2 .\" Copyright (c) 1996 Joerg Wunsch
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40 .Fd #include <sys/param.h>
41 .Fd #include <sys/systm.h>
42 .Fd #include <sys/proc.h>
44 .Fn tsleep "void *ident" "int priority" "const char *wmesg" "int timo"
46 .Fn msleep "void *ident" "struct mtx *mtx" "int priority" "const char *wmesg" "int timo"
48 .Fn asleep "void *ident" "int priority" "const char *wmesg" "int timo"
50 .Fn await "int priority" "int timo"
52 .Fn wakeup "void *ident"
54 .Fn wakeup_one "void *ident"
60 handle event-based process blocking. If a process must wait for an
61 external event, it is put on sleep by
65 is an arbitrary address that uniquely identifies the event on which
66 the process is being asleep. All processes sleeping on a single
70 often called from inside an interrupt routine, to indicate that the
71 resource the process was blocking on is available now.
75 is a string describing the sleep condition for tools like
77 Due to the limited space of those programs to display arbitrary strings,
78 this message should not be longer than 6 characters.
82 function is used to make the first process in the queue that is
83 sleeping on the parameter
85 runnable. This can prevent the system from becoming saturated
86 when a large number of processes are sleeping on the same address,
87 but only one of them can actually do any useful work when made
91 is the general sleep call. Suspends the current process until a wakeup is
92 performed on the specified identifier. The process will then be made
93 runnable with the specified
97 \&/ hz seconds (0 means no timeout). If
101 flag, signals are checked before and after sleeping, else signals are
102 not checked. Returns 0 if awakened,
104 if the timeout expires. If
106 is set and a signal needs to be delivered,
108 is returned if the current system call should be restarted if
111 is returned if the system call should be interrupted by the signal
116 is a variation on tsleep. The parameter
118 is a mutex, which will be exited before sleeping, and entered before
126 parameter will not be entered before returning. The mutex is
127 used to ensure that a condition can be checked atomicly, and
128 that the current process can be suspended without missing a
129 change to the condition, or an associated wakeup.
132 implements the new asynchronous sleep function. It takes the same arguments
135 and places the process on the appropriate wait queue, but
137 leaves the process runnable and returns immediately. The caller is then
138 expected to, at some point in the future, call
140 to actually wait for the previously queued wait condition.
143 is called several times, only the most recent call is effective.
145 may be called with an
148 to remove any previously queued condition.
151 implements the new asynchronous wait function. When
153 is called on an identifier it associates the process with that
154 identifier but does not block.
156 will actually block the process until
158 is called on that identifier any time after the
168 call is effectively a NOP.
171 is called multiple times without an intervening
175 is effectively a NOP but will also call
179 function allows you to override the priority and timeout values to be used.
180 If the value -1 is specified for an argument, the value is taken from the
183 call. If -1 is passed for the priority you must be prepared to catch signal
184 conditions if the prior call to
186 specified it in its priority. If -1 is passed for the timeout you must be
187 prepared to catch a timeout condition if the prior call to
189 specified a timeout. When you use -1, it is usually a good idea to not make
190 assumptions as to the arguments used by the prior
198 functions are mainly used by the kernel to shift the burden of blocking
199 away from extremely low level routines and to push it onto their callers.
200 This in turn allows more complex interlocking code to
202 of a temporary resource failure
203 (such as lack of memory) in order to release major locks prior to actually
204 blocking, and to then retry the operation on wakeup. This key feature is
205 expected to be heavily used in SMP situations in order to allow code to make
206 better use of spinlocks. A spinlock, by its very nature, cannot be used
207 around code that might block. It is hoped that these capabilities will
208 make it easier to migrate the SMP master locks deeper into the kernel.
210 These routines may also be used to avoid nasty spl*() calls to get around
211 race conditions with simple conditional test/wait interlocks. You simply
214 prior to your test, then conditionally
216 only if the test fails. It is usually a good idea to cancel an
218 if you wind up never calling the related
220 but it is not required. If you do not want to waste cpu calling
222 unnecessarily, you can surround the whole thing with a second test. The
223 race condition is still handled by the inside
233 The sleep/wakeup process synchronization mechanism is very old. It
234 appeared in a very early version of Unix.
240 .Nm Asleep Ns / Ns Nm await
243 and is designed to shift the burden of blocking
244 away from extremely low level routines and push it up to their callers.
247 used to be the traditional form. It doesn't let you specify a timeout or a
249 hence it has been discontinued.
252 This man page was written by
257 were designed and written by