Enables a barrier, waits until a specified number of arrivers arrive, and then wakes immediately.
mp
barrier-block-and-wait barrier count &key wait-if-used-p errorp timeout unblock => result
barrier⇩ |
A barrier. |
count⇩ |
A positive integer. |
wait-if-used-p⇩ |
A generalized boolean. |
errorp⇩ |
A boolean. |
timeout⇩ |
A non-negative real or nil . |
unblock⇩ |
A boolean. |
result⇩ |
An integer, a symbol or a mp:process object. |
The function barrier-block-and-wait
enables the barrier barrier with t
, that is it makes any number of arrivers wait, and then waits until count arrivers arrive.
wait-if-used-p controls whether to wait if another process is already inside barrier-block-and-wait
. The default value of wait-if-used-p is nil
.
barrier is a barrier made by make-barrier.
errorp controls whether to signal an error if another process is already inside barrier-block-and-wait
and wait-if-used-p is nil
. The default value of errorp is nil
.
timeout, if non-nil, specifies the time in seconds to wait before timing out. The default value of timeout is nil
.
unblock specifies whether processes that already wait on barrier should be unblocked first. The default value of unblock is nil
.
barrier-block-and-wait
is "using" barrier, and only one process can do this the same time. barrier-block-and-wait
first tries to mark barrier as used by the current process, which will fail if another process is inside barrier-block-and-wait
with the same barrier. In this case it does one of three options:
Once barrier-block-and-wait
has successfully marked barrier as used, it changes its count to t
as if by calling (barrier-change-count barrier t)
, which will cause other barrier-wait calls to wait. If unblock is non-nil, it first unblocks all processes that wait on the barrier, so the effect is the same as (barrier-enable barrier t)
.
It then waits until the arriver count of barrier is greater than or equal to count, or, if timeout is supplied, timeout seconds passed. It then returns the number of arrivers.
result can be one of three types:
barrier was in use, and wait-if-used-p is non-nil, so barrier-wait was called. result is the result of barrier-wait. | |
mp:process |
barrier-block-and-wait
returns. barrier is still set with t
, that is calls to barrier-wait on barrier will wait. Normally the current process will go on to do some operations that require the other processes to wait, and then release them by calling barrier-disable or barrier-enable.barrier-block-and-wait
with wait-if-used-p non-nil), barrier-block-and-wait
will return after count processes called barrier-wait and are waiting. That is the intended purpose of barrier-block-and-wait
. If other processes call functions that manipulate the arriver count or the count of barrier (barrier-disable, barrier-enable, barrier-unblock, barrier-change-count), then barrier-block-and-wait
will "get confused", in the sense that while its behavior is still well-defined, it is not intuitive.barrier-block-and-wait
is useful for controlling a fixed set of processes by another "master" process. The processes in the set need to call barrier-wait at appropriate points. When the "master" process wants to stop them for a while, it calls barrier-block-and-wait
. When it wants to restart them, it calls barrier-disable.barrier-block-and-wait
with wait-if-used-p non-nil (and count the number of processes in the group minus one). If two of the processes happen to call it at the same time, one will get the barrier, and the other process will have to wait.barrier-block-and-wait
can be approximated by using barrier-change-count followed by normal process-wait that checks the arrivers count in the wait function. barrier-block-and-wait
has two advantages:
(a) It checks against more than one process trying to do it at the same time.
(b) barrier-block-and-wait
will wake up immediately when the arriver count reaches the right number. process-wait will wake up only when the scheduler checks the wait function and wakes it up.
barrier
barrier-wait
make-barrier
barrier-enable
barrier-disable
19.7.2 Synchronization barriers
LispWorks® User Guide and Reference Manual - 01 Dec 2021 19:30:51