Module `Squeue`

Thread-safe queue module, using locks.

type 'a t

val sexp_of_t : ('a -> Ppx_sexp_conv_lib.Sexp.t) -> 'a t -> Ppx_sexp_conv_lib.Sexp.t

val create : int -> 'a t: create maxsize returns a synchronized queue bounded to have no more than maxsize elements.

val push : 'a t -> 'a -> unit: Blocks until there's room on the queue, then pushes.

val push_uncond : 'a t -> 'a -> unit: Does not block, may grow the queue past maxsize.

val push_or_drop : 'a t -> 'a -> bool: Pushes an event on the queue if the queue is less than maxsize, otherwise drops it. Returns true if the push was successful

val length : 'a t -> int: Returns the number of elements in the queue.

val pop : 'a t -> 'a: Pops an element off the queue, blocking until something is available

val lpop : 'a t -> 'a * int: Returns the element popped and the length of the queue this element was popped.

val transfer_queue_in : 'a t -> 'a Core_kernel.Linked_queue.t -> unit: Transfers all the elements from an ordinary queue into the squeue. Blocks until there's room on the queue, then pushes. May grow queue past maxsize.

val transfer_queue_in_uncond : 'a t -> 'a Core_kernel.Linked_queue.t -> unit
val transfer_queue : 'a t -> 'a Core_kernel.Linked_queue.t -> unit: Transfers all elements from the squeue to an ordinary queue. The elements remain in order. Waits until at least one element can be transferred.

val transfer_queue_nowait : 'a t -> 'a Core_kernel.Linked_queue.t -> unit: Transfers all elements from the squeue to an ordinary queue. The elements remain in order. Does not wait for elements to arrive.

val clear : 'a t -> unit: Clears the queue

val wait_not_empty : 'a t -> unit

wait_not_empty sq waits for something to be available. This is useful if you want to wait, but not take something out. This function is not useful in most cases, but in some complex cases it is essential. For example, if you need to take another lock before you remove something from the queue for processing, you might want to try to take that other lock, and if it fails do something else.

This function is not dangerous, there is just one thing you have to remember if you use it: Just because this function returns doesn't mean that pop will succeed; someone might have gotten there first, so you have to use transfer_queue_nowait if you don't want to block.