This library provides queue (FIFO) data structure and its operations.
You can create a simple queue, which is not thread-safe, or an MT queue, a thread-safe queue. Basic queue operations work on both type of queues. When a mtqueue is passed to the procedures listed in this section, each operation is done in atomic way, unless otherwise noted.
There are also a set of procedures for mtqueues that can be used for thread synchronisation; for example, you can let the consumer thread block if an mtqueue is empty, and/or the producer thread block if the number of items in the mtqueue reaches a specified limit. Using these procedures allows the program to use an mtqueue as a channel.
The simple queue API is a super set of SLIB's queue implementation.
NOTE: (util deque) is used as underlying library.
A class of simple queue.
A class of mtqueue. Inherits <queue>.
Creates and return an empty simple queue.
Creates and return an empty mtqueue.
The keyword argument max-length specifies the maximum entry count of the queue. Negative number indicates unlimited number of entry. If the given number is zero then the queue cannot hold any item.
Returns #t if obj is a queue (either a simple queue or an mtqueue).
Returns #t if obj is an mtqueue.
Returns #t if queue is an empty queue.
Returns the number of the items in the queue.
Returns the maximum number of items mtqueue can hold. #f indicates unlimited.
Returns the number of elements mtqueue can accept at this moment
before it hits its maximum length. If the queue has unlimited capacity then
the procedure returns +inf.0.
Returns a copy of queue.
Adds obj to the end of queue. You may give more than one object, and each of them are enqueued in order.
If queue is an mtqueue, all the objects are enqueued atomically; no
other objects from other threads can be inserted between the objects given
to a single enqueue! call. Besides, if the value of the result of
mtqueue-max-length is positive, and adding objs makes the
number of element in queue exceeds it, an error is raised and
queue won't be modified. (If the maximum length is zero, this procedure
always fail. Use enqueue/wait! below.)
Adds obj to in front of queue. You may give more than one object, and each of them are pushed in order.
Like enqueue!, when queue is an mtqueue, all objects are added
atomically, and the value of max length is checked. See enqueue! above
for more detail.
Like enqueue! and queue-push!, respectively, except that
these don't modify queue if it already contains objs (elements are
compared by two-argument procedure eq-proc).
When queue is an mtqueue, all objects are added atomically, and the max
length is checked. See enqueue! above for the detail.
Take one object from the front of queue and return it. Both
function work the same, but queue-pop! may be used to emphasize it
works with queue-push!.
If queue is empty, fallback is returned if give, otherwise an error is raised.
If queue is mtqueue and its max length is zero, then the queue is
always empty. Use dequeue/wait! to use such a queue as a
synchronisation device.
Returns the whole content of queue by a list, with emptying
queue. If queue is empty, returns an empty list. See also
queue->list below.
Peek the head or the tail of queue and return the object, respectively.
If queue is empty, fallback is returned if give, otherwise an error is raised.
Returns a new queue which content is the elements in list, in the given order.
By default the created queue is a simple queue, but you can create mtqueue
or instance of other subclass <queue> by giving the class to the
optional class arguments. The optional initargs arguments are
passed to the constructor of class.
Returns a list whose content is the items in queue in order.
Unlike dequeue-all!, the content of queue remains intact.
The returning list is a copy of the content. So modifying the list won't
affect queue.
Returns the first item in queue that satisfies a predicate pred.
Apply pred on each item in queue until it evaluates true, and returns that true value. If no item satisfies pred, #f is returned.
Apply pred on each item in queue. If pred returns #f, stops iteration and returns #f immediately. Otherwise, returns the result of pred on the last item of queue. If the queue is empty, #t is returned.
Removes all items in queue that satisfies pred. Returns #t if any item is removed. Otherwise #f.
These synchronising variants work on an mtqueue and make the caller
thread block when the mtqueue has reached its maximum length (for
enqueue/wait! and queue-push/wait!), or the mtqueue is empty
(for dequeue/wait! and queue-pop/wait!). The blocked caller
thread is unblocked either the blocking condition is resolved, or the
timeout condition is met.
The optional timeout argument specifies the timeout condition. If it is #f, those procedure wait indefinitely. If it is a real number, they wait at least the given number of seconds.
In case the call is blocked then timed out, the value of timeout-val is returned, which default value is #t.
When enqueue/wait! and queue-push/wait! succeeds without hitting
timeout, they return #t.