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futex.2: Minor wording fixes 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-07-28 11:09:15 +02:00
parent 55f9e85ead
commit fd1056148b
1 changed files with 16 additions and 12 deletions
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28
man2/futex.2
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@ -249,15 +249,18 @@ futex word pointed to by the address
.I uaddr
still contains the expected value
.IR val ,
and if so, then sleeps awaiting
and if so, then sleeps waiting for a
.B FUTEX_WAKE
on the futex word.
operation on the futex word.
The load of the value of the futex word is an atomic memory
access (i.e., using atomic machine instructions of the respective
architecture).
This load, the comparison with the expected value, and
starting to sleep are performed atomically and totally ordered with respect
to other futex operations on the same futex word.
starting to sleep are performed atomically
.\" FIXME: Torvald, what do you mean by "totally odered" here?
.\" (Also used at various other points in the page.)
and totally ordered
with respect to other futex operations on the same futex word.
If the thread starts to sleep,
it is considered a waiter on this futex word.
If the futex value does not match
@ -266,7 +269,8 @@ then the call fails immediately with the error
.BR EAGAIN .
The purpose of the comparison with the expected value is to prevent lost
wake-ups: If another thread changed the value of the futex word after the
wake-ups.
If another thread changed the value of the futex word after the
calling thread decided to block based on the prior value,
and if the other thread executed a
.BR FUTEX_WAKE
@ -809,10 +813,10 @@ Note that a PI futex word never just has the value
which is a permissible state for non-PI futexes.
With this policy in place,
a user-space application can acquire a not-acquired
a user-space application can acquire an unacquired
lock or release a lock that no other threads try to acquire using atomic
instructions executed in user space (e.g., a compare-and-swap operation
such as
instructions executed in user mode
(e.g., a compare-and-swap operation such as
.I cmpxchg
on the x86 architecture).
Acquiring a lock simply consists of using compare-and-swap to atomically
@ -845,8 +849,8 @@ before the calling thread returns to user space.
It is important to note
.\" FIXME We need some explanation in the following paragraph of *why*
.\" it is important to note that "the kernel will update the
.\" futex word's value prior
to returning to user space" . Can someone explain?
.\" futex word's value prior to returning to user space".
.\" Can someone explain?
that the kernel will update the futex word's value prior
to returning to user space.
Unlike the other futex operations described above,
@ -879,7 +883,7 @@ PI futexes are operated on by specifying one of the following values in
.\" errors.
.\"
This operation is used after after an attempt to acquire
the lock via an atomic user-space instruction failed
the lock via an atomic user-mode instruction failed
because the futex word has a nonzero value\(emspecifically,
because it contained the namespace-specific TID of the lock owner.
.\" FIXME In the preceding line, what does "namespace-specific" mean?
@ -1179,7 +1183,7 @@ requeued to the futex for the futex word at
.IR uaddr2 .
If this value is greater than
.IR val ,
then difference is the number of waiters requeued to the futex for the
then the difference is the number of waiters requeued to the futex for the
futex word at
.IR uaddr2 .
.TP