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futex.2: Elaborate on the operation of FUTEX_WAIT 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2015-01-12 14:01:22 +01:00
parent 36448cfa8d
commit f065673c7a
1 changed files with 27 additions and 6 deletions
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33
man2/futex.2
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@ -152,13 +152,26 @@ is one of the following:
.TP
.BR FUTEX_WAIT " (since Linux 2.6.0)"
.\" Strictly speaking, since some time in 2.5.x
This operation atomically verifies that the futex address
This operation tests that the value at the
location pointed to by the futex address
.I uaddr
still contains the value
.IR val ,
and sleeps awaiting
and then sleeps awaiting
.B FUTEX_WAKE
on this futex address.
on the futex address.
The test and sleep steps are performed atomically.
If the futex value does not match
.IR val ,
then the call returns immediately with the error
.BR EWOULDBLOCK .
.\" FIXME I added the following sentence. Please confirm that it is correct.
The purpose of the test step is to detect races where
another process changes that value of the futex between
the time it was last checked and the time of the
.BR FUTEX_WAIT
oepration.
If the
.I timeout
@ -195,9 +208,17 @@ operation.
.TP
.BR FUTEX_WAKE " (since Linux 2.6.0)"
.\" Strictly speaking, since Linux 2.5.x
This operation wakes at most \fIval\fP
processes waiting on this futex address (i.e., inside
.BR FUTEX_WAIT ).
This operation wakes at most
.I val
processes waiting (i.e., inside
.BR FUTEX_WAIT )
on the futex at the address
.IR uaddr .
Most commonly,
.I val
is specified as either 1 (wake up a single waiter) or
.BR INT_MAX
(wake up all waiters).
The arguments
.IR timeout ,