The article discusses the performance of mutex implementations across different operating systems, particularly focusing on the Cosmopolitan Libc library. This library is notable for its ability to create polyglot binaries that can run on multiple operating systems, including AMD64 and ARM64 architectures. The author aims to demonstrate that Cosmopolitan's mutex library is not only versatile but also highly efficient for production workloads. To illustrate the performance of various mutex implementations, the author conducts a benchmark test involving 30 threads that increment a shared integer 100,000 times. This scenario is designed to highlight the performance differences in heavily contended situations, where multiple threads compete for access to the same resource. The benchmark results reveal that Cosmopolitan's mutexes significantly outperform other implementations. On Windows, Cosmopolitan's pthread_mutex_t is 2.75 times faster than Microsoft's SRWLOCK, which was previously considered the best option. The results show that Cosmopolitan mutexes consume 18 times fewer CPU resources compared to SRWLOCK and are 65 times faster than Cygwin's pthread_mutex_t. In the Linux environment, Cosmopolitan mutexes again excel, being three times faster than glibc's pthread_mutex_t and 11 times faster than musl libc's implementation. The author emphasizes that Cosmopolitan's mutexes allow for more efficient CPU usage, which is crucial for servers running multiple jobs. On macOS, the results are slightly different, with Apple's Libc outperforming Cosmopolitan's mutexes. The author speculates that this may be due to the close integration of the M2 processor with the XNU operating system, leading to a simpler mutex algorithm in Cosmopolitan that relies on system calls. The article also delves into the technical aspects of how Cosmopolitan mutexes achieve their performance. The author credits the use of a library called nsync, developed by Mike Burrows, which employs several advanced techniques. These include an optimistic compare-and-swap (CAS) approach for quick locking, a doubly linked list of waiters to manage contention, and the use of futexes to minimize CPU usage when threads are waiting for a lock. The author shares insights into the design choices made in nsync, such as avoiding starvation and implementing a "designated waker" mechanism to efficiently manage thread wake-ups. The article concludes with a call to action for readers to explore the source code and consider the implications of using Cosmopolitan Libc in their own projects. Overall, the benchmarks and technical analysis presented in the article highlight the advantages of Cosmopolitan's mutex library, positioning it as a strong contender for developers seeking efficient and effective solutions for multithreaded programming across various operating systems. The author expresses a sense of urgency for adopting this library in production environments, given its potential to optimize resource usage and improve performance.