PCPP2 Interprocess Communication — 20 Questions

Question 1

When using a multiprocessing.Queue to share data between processes, what happens if the queue is full and you use the put() method without a timeout?

Accepted Answer

It blocks indefinitely until a slot becomes available.. By default, put() is a blocking operation that will wait until a slot is available if the queue is full.

Answer

It restarts the child process.

Answer

It raises a Full exception immediately.

Answer

It silently drops the data.

Answer

It overwrites the oldest item in the queue.

Question 2

You are using the multiprocessing.Process class and notice that child processes are not terminating cleanly. Which method should you call to ensure the main process waits for the child process to complete?

Accepted Answer

process.join(). The join() method blocks the calling thread until the process whose join() method is called terminates.

Answer

process.wait()

Answer

process.terminate()

Answer

process.close()

Answer

process.is_alive()

Question 3

You are using the subprocess.run() function to execute an external command. Which argument ensures that the command's stdout is captured as a string rather than printed to the console?

Accepted Answer

capture_output=True. Setting capture_output=True automatically sets stdout and stderr to subprocess.PIPE.

Answer

text=True

Answer

stdout=True

Answer

shell=True

Answer

pipe=True

Answer

redirect=True

Question 4

Two threads are modifying a shared global integer. You want to ensure that only one thread modifies the integer at a time. Which synchronization primitive is most appropriate?

Accepted Answer

threading.Lock. A Lock (or Mutex) is the standard tool to ensure mutually exclusive access to a shared resource.

Answer

threading.Event

Answer

multiprocessing.Semaphore

Answer

multiprocessing.Queue

Answer

threading.Condition

Question 5

You are using a multiprocessing.Pool. Which method should you use to apply a function to a sequence of items and get the results back in order as they complete?

Accepted Answer

imap(). imap() returns an iterator that yields results in the order of the inputs.

Answer

apply()

Answer

map_async()

Answer

map()

Answer

starmap()

Question 6

What is the primary reason to use the multiprocessing module instead of the threading module for CPU-bound tasks in Python?

Accepted Answer

Multiprocessing bypasses the Global Interpreter Lock (GIL).. Because of the Global Interpreter Lock (GIL), multiple threads cannot execute Python bytecode simultaneously on multiple cores.

Answer

Threading cannot handle files.

Answer

Multiprocessing is faster for I/O.

Answer

Threading does not support locks.

Answer

Threading is deprecated.

Question 7

You are writing a Python script that needs to perform heavy I/O-bound tasks concurrently. Which module should you prioritize to minimize the overhead of global interpreter lock (GIL) contention?

Accepted Answer

threading. The threading module is ideal for I/O-bound tasks as it releases the GIL during blocking operations, whereas multiprocessing is better for CPU-bound tasks.

Answer

queue

Answer

subprocess

Answer

asyncio

Answer

multiprocessing

Question 8

When using subprocess.Popen, why is it dangerous to use shell=True with user-supplied input?

Accepted Answer

It leads to shell command injection vulnerabilities.. It introduces a command injection vulnerability where a user can execute arbitrary shell commands.

Answer

It prevents capturing stderr.

Answer

It slows down execution significantly.

Answer

It crashes the Python interpreter.

Answer

It forces the use of hardcoded paths.

Question 9

In the context of the threading module, what does the daemon flag do when set to True?

Accepted Answer

It causes the thread to exit when the main process exits.. Daemon threads exit automatically when the main program finishes.

Answer

It increases the thread's priority.

Answer

It prevents the thread from being interrupted.

Answer

It allows the thread to be killed by the OS.

Answer

It ensures the thread completes before the program exits.

Question 10

When spawning processes on Windows, what is the default start method used by the multiprocessing module?

Accepted Answer

spawn. The 'spawn' method is the default on Windows.

Answer

thread

Answer

exec

Answer

forkserver

Answer

fork

Question 11

Why should you use a 'with' statement when using a Lock?

Accepted Answer

It automatically handles lock acquisition and release.. It automatically acquires and releases the lock, ensuring it is released even if an exception occurs.

Answer

It allows multiple threads to acquire the lock.

Answer

It increases the performance of the lock.

Answer

It creates a thread-safe environment.

Answer

It prevents the lock from being garbage collected.

Question 12

You are managing subprocesses using subprocess.Popen. Which attribute of the Popen object should you check to verify the exit code after the process terminates?

Accepted Answer

returncode. The returncode attribute is populated after the process finishes or wait() is called.

Answer

code

Answer

status

Answer

poll()

Answer

exit_code

Question 13

You are using a multiprocessing.Semaphore(3). What happens when the 4th process attempts to acquire the semaphore?

Accepted Answer

It blocks until a slot is released.. The 4th process will block until one of the previous three processes releases the semaphore.

Answer

It creates a new process slot.

Answer

It raises an exception.

Answer

It bypasses the lock.

Answer

It is terminated by the OS.

Question 14

You have a thread waiting on a threading.Event. Which method should another thread call to wake up the waiting thread?

Accepted Answer

set(). The set() method sets the internal flag to true, causing wait() to return.

Answer

notify()

Answer

trigger()

Answer

start()

Answer

signal()

Question 15

Which object would you use to share a simple integer between processes that is safe for concurrent access?

Accepted Answer

multiprocessing.Value. multiprocessing.Value is designed specifically to share single values between processes with a lock.

Answer

list

Answer

threading.Lock

Answer

global variable

Answer

multiprocessing.Queue

Question 16

Which module allows you to run external programs and interact with their input/output streams?

Accepted Answer

subprocess. The subprocess module is the recommended way to spawn new processes and connect to their pipes.

Answer

sys

Answer

multiprocessing

Answer

os

Answer

threading

Question 17

Which of the following is true regarding daemon threads in Python?

Accepted Answer

They are abruptly terminated when the main process exits.. Daemon threads are terminated abruptly when the main program exits, which can lead to incomplete operations.

Answer

They are only used for system-level tasks.

Answer

They are guaranteed to finish before the program ends.

Answer

They use more memory than regular threads.

Answer

They cannot create child threads.

Question 18

You are using Pool.apply_async(). How do you retrieve the result of the function call?

Accepted Answer

Call the get() method on the returned object.. The apply_async method returns an AsyncResult object, and you must call the get() method on it.

Answer

Wait for the function to return.

Answer

Use the join() method on the pool.

Answer

Pass a callback function.

Answer

Check the pool's result list.

Question 19

If you want to run a function in a background thread, which class should you instantiate?

Accepted Answer

threading.Thread. The threading.Thread class is the standard way to create threads.

Answer

threading.Process

Answer

subprocess.Thread

Answer

multiprocessing.Thread

Answer

thread.Task

Question 20

What is the result of using a Pipe to communicate between two processes if both processes attempt to write to the same end simultaneously?

Accepted Answer

The data may be corrupted or interleaved.. Data corruption can occur as the messages may become interleaved or mangled.

Answer

It raises an exception.

Answer

The OS serializes the writes automatically.

Answer

The write blocks until the other finishes.

Answer

One of the writes is silently dropped.