[Bug] Mutex leak in delete_current() when exception thrown under CONSISTENCY_CHECKING

[hanqing2025]

Describe the Bug

A mutex leak in delete_current() causes permanent deadlock when an exception is thrown while holding the lock. When compiled with CONSISTENCY_CHECKING defined, the function acquires a mutex but throws std::runtime_error without releasing it.

Location: src/prioque.cpp (lines 355-386)

void delete_current(Queue * q)
{
    Queue_element temp, prev;

    // lock entire queue
    pthread_mutex_lock(&(q->lock));  // Line 355: Lock acquired

#if defined(CONSISTENCY_CHECKING)
    if(q->queue == 0 || q->current == 0) {
        std::string msg("Null pointer in function delete_current()\n");
        fprintf(stderr, "%s", msg.c_str());
        throw std::runtime_error(msg);  // Line 361: BUG - exception with lock held!
    }
    else
#endif
    {
        // ... deletion logic ...
        free(q->current->info);
        q->current->info = NULL;
        temp = q->current;
        // ... more deletion logic ...
        free(temp);
        (q->queuelength)--;
    }

    nolock_rewind_queue(q);

    // release lock on queue
    pthread_mutex_unlock(&(q->lock));  // Line 386: Never reached on exception
}

Impact:

• Queue mutex q->lock remains permanently locked when exception is thrown
• All subsequent queue operations block permanently
• File carving operations completely stall → Denial of Service

Execution Flow:

Thread 1:
  → pthread_mutex_lock(&(q->lock))       // Lock acquired
  → Check: q->queue == 0 || q->current == 0  // Condition TRUE
  → throw std::runtime_error(msg)        // Exception thrown
  → pthread_mutex_unlock() SKIPPED       // BUG: lock never released
  → q->lock remains locked forever

Thread 2, 3, ...N:
  → pthread_mutex_lock(&(q->lock))       // BLOCKS permanently
  → Complete deadlock state

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I would appreciate it if you could review and confirm this potential issue. Thank you for your time and for maintaining this project!