PCPP2 Interprocess Communication — 15 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.

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It raises a Full exception immediately.

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It silently drops the data.

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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()

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process.terminate()

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process.close()

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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.

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text=True

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stdout=True

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shell=True

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pipe=True

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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

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multiprocessing.Queue

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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.

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apply()

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map_async()

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map()

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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.

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Threading cannot handle files.

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Multiprocessing is faster for I/O.

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Threading does not support locks.

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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

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subprocess

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asyncio

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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.

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It slows down execution significantly.

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It crashes the Python interpreter.

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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.

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It prevents the thread from being interrupted.

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It allows the thread to be killed by the OS.

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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

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exec

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forkserver

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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.

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It increases the performance of the lock.

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It creates a thread-safe environment.

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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

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status

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poll()

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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.

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It raises an exception.

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It bypasses the lock.

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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.

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notify()

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trigger()

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start()

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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

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threading.Lock

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global variable

Answer

multiprocessing.Queue