3d265fce43
- skipping paragraph macro: Pp after Sh - sections out of conventional order: Sh EXAMPLES - whitespace at end of input line - normalizing date format
196 lines
4.9 KiB
Groff
196 lines
4.9 KiB
Groff
.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)getitimer.2 8.3 (Berkeley) 5/16/95
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.\" $FreeBSD$
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.\"
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.Dd May 1, 2020
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.Dt GETITIMER 2
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.Os
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.Sh NAME
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.Nm getitimer ,
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.Nm setitimer
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.Nd get/set value of interval timer
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/time.h
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.Fd "#define ITIMER_REAL 0"
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.Fd "#define ITIMER_VIRTUAL 1"
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.Fd "#define ITIMER_PROF 2"
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.Ft int
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.Fn getitimer "int which" "struct itimerval *value"
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.Ft int
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.Fn setitimer "int which" "const struct itimerval *value" "struct itimerval *ovalue"
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.Sh DESCRIPTION
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The system provides each process with three interval timers,
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defined in
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.In sys/time.h .
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The
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.Fn getitimer
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system call returns the current value for the timer specified in
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.Fa which
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in the structure at
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.Fa value .
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The
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.Fn setitimer
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system call sets a timer to the specified
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.Fa value
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(returning the previous value of the timer if
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.Fa ovalue
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is not a null pointer).
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.Pp
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A timer value is defined by the
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.Fa itimerval
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structure:
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.Bd -literal -offset indent
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struct itimerval {
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struct timeval it_interval; /* timer interval */
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struct timeval it_value; /* current value */
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};
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.Ed
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.Pp
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If
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.Fa it_value
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is non-zero, it indicates the time to the next timer expiration.
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If
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.Fa it_interval
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is non-zero, it specifies a value to be used in reloading
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.Fa it_value
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when the timer expires.
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Setting
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.Fa it_value
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to 0 disables a timer, regardless of the value of
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.Fa it_interval .
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Setting
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.Fa it_interval
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to 0 causes a timer to be disabled after its next expiration (assuming
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.Fa it_value
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is non-zero).
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.Pp
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Time values smaller than the resolution of the
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system clock are rounded up to this resolution
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(typically 10 milliseconds).
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.Pp
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The
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.Dv ITIMER_REAL
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timer decrements in real time.
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A
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.Dv SIGALRM
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signal is
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delivered when this timer expires.
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.Pp
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The
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.Dv ITIMER_VIRTUAL
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timer decrements in process virtual time.
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It runs only when the process is executing.
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A
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.Dv SIGVTALRM
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signal
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is delivered when it expires.
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.Pp
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The
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.Dv ITIMER_PROF
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timer decrements both in process virtual time and
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when the system is running on behalf of the process.
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It is designed
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to be used by interpreters in statistically profiling the execution
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of interpreted programs.
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Each time the
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.Dv ITIMER_PROF
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timer expires, the
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.Dv SIGPROF
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signal is
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delivered.
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Because this signal may interrupt in-progress
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system calls, programs using this timer must be prepared to
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restart interrupted system calls.
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.Pp
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The maximum number of seconds allowed for
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.Fa it_interval
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and
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.Fa it_value
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in
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.Fn setitimer
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is 100000000.
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.Sh NOTES
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Three macros for manipulating time values are defined in
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.In sys/time.h .
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The
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.Fn timerclear
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macro
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sets a time value to zero,
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.Fn timerisset
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tests if a time value is non-zero, and
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.Fn timercmp
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compares two time values.
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.Sh RETURN VALUES
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.Rv -std
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.Sh ERRORS
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The
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.Fn getitimer
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and
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.Fn setitimer
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system calls
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EFAULT
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The
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.Fa value
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argument specified a bad address.
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.It Bq Er EINVAL
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The
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.Fa value
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argument specified a time that was too large
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to be handled.
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.El
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.Sh SEE ALSO
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.Xr gettimeofday 2 ,
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.Xr select 2 ,
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.Xr sigaction 2 ,
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.Xr clocks 7
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.Sh STANDARDS
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The
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.Fn getitimer
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and
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.Fn setitimer
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functions conform to
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.St -p1003.1-2001 .
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The later
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.St -p1003.1-2008
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revision however marked both functions as obsolescent,
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recommending the use of
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.Xr timer_gettime 2
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and
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.Xr timer_settime 2
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instead.
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.Sh HISTORY
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The
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.Fn getitimer
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system call appeared in
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.Bx 4.2 .
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