futex (nr 202)

Linux Signature

long futex(uint32_t *uaddr, int futex_op, uint32_t val,
           const struct timespec *timeout, uint32_t *uaddr2, uint32_t val3);

Description

Provides fast user-space locking primitives. FUTEX_WAIT blocks the calling thread until the value at uaddr changes; FUTEX_WAKE wakes threads waiting on uaddr.

Current Implementation

Always returns 0 (success). Each process is single-threaded, so musl’s internal locks (used by stdio, malloc, etc.) are never contended. The FUTEX_WAIT path is never reached in practice, and FUTEX_WAKE returning 0 (no waiters woken) is correct.

Source: osl/src/syscalls/mod.rs — inline stub in syscall_dispatch

Future Work

• Implement FUTEX_WAIT and FUTEX_WAKE properly once multi-threaded user processes are supported.
• Support FUTEX_WAIT_BITSET and other operations used by musl’s condition variables.