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This article provides a comprehensive overview of Linux thread synchronization, explaining core concepts such as mutexes, condition variables, semaphores, and futexes, describing their implementation details, code examples, and common usage scenarios like producer‑consumer and reader‑writer problems.
Linux futexes provide a fast userspace lock backed by a kernel wait queue, using atomic operations when uncontended and system calls such as FUTEX_WAIT, FUTEX_WAKE, and priority‑inheritance variants to manage contention, requeueing, and priority inversion via rt‑mutex structures.
The article explains Android’s user‑space locking hierarchy—from Java intrinsic and JUC locks to C++ std::mutex and pthread mutexes—detailing their internal structures, state transitions, and reliance on futex system calls for kernel‑level blocking, helping developers optimize synchronization across Java and native layers.
A detailed investigation reveals that a futex bug in Linux kernel 2.6.32-504 causes Java programs on Hadoop and xtrabackup processes to hang, and the issue can be resolved by upgrading to a newer kernel version.