STRUCT FUTEX_Q(9)                      Futex API reference                      STRUCT FUTEX_Q(9)



NAME
       struct_futex_q - The hashed futex queue entry, one per waiting task

SYNOPSIS
       struct futex_q {
         struct plist_node list;
         struct task_struct * task;
         spinlock_t * lock_ptr;
         union futex_key key;
         struct futex_pi_state * pi_state;
         struct rt_mutex_waiter * rt_waiter;
         union futex_key * requeue_pi_key;
         u32 bitset;
       };

MEMBERS
       list
           priority-sorted list of tasks waiting on this futex

       task
           the task waiting on the futex

       lock_ptr
           the hash bucket lock

       key
           the key the futex is hashed on

       pi_state
           optional priority inheritance state

       rt_waiter
           rt_waiter storage for use with requeue_pi

       requeue_pi_key
           the requeue_pi target futex key

       bitset
           bitset for the optional bitmasked wakeup

DESCRIPTION
       We use this hashed waitqueue, instead of a normal wait_queue_t, so we can wake only the
       relevant ones (hashed queues may be shared).

       A futex_q has a woken state, just like tasks have TASK_RUNNING. It is considered woken
       when plist_node_empty(q->list) || q->lock_ptr == 0. The order of wakeup is always to make
       the first condition true, then the second.

       PI futexes are typically woken before they are removed from the hash list via the rt_mutex
       code. See unqueue_me_pi.

AUTHOR
       Rusty Russell <rusty AT rustcorp.au>
           Author.

COPYRIGHT
Kernel Hackers Manual 4.8.                 January 2017                         STRUCT FUTEX_Q(9)