latch_wait, latch_trywait --
acquire a latch
cc . . . -lsuds
int latch_wait(latch_t *latch, int type, int timeout);
int latch_trywait(latch_t *latch, int type, int timeout);
acquire a latch; block if latch is already held
acquire a latch; return an error if latch is already held
The latch_wait function locks the latch referenced by
latch by performing the latch lock operation on that
latch. If the latch is currently locked by another process, then the
calling process does not return from the call to
latch_wait until it locks the latch, the call is
interrupted by a signal or the timeout expires. The mechanism by
which the process blocks is controlled by the latch type
as set by the process which is currently holding the latch. The
timeout is also set by the process holding the latch.
The latch_trywait function locks the latch referenced by
latch only if the latch is currently not locked. Otherwise
it does not lock the latch.
Upon successful return, the state of the latch is locked and owned
by the calling process. It remains locked until the
function is executed and returns successfully.
A latch's blocking mechanism is not fixed. It is modified by calls
to latch_wait and latch_trywait. There are
several available blocking mechanisms:
timeout controls the amount of time latch_wait
blocks for before returning with an error condition modifying how it
blocks. timeout is in microseconds and has a maximum value
of 268435455; a value of 0 represents an indefinite wait. For
LT_SPIN and LT_SPIN_SLEEP locks, all processes
blocking on a particular latch increment a global value representing
the total spin time on that latch since it was last acquired. The
timeout occurs when the global value reaches timeout.
Blocked processes spin waiting for the latch. This is efficient only
if the process holding the latch does so for a period of time less
than about 17000 CPU cycles. If the latch is likely to be
held for longer than this period, or system calls will be made by
the process whilst holding the latch, it is strongly recommended
that LT_SLEEP be used.
Blocked processes sleep (see
This is efficient if the latch is likely to be held for a period of
time greater than about 17000 CPU cycles or if system
calls will be made whilst holding the latch.
The process spins until the timeout occurs. When the timeout occurs
the process blocks using
with an indefinite timeout.
The latch_wait and latch_trywait functions
return zero if the calling process successfully performed the latch
lock operation on the latch designated by latch. If the
call was unsuccessful, the state of the latch remains unchanged and
the function returns -1 and sets errno to indicate the
Errors returned are as for
together with the following additional error:
A timeout interrupted this function.
If a process exits or execs whilst holding a latch the system will
post the latch and produce the following warning message on the
WARNING: latches held at exec/close time
latch_wait and latch_trywait are not part of any
currently supported standard; they are an extension of
AT&T System V provided by The Santa Cruz Operation, Inc.
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003