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% vim: ft=mercury ts=4 sw=4 et
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% Copyright (C) 2000-2001, 2006-2007 The University of Melbourne.
% Copyright (C) 2014-2015, 2018, 2020-2022 The Mercury team.
% This file is distributed under the terms specified in COPYING.LIB.
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%
% File: thread.channel.m.
% Main author: petdr.
% Stability: low.
%
% A mvar can only contain a single value, a channel on the other hand provides
% unbounded buffering.
%
% For example a program could consist of 2 worker threads and one logging
% thread. The worker threads can place messages into the channel, and they
% will be buffered for processing by the logging thread.
%
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:- module thread.channel.
:- interface.

:- import_module io.
:- import_module maybe.

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:- type channel(T).

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

    % Put an item at the end of the channel.
    %
:- pred put(channel(T)::in, T::in, io::di, io::uo) is det.

    % Take an item from the start of the channel, block if there is
    % nothing in the channel.
    %
:- pred take(channel(T)::in, T::out, io::di, io::uo) is det.

    % Take an item from the start of the channel.
    % Returns immediately with no if the channel was empty.
    %
:- pred try_take(channel(T)::in, maybe(T)::out, io::di, io::uo) is det.

    % Duplicate a channel. The new channel sees all (and only) the
    % data written to the channel after the `duplicate'/4 call.
    %
:- pred duplicate(channel(T)::in, channel(T)::out, io::di, io::uo)
    is det.

    % Place an item back at the start of the channel.
    %
    % WARNING: a call to channel.untake will deadlock if a call to
    % channel.take is blocked on the same channel.
    %
:- pred untake(channel(T)::in, T::in, io::di, io::uo) is det.
:- pragma obsolete(pred(untake/4)).

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