*nix Documentation Project
·  Home
 +   man pages
·  Linux HOWTOs
·  FreeBSD Tips
·  *niX Forums

  man pages->OpenBSD man pages -> tsleep (9)              



NAME    [Toc]    [Back]

     sleep, tsleep, wakeup - process context sleep and wakeup

SYNOPSIS    [Toc]    [Back]

     #include <sys/types.h>
     #include <sys/proc.h>

     tsleep(void *ident, int priority,  const  char  *wmesg,  int

     sleep(void *ident, int priority);

     wakeup(void *ident);

DESCRIPTION    [Toc]    [Back]

     These   functions  implement  voluntary  context  switching.
tsleep() and
     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)
which are
               temporarily unavailable.

           +o    The  current  process wants access to data structures which are
               locked by other processes.

     The function wakeup() is used to notify  sleeping  processes
of possible
     changes  to  the  condition that caused them to go to sleep.
Typically, an
     awakened process will -- after it  has  acquired  a  context
again -- retry
     the action that blocked its operation to see if the ``blocking'' condition
 has cleared.

     The bpendsleep label can be used as a break-point to debug a
process coming
 back from tsleep().

     The tsleep() function takes the following arguments:

     ident     An identifier of the ``wait channel'' representing
the resource
               for which the current process needs to wait.  This
typically is
               the  virtual address of some kernel data structure
related to
               the resource for which the process is  contending.
The same
               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
is awakened
               and  put on the queue of runnable processes.  This
mechanism is
               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
timo/hz seconds.
   If  this  amount  of  time  elapses and no
wakeup(ident) has
               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
always reevaluate
 the conditions that blocked them, since a  call  to
wakeup() merely
  signals  a  possible  change to the blocking conditions.
For example,
     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.
All others
     will have to go back to sleep and wait for the next opportunity.

RETURN VALUES    [Toc]    [Back]

     tsleep()  returns 0 if it returns as a result of a wakeup().
If a
     tsleep() returns as a result of a signal, the  return  value
     the  signal  has the SA_RESTART property (see sigaction(2)),
and EINTR otherwise.
  If tsleep() returns as a result of a  timeout,  the
return value

CODE REFERENCES    [Toc]    [Back]

     These    functions    are    implemented    in    the   file

SEE ALSO    [Toc]    [Back]

     hz(9), mi_switch(9), timeout(9)

OpenBSD     3.6                           June      23,      1996
[ Back ]
 Similar pages
Name OS Title
wakeup NetBSD process context sleep and and wakeup
ltsleep NetBSD process context sleep and and wakeup
tsleep NetBSD process context sleep and and wakeup
sleep NetBSD process context sleep and and wakeup
sleep Tru64 General: Puts a calling process to sleep
ctxsw NetBSD switch to another process context
ctxsw OpenBSD switch to another process context
cpu_switch OpenBSD switch to another process context
mi_switch OpenBSD switch to another process context
mi_switch NetBSD switch to another process context
Copyright © 2004-2005 DeniX Solutions SRL
newsletter delivery service