on Fri, 12 Dec 2025 12:30:20 +0800, Licay wrote: > 1. Avoid Parsing /proc > The current approach uses get_thread_state() to read /proc/$pid/status, > which isn't very reliable. > A better way would be to have waiterfn directly signal when it's ready > using atomic operations.
I haven't found a better way to check whether a process has entered the sleep state without using the proc interface for the time being. The kernel probably doesn't provide a system call to obtain whether a process has entered the sleep state. > 2. Use Atomic Counting Instead of Polling Thread State > Before entering futex_wait, waiterfn can atomically increment a counter. > The parent thread then just waits for this counter to reach the expected > value. > This is much simpler and avoids the overhead of checking /proc repeatedly. Using atomic instructions does not guarantee that the process is waiting in futex_wait. > 3. Use Standard Atomic Types > Replace the custom READ_ONCE/WRITE_ONCE macros with standard <stdatomic.h> > types like atomic_int. > It's cleaner and more portable across different platforms. Only two operations, atomic_set and atomic_read, are used here. Using WRITE_ONCE and READ_ONCE can avoid introducing too many dependencies. > Here's the basic idea: > - Add a global atomic_int ready_count variable > - In waiterfn: atomic_fetch_add(&ready_count, 1) right before futex_wait() > - Parent thread: spin-wait until atomic_load(&ready_count) reaches the > expected value Similarly, using atomic_inc before futex_wait does not guarantee that the thread has reached the futex_wait execution point. Thank you very much for your reply.
