Provided by: freebsd-manpages_6.2-1_all bug

NAME

      sleep, msleep, tsleep, wakeup - wait for events

SYNOPSIS

      #include <sys/param.h>
      #include <sys/systm.h>
      #include <sys/proc.h>
 
      int
      tsleep(void *ident, int priority, const char *wmesg, int timo);
 
      int
      msleep(void *ident, struct mtx *mtx, int priority, const char *wmesg,
              int timo);
 
      void
      wakeup(void *ident);
 
      void
      wakeup_one(void *ident);

DESCRIPTION

      The functions tsleep() and wakeup() handle event-based process blocking.
      If a process must wait for an external event, it is put on sleep by
      tsleep().  The parameter ident is an arbitrary address that uniquely
      identifies the event on which the process is being asleep.  All processes
      sleeping on a single ident are woken up later by wakeup(), often called
      from inside an interrupt routine, to indicate that the resource the pro‐
      cess was blocking on is available now.
 
      The parameter wmesg is a string describing the sleep condition for tools
      like ps(1).  Due to the limited space of those programs to display arbi‐
      trary strings, this message should not be longer than 6 characters.
 
      The wakeup_one() function is used to make the first process in the queue
      that is sleeping on the parameter ident runnable.  This can prevent the
      system from becoming saturated when a large number of processes are
      sleeping on the same address, but only one of them can actually do any
      useful work when made runnable.
 
      The tsleep() function is the general sleep call.  Suspends the current
      process until a wakeup is performed on the specified identifier.  The
      process will then be made runnable with the specified priority.  Sleeps
      at most timo / hz seconds (0 means no timeout).  If the Giant lock is not
      held and mtx is NULL, then timo must be non-zero.  If priority includes
      the PCATCH flag, signals are checked before and after sleeping, else sig‐
      nals are not checked.  Returns 0 if awakened, EWOULDBLOCK if the timeout
      expires.  If PCATCH is set and a signal needs to be delivered, ERESTART
      is returned if the current system call should be restarted if possible,
      and EINTR is returned if the system call should be interrupted by the
      signal (return EINTR).
 
      The msleep() function is a variation on tsleep.  The parameter mtx is a
      mutex which will be released before sleeping and reacquired before
      msleep() returns.  If priority includes the PDROP flag, the mtx parameter
      will not be reacquired before returning.  The mutex is used to ensure
      that a condition can be checked atomically, and that the current process
      can be suspended without missing a change to the condition, or an associ‐
      ated wakeup.
      See above.
      ps(1), malloc(9), mi_switch(9)

HISTORY

      The sleep/wakeup process synchronization mechanism is very old.  It
      appeared in a very early version of UNIX.
 
      The tsleep() function appeared in 4.4BSD.
 
      The sleep() function used to be the traditional form.  It did not let you
      specify a timeout or a wmesg, hence it was discontinued.

AUTHORS

      This manual page was written by Jörg Wunsch 〈joerg@FreeBSD.org〉.