---
title: Uninitialized mutexes
framework: xcode
role: article
role_heading: Article
path: xcode/uninitialized-mutexes
---

# Uninitialized mutexes

Detects when you use an uninitialized mutex.

## Overview

Overview Use this check to detect when you call pthread_mutex_lock(_:) or pthread_mutex_unlock(_:) with an uninitialized pthread_mutex_t variable. Attempting to use an uninitialized mutex results in an error, and bypasses ordering conditions that exist on a locked mutex. Available in Xcode 8 and later. Use of uninitialized mutex in C In the following example, the pthread_mutex_lock(_:) function executes with an uninitialized pthread_mutex_t variable: static pthread_mutex_t mutex; void performWork() {     pthread_mutex_lock(&mutex); // Error: uninitialized mutex     // ...     pthread_mutex_unlock(&mutex); } Solution Use the pthread_once(_:_:) function to initialize a mutex before you use it. static pthread_once_t once = PTHREAD_ONCE_INIT; static pthread_mutex_t mutex; void init() {         pthread_mutex_init(&mutex, NULL); } void performWork() {     pthread_once(&once, init); // Correct     pthread_mutex_lock(&mutex);     // ...     pthread_mutex_unlock(&mutex); }

## See Also

### Thread Sanitizer

- [Data races](xcode/data-races.md)
- [Swift access races](xcode/swift-access-races.md)
- [Races on collections and other APIs](xcode/races-on-collections-and-other-apis.md)
- [Thread leaks](xcode/thread-leaks.md)