The ultimate guide to senior engineering interviews. Strategies developed by FAANG engineers on Python concurrency, multithreading, monitors, and event loops. Prep faster for top company questions.

Concurrency in Python is one of the most complex and advanced topics brought up during senior engineering interviews. Knowledge of concurrency and multithreading can put interviewees at a considerable advantage. This course lays the foundations of advanced concurrency and multithreading and explains concepts such as Monitors, Event Loops and Deferred Callbacks in depth. It also builds simple and complete solutions to popular concurrency problems that can be asked about in interviews like the Reader-Writer Problem and the Dining Philosopher Problem. While prior knowledge of concurrency is not required to follow through with this course, familiarity with the very basic Python would be helpful.

Python Concurrency for Senior Engineering Interviews

<div class="card">
   # Fork   
   <div class="ans">
<p>Fork is the default method Python uses to create processes on Unix based systems.</p>

<p>Fork is one of the options a developer can choose to create processes. We'll need to examine the underlying operating system's fork system call in order to understand how the fork option works in Python.</p>

## Fork system call
<p>There are two families of system calls, <b>fork</b> and <b>exec</b> that can be invoked by a process to create subprocesses on Unix based systems. A process can invoke this system call and get an <i>almost</i> clone of itself. We qualify the statement with <i>almost</i> because not everything is copied when a fork happens. The exact list of what isn't copied can be found by checking out the manpage of fork on your platform (type "man fork" in terminal). The child process gets an identical memory image so any open file descriptors are copied. However, multiple threads of a process don't get copied. Any threads running in the parent process do not exist in the child process. Additionally, fork isn't available on a Windows platform. Under the hood, Python uses <code class="mthd">os.fork()</code> to create the child process.</p>

<p>Often times we don't want to fork processes because the newly created process (called the child process) comes with identical copies of data-structures and file descriptors of the parent process, which can be problematic.</p>

<p>To illustrate the differences with other methods of creating processes, consider the snippet below:</p>
### 
<b>

```python
from multiprocessing import Process
import multiprocessing

class Test:
    value = 777


def process_task():
    print(Test.value)


if __name__ == '__main__':
    multiprocessing.set_start_method('fork')

    # change the value of Test.value before creating
    # a new process
    Test.value = 999
    process = Process(target=process_task, name="process-1")
    process.start()
    process.join()

``` 
</b>
<p>In the snippet above, the forked child process executes the method <code class="mthd">process_task()</code>. The main process changes the value of a static variable <code class="mthd">Test.value</code> from 777 to 999 just before it forks the child process. The child process gets a copy of all the resources of the parent, including the static variable and prints a value of 999.</p>
</div>
</div>


<div>
   # Fork   
   <div>
<p>Fork is the default method Python uses to create processes on Unix based systems.</p>

<p>Fork is one of the options a developer can choose to create processes. We'll need to examine the underlying operating system's fork system call in order to understand how the fork option works in Python.</p>

## Fork system call
<p>There are two families of system calls, <b>fork</b> and <b>exec</b> that can be invoked by a process to create subprocesses on Unix based systems. A process can invoke this system call and get an <i>almost</i> clone of itself. We qualify the statement with <i>almost</i> because not everything is copied when a fork happens. The exact list of what isn't copied can be found by checking out the manpage of fork on your platform (type "man fork" in terminal). The child process gets an identical memory image so any open file descriptors are copied. However, multiple threads of a process don't get copied. Any threads running in the parent process do not exist in the child process. Additionally, fork isn't available on a Windows platform. Under the hood, Python uses <code>os.fork()</code> to create the child process.</p>

<p>Often times we don't want to fork processes because the newly created process (called the child process) comes with identical copies of data-structures and file descriptors of the parent process, which can be problematic.</p>

<p>To illustrate the differences with other methods of creating processes, consider the snippet below:</p>
### 
<b>

```python
from multiprocessing import Process
import multiprocessing

class Test:
    value = 777


def process_task():
    print(Test.value)


if __name__ == '__main__':
    multiprocessing.set_start_method('fork')

    # change the value of Test.value before creating
    # a new process
    Test.value = 999
    process = Process(target=process_task, name="process-1")
    process.start()
    process.join()

``` 
</b>
<p>In the snippet above, the forked child process executes the method <code>process_task()</code>. The main process changes the value of a static variable <code>Test.value</code> from 777 to 999 just before it forks the child process. The child process gets a copy of all the resources of the parent, including the static variable and prints a value of 999.</p>
</div>
</div>


This lesson discusses the caveats to remember when forking processes.

The Basics

Threading Module

Multiprocessing

Concurrent Package

Async.io

Global Interpreter Lock

Interview Practise Problems

The End

Fork

Fork

Fork system call