non-blocking

• If the result (data) is not returned along with the system call return, it is asynchronous

• Summary

  • The asynchronous approach delivers data through callback functions, events, or signals

  • The non-blocking approach includes data with every system call return, and checks whether the returned data has fully arrived as requested

Blocking vs Non-blocking

• If the application enters the OS wait queue during execution and sends a response after the system call for the request is completed, it is blocking

• If the application does not enter the OS wait queue during execution and sends a response immediately regardless of execution status, it is non-blocking

Summary

• Blocking vs Non-Blocking → From the perspective of control

• Sync vs Async → From the perspective of order and result (processing)