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, then 103.Fa timo 104must be non-zero. 105If 106.Fa priority 107includes the 108.Dv PCATCH 109flag, signals are checked before and after sleeping, otherwise signals are 110not checked. 111Returns 0 if awakened, 112.Er EWOULDBLOCK 113if the timeout expires. 114If 115.Dv PCATCH 116is set and a signal needs to be delivered, 117.Er ERESTART 118is returned if the current system call should be restarted if 119possible, and 120.Er EINTR 121is returned if the system call should be interrupted by the signal 122(return 123.Er EINTR ) . 124.Pp 125The 126.Fn msleep 127function is a variation on tsleep. 128The parameter 129.Fa mtx 130is a mutex which will be released before sleeping and reacquired before 131.Fn msleep 132returns. 133If 134.Fa priority 135includes the 136.Dv PDROP 137flag, the 138.Fa mtx 139parameter will not be reacquired before returning. 140The mutex is 141used to ensure that a condition can be checked atomically, and 142that the current process can be suspended without missing a 143change to the condition, or an associated wakeup. 144.Pp 145The 146.Fn msleep_spin 147function is another variation on 148.Fn tsleep 149similar to 150.Fn msleep . 151Unlike 152.Fn msleep , 153this function accepts a spin mutex rather than a default mutex for its 154.Fa mtx 155parameter. 156It is also more limited in that it does not accept a 157.Fa priority 158parameter. 159Thus, it will not change the priority of a sleeping thread, 160and it does not support the 161.Dv PDROP 162and 163.Dv PCATCH 164flags. 165.Sh RETURN VALUES 166See above. 167.Sh SEE ALSO 168.Xr ps 1 , 169.Xr malloc 9 , 170.Xr mi_switch 9 171.Sh HISTORY 172The sleep/wakeup process synchronization mechanism is very old. 173It 174appeared in a very early version of 175.Ux . 176.Pp 177The 178.Fn tsleep 179function appeared in 180.Bx 4.4 . 181The 182.Fn msleep 183function appeared in 184.Fx 5.0 , 185and the 186.Fn msleep_spin 187function appeared in 188.Fx 7.0 . 189.Pp 190The 191.Fn sleep 192function used to be the traditional form. 193It did not let you specify a timeout or a 194.Fa wmesg , 195hence it was discontinued. 196.Sh AUTHORS 197.An -nosplit 198This manual page was written by 199.An J\(:org Wunsch Aq joerg@FreeBSD.org . 200