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.

1 files changed, 61 insertions, 0 deletions

diff --git a/util/smqueue.lua b/util/smqueue.lua
new file mode 100644
index 00000000..d24c35ae
--- /dev/null
+++ b/util/smqueue.lua
@@ -0,0 +1,61 @@
+local queue = require("util.queue");
+
+local lib = { smqueue = {} }
+
+local smqueue = lib.smqueue;
+
+function smqueue:push(v)
+	self._head = self._head + 1;
+
+	assert(self._queue:push(v));
+end
+
+function smqueue:ack(h)
+	if h < self._tail then
+		return nil, "tail"
+	elseif h > self._head then
+		return nil, "head"
+	end
+
+	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() return self._head - self._tail end
+
+function smqueue:count_acked() return self._tail end
+
+function smqueue:resumable() return self._queue:count() >= (self._head - self._tail) end
+
+function smqueue:resume() return self._queue:items() end
+
+function smqueue:consume() return self._queue:consume() end
+
+local compat_mt = {}
+
+function compat_mt:__index(i)
+	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() return self._queue:count_unacked() end
+
+function smqueue:table() return setmetatable({ _queue = self }, compat_mt) end
+
+local function freeze(q) return { head = q._head; tail = q._tail } end
+
+local queue_mt = { __name = "smqueue"; __index = smqueue; __len = smqueue.count_unacked; __freeze = freeze }
+
+function lib.new(size)
+	assert(size > 0);
+	return setmetatable({ _head = 0; _tail = 0; _queue = queue.new(size, true) }, queue_mt)
+end
+
+return lib