cppAsync race conditionMedium

Missing lock_guard unlocks mutex prematurely

Time: 0:00

BugFind the bug and fix the code

What it should do

Safely increment shared counter with mutex. Example: safeIncrementSharedCounter(5) -> 6

What happens instead

Early return leaves mutex unlocked or unprotected race on exception

#include <iostream>
#include <mutex>

std::mutex mtx;
int counter = 0;

int safeIncrementSharedCounter(int initial) {
    counter = initial;
    mtx.lock();
    if (initial < 0) {
        // Missing unlock on early exit branch!
        return -1;
    }
    counter += 1;
    mtx.unlock();
    return counter;
}

int main() {
    std::cout << safeIncrementSharedCounter(5) << std::endl;
    return 0;
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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Hints

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Hint 2

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Hint 3

Unlocks after Hint 2

This bug belongs to the async and race conditions pattern

A missing await, unbuffered channel deadlocks, ConcurrentModificationException, and data races under load.

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#include <iostream> #include <mutex> std::mutex mtx; int counter = 0; int safeIncrementSharedCounter(int initial) { counter = initial; mtx.lock(); if (initial < 0) { // Missing unlock on early exit branch! return -1; } counter += 1; mtx.unlock(); return counter; } int main() { std::cout << safeIncrementSharedCounter(5) << std::endl; return 0; }

Missing lock_guard unlocks mutex prematurely

What it should do

What happens instead

More async and race conditions to practise

Missing lock_guard unlocks mutex prematurely

What it should do

What happens instead

More async and race conditions to practise