pthread_join() Implementation Analysis: Understanding Linux Thread Synchronization Mechanisms

This article analyzes the pthread_join() function implementation, comparing the different approaches used by glibc and musl C libraries in Linux environments.

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Introduction

The author participated in the 2025 National Computer System Capability Competition - Operating System Design competition. During the process of implementing threading mechanisms, I gained insights into pthread library implementations in both glibc and musl. This article shares my research findings on pthread_join() implementation.

In multithreaded programming, the pthread_join() function is used to wait for a specified thread to terminate. Its implementation mechanisms differ significantly between GLIBC and MUSL C libraries. This article examines the specific working principles of pthread_join() in Linux environments.

Key Points

• GLIBC implementation uses kernel-assisted synchronization with CLONE_CHILD_CLEARTID flags
• MUSL implementation relies on user-space state management with detach_state fields
• Both approaches use futex() system calls but with different strategies
• Analysis includes strace output examination and source code exploration