1.\" $NetBSD: _lwp_park.2,v 1.7 2008/04/30 13:10:51 martin Exp $ 2.\" 3.\" Copyright (c) 2003, 2007 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Jason R. Thorpe of Wasabi Systems, Inc, and by Andrew Doran. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd September 25, 2007 31.Dt _LWP_PARK 2 32.Os 33.Sh NAME 34.Nm _lwp_park 35.Nd wait interruptably in the kernel 36.Sh LIBRARY 37.Lb libc 38.Sh SYNOPSIS 39.In lwp.h 40.Ft int 41.Fn _lwp_park "const struct timespec *abstime" "lwpid_t unpark" "const void *hint" "const void *unparkhint" 42.Sh DESCRIPTION 43.Fn _lwp_park 44can be used to synchronize access to resources among multiple light-weight 45processes. 46It causes the calling LWP to wait interruptably in the kernel, until one 47of the following conditions is met: 48.Bl -bullet 49.It 50The 51.Fa abstime 52argument is non-NULL, and the absolute UTC time it specifies has passed. 53.It 54The LWP receives a directed signal posted using 55.Fn _lwp_kill , 56or is elected to handle a signal on behalf of its containing process. 57.It 58The LWP is awoken by another LWP in the same process that has made 59a call to 60.Fn _lwp_wakeup . 61.It 62The LWP is awoken by another LWP in the same process that has made 63a call to 64.Fn _lwp_unpark 65or 66.Fn _lwp_unpark_all . 67.El 68.Pp 69The preferred method to awaken an LWP sleeping as a result of a call 70to 71.Fn _lwp_park 72is to make a call to 73.Fn _lwp_unpark , 74or 75.Fn _lwp_unpark_all . 76The 77.Fn _lwp_wakeup 78system call is a more general facility, and requires more resources 79to execute. 80.Pp 81The optional 82.Fa hint 83argument specifies the address of object upon which the LWP is 84synchronizing. 85When the 86.Fa hint 87value is matched between calls to 88.Fn _lwp_park 89and 90.Fn _lwp_unpark 91or 92.Fn _lwp_unpark_all , 93it may reduce the time necessary for the system to resume execution 94of waiting LWPs. 95.Pp 96The 97.Fa unpark 98and 99.Fa unparkhint 100arguments can be used to fold a park operation and unpark operation into a 101single system call. 102If 103.Fa unpark 104is non-zero, the system will behave as if the following call had been made 105before the calling thread begins to wait: 106.Bd -literal 107 _lwp_unpark(unpark, unparkhint); 108.Ed 109.Sh RETURN VALUES 110.Fn _lwp_park 111may return a value of 0. 112Otherwise, \-1 is returned and 113.Va errno 114is set to provide more information. 115.Sh ERRORS 116.Bl -tag -width [EINVAL] 117.It Bq Er EALREADY 118A request was made to wake the LWP before it began to wait in 119the kernel. 120.It Bq Er EINTR 121The LWP has been awoken by a signal or by a call to one of the 122following functions: 123.Fn _lwp_unpark , 124.Fn _lwp_unpark_all , 125.Fn _lwp_wakeup . 126.It Bq Er EINVAL 127The time value specified by 128.Fa abstime 129is invalid. 130.It Bq Er ESRCH 131No LWP can be found in the current process corresponding to 132.Fa unpark . 133.It Bq Er ETIMEDOUT 134The UTC time specified by 135.Fa abstime 136has passed. 137.El 138.Sh SEE ALSO 139.Xr _lwp_unpark 2 , 140.Xr _lwp_unpark_all 2 , 141.Xr _lwp_wakeup 2 142.Sh HISTORY 143The 144.Fn _lwp_park 145system call first appeared in 146.Nx 5.0 . 147