1.\" 2.\" Copyright (c) 1996 Joerg Wunsch 3.\" 4.\" All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 15.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR 16.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 17.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 18.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT, 19.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 20.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 21.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 22.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 23.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 24.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 25.\" 26.\" $FreeBSD$ 27.\" 28.Dd December 17, 1998 29.Os 30.Dt SLEEP 9 31.Sh NAME 32.Nm sleep , 33.Nm msleep , 34.Nm tsleep , 35.Nm wakeup 36.Nd wait for events 37.Sh SYNOPSIS 38.In sys/param.h 39.In sys/systm.h 40.In sys/proc.h 41.Ft int 42.Fn tsleep "void *ident" "int priority" "const char *wmesg" "int timo" 43.Ft int 44.Fn msleep "void *ident" "struct mtx *mtx" "int priority" "const char *wmesg" "int timo" 45.Ft void 46.Fn wakeup "void *ident" 47.Ft void 48.Fn wakeup_one "void *ident" 49.Sh DESCRIPTION 50The functions 51.Fn tsleep 52and 53.Fn wakeup 54handle event-based process blocking. 55If a process must wait for an 56external event, it is put on sleep by 57.Fn tsleep . 58The parameter 59.Fa ident 60is an arbitrary address that uniquely identifies the event on which 61the process is being asleep. 62All processes sleeping on a single 63.Fa ident 64are woken up later by 65.Fn wakeup , 66often called from inside an interrupt routine, to indicate that the 67resource the process was blocking on is available now. 68.Pp 69The parameter 70.Fa wmesg 71is a string describing the sleep condition for tools like 72.Xr ps 1 . 73Due to the limited space of those programs to display arbitrary strings, 74this message should not be longer than 6 characters. 75.Pp 76The 77.Fn wakeup_one 78function is used to make the first process in the queue that is 79sleeping on the parameter 80.Fa ident 81runnable. 82This can prevent the system from becoming saturated 83when a large number of processes are sleeping on the same address, 84but only one of them can actually do any useful work when made 85runnable. 86.Pp 87The 88.Fn tsleep 89function is the general sleep call. 90Suspends the current process until a wakeup is 91performed on the specified identifier. 92The process will then be made 93runnable with the specified 94.Fa priority . 95Sleeps at most 96.Fa timo 97\&/ hz seconds (0 means no timeout). 98If the 99.Va Giant 100lock is not held, then 101.Fa timo 102must be non-zero. 103If 104.Fa priority 105includes the 106.Dv PCATCH 107flag, signals are checked before and after sleeping, else signals are 108not checked. 109Returns 0 if awakened, 110.Er EWOULDBLOCK 111if the timeout expires. 112If 113.Dv PCATCH 114is set and a signal needs to be delivered, 115.Er ERESTART 116is returned if the current system call should be restarted if 117possible, and 118.Er EINTR 119is returned if the system call should be interrupted by the signal 120(return 121.Er EINTR ) . 122.Pp 123The 124.Fn msleep 125function is a variation on tsleep. 126The parameter 127.Fa mtx 128is a mutex which will be released before sleeping and reacquired before 129.Fn msleep 130returns. 131If 132.Fa priority 133includes the 134.Dv PDROP 135flag, the 136.Fa mtx 137parameter will not be reacquired before returning. 138The mutex is 139used to ensure that a condition can be checked atomically, and 140that the current process can be suspended without missing a 141change to the condition, or an associated wakeup. 142.Sh RETURN VALUES 143See above. 144.Sh SEE ALSO 145.Xr ps 1 , 146.Xr malloc 9 , 147.Xr mi_switch 9 148.Sh HISTORY 149The sleep/wakeup process synchronization mechanism is very old. 150It 151appeared in a very early version of 152.Ux . 153.Pp 154The 155.Fn tsleep 156function appeared in 157.Bx 4.4 . 158.Pp 159The 160.Fn sleep 161function used to be the traditional form. 162It did not let you specify a timeout or a 163.Fa wmesg , 164hence it was discontinued. 165.Sh AUTHORS 166.An -nosplit 167This man page was written by 168.An J\(:org Wunsch Aq joerg@FreeBSD.org . 169