From 93a9ed262065d9966643ad5ae50b58142a1c6823 Mon Sep 17 00:00:00 2001
From: Kim Alvefur <zash@zash.se>
Date: Tue, 14 Dec 2021 19:58:53 +0100
Subject: util.smqueue: Abstract queue with acknowledgements and overflow

Meant to be used in mod_smacks for XEP-0198

Meant to have a larger virtual size than actual number of items stored,
on the theory that in most cases, the excess will be acked before needed
for a resumption event.
---
 teal-src/util/smqueue.tl | 107 +++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 107 insertions(+)
 create mode 100644 teal-src/util/smqueue.tl

(limited to 'teal-src')

diff --git a/teal-src/util/smqueue.tl b/teal-src/util/smqueue.tl
new file mode 100644
index 00000000..0bbceb8e
--- /dev/null
+++ b/teal-src/util/smqueue.tl
@@ -0,0 +1,107 @@
+local queue = require "util.queue";
+
+local record lib
+	-- T would typically be util.stanza
+	record smqueue<T>
+		_queue : queue.queue<T>
+		_head : integer
+		_tail : integer
+
+		enum ack_errors
+			"tail"
+			"head"
+			"pop"
+		end
+		push : function (smqueue, T)
+		ack : function (smqueue, integer) : { T }, ack_errors
+		resumable : function (smqueue) : boolean
+		type consume_iter = function (smqueue<T>) : T
+		consume : function (smqueue<T>) : consume_iter
+
+		table : function (smqueue<T>) : { T }
+	end
+	new : function <T>(integer) : smqueue<T>
+end
+
+local type smqueue = lib.smqueue;
+
+function smqueue:push(v)
+	self._head = self._head + 1;
+	-- Wraps instead of errors
+	assert(self._queue:push(v));
+end
+
+function smqueue:ack(h : integer) : { any }, smqueue.ack_errors
+	if h < self._tail then
+		return nil, "tail";
+	elseif h > self._head then
+		return nil, "head";
+	end
+	-- TODO optimize? cache table fields
+	local acked = {};
+	self._tail = h;
+	local expect = self._head - self._tail;
+	while expect < self._queue:count() do
+		local v = self._queue:pop();
+		if not v then return nil, "pop"; end
+		table.insert(acked, v);
+	end
+	return acked;
+end
+
+function smqueue:count_unacked() : integer
+	return self._head - self._tail;
+end
+
+function smqueue:count_acked() : integer
+	return self._tail;
+end
+
+function smqueue:resumable() : boolean
+	return self._queue:count() >= (self._head - self._tail);
+end
+
+function smqueue:resume() : queue.queue.iterator, any, integer
+	return self._queue:items();
+end
+
+function smqueue:consume() : queue.queue.consume_iter
+	return self._queue:consume()
+end
+
+-- Compatibility wrapper, meant to look like a plain ol' array
+local record compat_mt
+	_queue : smqueue<any>
+end
+
+function compat_mt:__index(i : integer) : any
+	if i < self._queue._tail then return nil end
+	return self._queue._queue._items[(i + self._queue._tail) % self._queue._queue.size];
+end
+
+function compat_mt:__len() : integer
+	return self._queue:count_unacked()
+end
+
+function smqueue:table() : { any }
+	return setmetatable({ _queue = self }, compat_mt);
+end
+
+local function freeze(q : smqueue<any>) : { string:integer }
+	return { head = q._head, tail = q._tail }
+end
+
+local queue_mt = {
+	--
+	__name = "smqueue";
+	__index = smqueue;
+	__len = smqueue.count_unacked;
+	__freeze = freeze;
+}
+
+function lib.new<T>(size : integer) : queue.queue<T>
+	assert(size>0);
+	return setmetatable({ _head = 0; _tail = 0; _queue = queue.new(size, true) }, queue_mt);
+end
+
+return lib;
-- 
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