'\" t
.\"     Title: struct futex_q
.\"    Author: 
.\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
.\"      Date: January 2017
.\"    Manual: Futex API reference
.\"    Source: Kernel Hackers Manual 4.8.15
.\"  Language: English
.\"
.TH "STRUCT FUTEX_Q" "9" "January 2017" "Kernel Hackers Manual 4\&.8\&." "Futex API reference"
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.SH "NAME"
struct_futex_q \- The hashed futex queue entry, one per waiting task
.SH "SYNOPSIS"
.sp
.nf
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;
};  
.fi
.SH "MEMBERS"
.PP
list
.RS 4
priority\-sorted list of tasks waiting on this futex
.RE
.PP
task
.RS 4
the task waiting on the futex
.RE
.PP
lock_ptr
.RS 4
the hash bucket lock
.RE
.PP
key
.RS 4
the key the futex is hashed on
.RE
.PP
pi_state
.RS 4
optional priority inheritance state
.RE
.PP
rt_waiter
.RS 4
rt_waiter storage for use with requeue_pi
.RE
.PP
requeue_pi_key
.RS 4
the requeue_pi target futex key
.RE
.PP
bitset
.RS 4
bitset for the optional bitmasked wakeup
.RE
.SH "DESCRIPTION"
.PP
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)\&.
.PP
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\&.
.PP
PI futexes are typically woken before they are removed from the hash list via the rt_mutex code\&. See
\fBunqueue_me_pi\fR\&.
.SH "AUTHOR"
.PP
\fBRusty Russell\fR <\&rusty@rustcorp.com.au\&>
.RS 4
Author.
.RE
.SH "COPYRIGHT"
.br