sleep, tsleep, wakeup - process context sleep and wakeup
tsleep(void *ident, int priority, const char *wmesg, int
sleep(void *ident, int priority);
These functions implement voluntary context switching.
sleep() are used throughout the kernel whenever processing
in the current
context can not continue for any of the following reasons:
+o The current process needs to await the results of
a pending I/O
+o The current process needs resources (e.g., memory)
+o The current process wants access to data structures which are
locked by other processes.
The function wakeup() is used to notify sleeping processes
changes to the condition that caused them to go to sleep.
awakened process will -- after it has acquired a context
again -- retry
the action that blocked its operation to see if the ``blocking'' condition
The bpendsleep label can be used as a break-point to debug a
back from tsleep().
The tsleep() function takes the following arguments:
ident An identifier of the ``wait channel'' representing
for which the current process needs to wait. This
the virtual address of some kernel data structure
the resource for which the process is contending.
identifier must be used in a call to wakeup() to
get the process
going again. ident should not be NULL.
priority The process priority to be used when the process
and put on the queue of runnable processes. This
used to optimize ``throughput'' of processes executing in kernel
mode. If the flag PCATCH is OR'ed into
priority the process
checks for posted signals before and after
wmesg A pointer to a character string indicating the
reason a process
is sleeping. The kernel does not use the string,
but makes it
available (through the process structure field
p_wmesg) for user
level utilities such as ps(1).
timo If non-zero, the process will sleep for at most
If this amount of time elapses and no
occurred, and no signal (if PCATCH was set) was
tsleep() will return EWOULDBLOCK.
The sleep() function puts the process in an uninterruptible
sleep. It is
functionally equivalent to:
tsleep(ident, priority & PRIMASK, 0, 0)
The wakeup() function will mark all processes which are currently sleeping
on the identifier ident as runnable. Eventually, each
of the processes
will resume execution in the kernel context, causing
a return from
[t]sleep(). Note that processes returning from sleep should
the conditions that blocked them, since a call to
signals a possible change to the blocking conditions.
when two or more processes are waiting for an exclusive
lock, only one of
them will succeed in acquiring the lock when it is released.
will have to go back to sleep and wait for the next opportunity.
tsleep() returns 0 if it returns as a result of a wakeup().
tsleep() returns as a result of a signal, the return value
is ERESTART if
the signal has the SA_RESTART property (see sigaction(2)),
and EINTR otherwise.
If tsleep() returns as a result of a timeout, the
These functions are implemented in the file
hz(9), mi_switch(9), timeout(9)
OpenBSD 3.6 June 23, 1996
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