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93 thread.closeable_channel

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% vim: ft=mercury ts=4 sw=4 et
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% Copyright (C) 2020 The Mercury team.
% This file is distributed under the terms specified in COPYING.LIB.
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%
% File: thread.closeable_channel.m.
% Main author: wangp.
% Stability: low.
%
% Unbounded closeable channels.
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:- module thread.closeable_channel.
:- interface.

:- import_module bool.
:- import_module io.

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:- type closeable_channel(T).

    % Initialise a channel.
    %
:- pred init(closeable_channel(T)::out, io::di, io::uo) is det.

    % Put an item at the end of the channel.
    % Returns `yes' if successful, or `no' if the channel is closed.
    %
:- pred put(closeable_channel(T)::in, T::in, bool::out, io::di, io::uo)
    is det.

    % Close a channel. Once a channel is closed, no more items can be added
    % to it. Closing a channel that is already closed has no effect.
    %
:- pred close(closeable_channel(T)::in, io::di, io::uo) is det.

:- type take_result(T)
    --->    ok(T)
    ;       closed.

    % Take an item from the start of the channel, blocking until an item is
    % available or until the channel is closed. Returns `ok(Item)' if `Item'
    % was taken, or `closed' if the channel is closed.
    %
:- pred take(closeable_channel(T)::in, take_result(T)::out, io::di, io::uo)
    is det.

:- type try_take_result(T)
    --->    ok(T)
    ;       closed
    ;       would_block.

    % Take an item from the start of the channel, but do not block.
    % Returns `ok(Item)' if `Item' was taken from the channel,
    % `closed' if no item was taken because the channel is closed, or
    % `would_block' if no item could be taken from the channel without
    % blocking. `would_block' may be returned even if the channel is not
    % empty.
    %
:- pred try_take(closeable_channel(T)::in, try_take_result(T)::out,
    io::di, io::uo) is det.

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