SLEEP(10.2) SLEEP(10.2)
NAME
sleep, wakeup, tsleep, return0 - process synchronisation
SYNOPSIS
void sleep(Rendez *r, int (*f)(void*), void *arg)
void wakeup(Rendez *r)
void tsleep(Rendez *r, int (*f)(void*), void *arg, int ms)
int return0(void *arg)
DESCRIPTION
A process running in the kernel can use these functions to synchronise
with an interrupt handler or another kernel process. In particular,
they are used by device drivers to wait for an event to be signalled on
receipt of an interrupt. (In practice, they are most often used indi‐
rectly, through qio(10.2) for instance.)
The caller of sleep and a caller of wakeup share a Rendez structure, to
provide a rendezvous point between them to synchronise on an event.
Sleep uses a condition function f that returns true if the event has
occurred.
Sleep evaluates f(arg). If true, the event has happened and sleep
returns immediately. Otherwise, sleep blocks on the event variable r,
awaiting wakeup.
Wakeup is called by either a process or an interrupt handler to wake
any process sleeping at r, signifying that the corresponding condition
is true (the event has occurred). It has no effect if there is no
sleeping process.
Tsleep is similar to sleep, except that if the condition f(arg) is
false and the caller does sleep, and nothing else wakes it within ms
millliseconds, the system will wake it. Tsleep's caller must check its
environment to decide whether timeout or the event occurred. The tim‐
ing provided by tsleep is imprecise, but adequate in practice for the
normal use of protecting against lost interrupts and otherwise unre‐
sponsive devices or software.
Return0 ignores its arguments and returns zero. It is commonly used as
the predicate f in a call to tsleep to obtain a time delay, using a
Rendez variable sleep in the Proc structure, for example:
tsleep(&up->sleep, return0, nil, 10);
Both sleep and tsleep can be interrupted by swiproc (see kproc(10.2)),
causing a non-local goto through a call to error(10.2).
DIAGNOSTICS
There can be at most one process waiting on a Rendez, and if two pro‐
cesses collide, the system will panic(10.2) (``double sleep''). Access
to a Rendez must therefore be serialised by some other mechanism, usu‐
ally qlock(10.2).
SOURCE
/os/port/proc.c
/emu/port/proc.c
SEE ALSO
lock(10.2), qlock(10.2), delay(10.2)
``Process Sleep and Wakeup on a Shared-memory Multiprocessor'', in Plan
9 Programmer's Manual: Volume 2 .
SLEEP(10.2)
