Bayyana locks, mutexes, critical sections, da semaphores.

Question

IT Interview Practice · Accepted Answer

**Mutex lock ne da ke tabbatar da mutual exclusion — thread ɗaya kawai zai iya riƙe shi ya shiga critical section da aka kare a lokaci ɗaya.** Semaphore yana faɗaɗa wannan don ba da damar har zuwa N masu riƙe a lokaci guda.

## Yadda yake aiki

- **Critical section**: yankin lambar da ke taɓa shared state kuma ba dole ya gudana concurrent ba.
- **Mutex (mutual exclusion)**: acquire kafin sashe, release bayan. Thread na biyu yana toshewa har sai ya zama kyauta. Yawanci thread mai acquire ne ke mallakarsa (shi kaɗai zai iya release).
- **Semaphore**: yana riƙe counter na permits N. `acquire()` yana ragewa (yana toshewa a 0), `release()` yana ƙarawa. Mutex a zahiri semaphore ne da N=1 amma da ownership semantics.

```python
lock = threading.Lock()
def transfer(a, b, amt):
    with lock:                 # critical section — one thread at a time
        a.balance -= amt
        b.balance += amt

# Semaphore: cap concurrent DB connections at 10
sem = threading.Semaphore(10)
def query():
    with sem:                  # up to 10 threads run this concurrently
        db.execute(...)
```

## Tarkuna

- **Manta release** → toshewa har abada. Yi amfani da `with`/RAII/`defer` domin release ya zama atomatik ko a lokacin exceptions.
- **Riƙe lock da yawa** yana kashe throughput; riƙe critical sections ƙanana.
- **Lock granularity**: coarse lock ɗaya mai sauƙi ne amma yana serialize komai; fine locks da yawa suna scale sosai amma suna haɗarin deadlock.

## Me ya sa yake da muhimmanci

Waɗannan su ne kayan aiki na yau da kullum don kare shared state. Mutexes suna serialize shiga don hana races; semaphores suna ƙuntata resource pool (connections, permits, rate limits). Zaɓen primitive da ya dace da riƙe critical sections ƙanana shine bambanci tsakanin daidai-da-sauri da daidai-amma-jinkiri.

Yadda yake aiki

Tarkuna

Me ya sa yake da muhimmanci

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