Lock
- Python course
- Expert
- Lesson 32/47
- 5 min
Learn critical sections with threading.Lock.
What is threading.Lock?
threading.Lock ensures only one thread at a time accesses a shared resource. .acquire() takes the lock and .release() frees it.
A critical section is a code region where multiple threads write to the same resource. Without a lock two threads may write simultaneously and cause a race condition. With Lock you protect this region: the first thread acquires, and others wait until it releases. This is the fundamental safety tool of threaded programming.
Using with Lock
The with lock: block automatically takes and frees the lock. It is safer than writing acquire/release; even if an exception occurs the lock is freed automatically.
This pattern is known as a context manager. Entering the block calls acquire; leaving calls release. Forgetting to unlock is a common mistake; with prevents it. Production code should always prefer with lock:.
Practice Critical section with Lock
Import with from threading import Lock. Create a lock with lock = Lock(). Call lock.acquire(), do print("kritik"), call lock.release().
Starter code
# create a lock
# protect the critical section
# printSample solution
from threading import Lock
lock = Lock()
lock.acquire()
print("critical")
lock.release()Expected output
kritik
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does Lock.acquire do?
lock = Lock()
lock.acquire()
# critical section
lock.release()- Returns the lock state
- Deletes the lock
- Releases the lock
- Takes the lock, waits if held Correct answer
Explanation: acquire takes the lock; if another thread holds it, it waits.
2 Complete the acquire call
lock = Lock()
lock.____()
print("kritik")
lock.release()lock = Lock()
lock.acquire()
print("kritik")
lock.release()Explanation: acquire() takes the lock.
3 Match Lock concepts
| Term | Meaning |
|---|---|
Lock |
Lock object |
acquire |
Takes the lock |
release |
Frees the lock |
critical section |
Protected code |