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. 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26.\" $FreeBSD$ 27.\" 28.Dd December 17, 1998 29.Os 30.Dt SLEEP 9 31.Sh NAME 32.Nm msleep , 33.Nm msleep_spin , 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 *chan" "int priority" "const char *wmesg" "int timo" 43.Ft int 44.Fn msleep "void *chan" "struct mtx *mtx" "int priority" "const char *wmesg" "int timo" 45.Ft int 46.Fn msleep_spin "void *chan" "struct mtx *mtx" "const char *wmesg" "int timo" 47.Ft void 48.Fn wakeup "void *chan" 49.Ft void 50.Fn wakeup_one "void *chan" 51.Sh DESCRIPTION 52The functions 53.Fn tsleep 54and 55.Fn wakeup 56handle event-based process blocking. 57If a process must wait for an 58external event, it is put on sleep by 59.Fn tsleep . 60The parameter 61.Fa chan 62is an arbitrary address that uniquely identifies the event on which 63the process is being asleep. 64All processes sleeping on a single 65.Fa chan 66are woken up later by 67.Fn wakeup , 68often called from inside an interrupt routine, to indicate that the 69resource the process was blocking on is available now. 70.Pp 71The parameter 72.Fa wmesg 73is a string describing the sleep condition for tools like 74.Xr ps 1 . 75Due to the limited space of those programs to display arbitrary strings, 76this message should not be longer than 6 characters. 77.Pp 78The 79.Fn wakeup_one 80function is used to make the first process in the queue that is 81sleeping on the parameter 82.Fa chan 83runnable. 84This can prevent the system from becoming saturated 85when a large number of processes are sleeping on the same address, 86but only one of them can actually do any useful work when made 87runnable. 88.Pp 89The 90.Fn tsleep 91function is the general sleep call. 92Suspends the current process until a wakeup is 93performed on the specified identifier. 94The process will then be made 95runnable with the specified 96.Fa priority . 97Sleeps at most 98.Fa timo 99\&/ hz seconds (0 means no timeout). 100If the 101.Va Giant 102lock is not held and 103.Fa mtx 104is 105.Dv NULL , 106then 107.Fa timo 108must be non-zero. 109If 110.Fa priority 111includes the 112.Dv PCATCH 113flag, signals are checked before and after sleeping, otherwise signals are 114not checked. 115Returns 0 if awakened, 116.Er EWOULDBLOCK 117if the timeout expires. 118If 119.Dv PCATCH 120is set and a signal needs to be delivered, 121.Er ERESTART 122is returned if the current system call should be restarted if 123possible, and 124.Er EINTR 125is returned if the system call should be interrupted by the signal 126(return 127.Er EINTR ) . 128.Pp 129The 130.Fn msleep 131function is a variation on tsleep. 132The parameter 133.Fa mtx 134is a mutex which will be released before sleeping and reacquired before 135.Fn msleep 136returns. 137If 138.Fa priority 139includes the 140.Dv PDROP 141flag, the 142.Fa mtx 143parameter will not be reacquired before returning. 144The mutex is 145used to ensure that a condition can be checked atomically, and 146that the current process can be suspended without missing a 147change to the condition, or an associated wakeup. 148.Pp 149The 150.Fn msleep_spin 151function is another variation on 152.Fn tsleep 153similar to 154.Fn msleep . 155Unlike 156.Fn msleep , 157this function accepts a spin mutex rather than a default mutex for its 158.Fa mtx 159parameter. 160It is also more limited in that it does not accept a 161.Fa priority 162parameter. 163Thus, it will not change the priority of a sleeping thread, 164and it does not support the 165.Dv PDROP 166and 167.Dv PCATCH 168flags. 169.Sh RETURN VALUES 170See above. 171.Sh SEE ALSO 172.Xr ps 1 , 173.Xr malloc 9 , 174.Xr mi_switch 9 175.Sh HISTORY 176The sleep/wakeup process synchronization mechanism is very old. 177It 178appeared in a very early version of 179.Ux . 180.Pp 181The 182.Fn tsleep 183function appeared in 184.Bx 4.4 . 185The 186.Fn msleep 187function appeared in 188.Fx 5.0 , 189and the 190.Fn msleep_spin 191function appeared in 192.Fx 7.0 . 193.Pp 194The 195.Fn sleep 196function used to be the traditional form. 197It did not let you specify a timeout or a 198.Fa wmesg , 199hence it was discontinued. 200.Sh AUTHORS 201.An -nosplit 202This manual page was written by 203.An J\(:org Wunsch Aq joerg@FreeBSD.org . 204