From ea436776c735608d8993776e660c4ca210eab510 Mon Sep 17 00:00:00 2001
From: cloudfreexiao <996442717qqcom@gmail.com>
Date: Fri, 20 Aug 2021 21:42:58 +0800
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=B3chore(=E5=BA=93):=E5=A2=9E=E5=8A=A0?=
 =?UTF-8?q?=20=E4=BA=8B=E4=BB=B6=20=E5=BA=93?=
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Content-Type: text/plain; charset=UTF-8
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---
 docs/README.md                         |   4 +
 framework/lualib/3rd/notify/dqueue.lua | 109 +++++++
 framework/lualib/3rd/notify/event.lua  | 431 +++++++++++++++++++++++++
 framework/lualib/3rd/notify/signal.lua | 352 ++++++++++++++++++++
 4 files changed, 896 insertions(+)
 create mode 100755 framework/lualib/3rd/notify/dqueue.lua
 create mode 100755 framework/lualib/3rd/notify/event.lua
 create mode 100755 framework/lualib/3rd/notify/signal.lua

diff --git a/docs/README.md b/docs/README.md
index 0973851..b46373d 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -17,6 +17,10 @@ https://github.com/hellogcc/100-gdb-tips
 Modern Unix Command
 https://github.com/ibraheemdev/modern-unix
 
+A tool for writing better scripts
+https://github.com/google/zx
+
+
 https://github.com/cloudwu/skynet/issues/288
 
 
diff --git a/framework/lualib/3rd/notify/dqueue.lua b/framework/lualib/3rd/notify/dqueue.lua
new file mode 100755
index 0000000..b797458
--- /dev/null
+++ b/framework/lualib/3rd/notify/dqueue.lua
@@ -0,0 +1,109 @@
+local setmetatable = setmetatable
+
+local DoubleQueue = {}
+
+-- Class attributes and methods goes on this table --
+local DoubleQueueObject = {}
+
+-- Metamethods goes on this table --
+local DoubleQueueObject_mt = {
+    __index = DoubleQueueObject,
+}
+
+-- Module exported functions --
+
+---
+-- Creates a new double queue.
+function DoubleQueue.new()
+    local object = setmetatable({}, DoubleQueueObject_mt)
+
+    -- create all the instance state data.
+    object.data = {}
+    object.data_position = {}
+    object.first = 1
+    object.last = 0
+    return object
+end
+
+-- Private methods --
+local function refresh_first(self)
+    while (self.first <= self.last) do
+        if (self.data[self.first]) then
+            return true
+        end
+        self.first = self.first + 1
+    end
+end
+
+-- Public methods --
+
+---
+-- Check if the queue is empty
+-- @return true if it is empty, false otherwise.
+function DoubleQueueObject:is_empty()
+    return self.first > self.last
+end
+
+---
+-- Pushes data on the front of the queue.
+-- @param data The data thas is being pushed.
+function DoubleQueueObject:push_front(data)
+    if (self.data_position[data]) then
+        return
+    end
+    self.first = self.first - 1
+    self.data[self.first] = data
+    self.data_position[data] = self.first
+end
+
+---
+-- Pushes data on the back of the queue.
+-- @param data The data thas is being pushed.
+function DoubleQueueObject:push_back(data)
+    if (self.data_position[data]) then
+        return
+    end
+    self.last = self.last + 1
+    self.data[self.last] = data
+    self.data_position[data] = self.last
+end
+
+---
+-- Get the queue iterator.
+-- Each call to the iterator function returns the next element.
+-- Example:
+--
+--    for data in queue:get_iterator() do
+--        print("mydata: "..tostring(data))
+--    end
+--
+-- @return An iterator function.
+function DoubleQueueObject:get_iterator()
+    local first = self.first
+    local function iterator()
+        while (first <= self.last) do
+            local data = self.data[first]
+            first = first + 1
+            if (data) then
+                return data
+            end
+        end
+    end
+    return iterator
+end
+
+---
+-- Removes the first ocurrence of data from the queue.
+-- If the data cant be found on the queue, nothing happens.
+-- @param data The data that is going the be removed.
+function DoubleQueueObject:remove(data)
+    if (not self.data_position[data]) then
+        return
+    end
+    self.data[self.data_position[data]] = nil
+    self.data_position[data] = nil
+    refresh_first(self)
+end
+
+return DoubleQueue
+
diff --git a/framework/lualib/3rd/notify/event.lua b/framework/lualib/3rd/notify/event.lua
new file mode 100755
index 0000000..ba9cea7
--- /dev/null
+++ b/framework/lualib/3rd/notify/event.lua
@@ -0,0 +1,431 @@
+--- https://github.com/katcipis/luanotify
+
+
+-- This module aims to build a generic hierarchic event system.
+-- The hierarchic model uses string event names to define what event are you working with.
+--
+-- For example:
+--
+-- *  "event"              -> Just a normal event.
+-- *  "event:subevent"     -> Using the subevent feature.
+--
+-- The ":" is what defines that you are using hierarchic events,
+-- every ":" you put is a new hierarchic level.
+--
+-- When emiting "event:subevent", everyone connected at "event" and "event:subevent"
+-- is going to be notified. When emitting "event", only the ones connected at "event" are
+-- going to be notified.
+--
+-- Using this hierarchical structure it is easy to be notified only when a specific event happens
+-- or when a whole bunch of events inside a category happens. All events can be expressed on a tree,
+-- where a node is a event, and you can connect,add a pre emit, add a post emit,
+-- disconnect, block, unblock, emit, on any node of the tree.
+--
+-- @class module
+-- @name notify.event
+local setmetatable = setmetatable
+local string = string
+local unpack = unpack
+
+local Queue = require "notify.dqueue"
+local separator = ":"
+
+-- Module exported functions
+local Event = {}
+
+-- Class attributes and methods goes on this table --
+local EventObject = {}
+
+-- Metamethods goes on this table --
+local EventObject_mt = {
+    __index = EventObject,
+}
+
+-- Private methods definition --
+local function new_node()
+    return {
+        handlers = Queue.new(),
+        pre_emits = Queue.new(),
+        post_emits = Queue.new(),
+        blocked_handlers = {},
+        subevents = {},
+    }
+end
+
+local function get_nodes_names(event_name)
+    local nodes_names = {}
+    for n in string.gmatch(event_name, "[^" .. separator .. "]+") do
+        nodes_names[#nodes_names + 1] = n
+    end
+    return nodes_names
+end
+
+local function get_node(self, event_name)
+    local events_names = get_nodes_names(event_name)
+    local current_node = self.events[events_names[1]] or new_node()
+
+    self.events[events_names[1]] = current_node
+    for i = 2, #events_names do
+        local sub_node = current_node.subevents[events_names[i]] or new_node()
+        current_node.subevents[events_names[i]] = sub_node
+        current_node = sub_node
+    end
+    return current_node
+end
+
+local function unused_event(self, event_name)
+    local events_names = get_nodes_names(event_name)
+    local current_node = self.events[events_names[1]]
+
+    if not current_node then
+        return true
+    end
+
+    for i = 2, #events_names do
+        local sub_node = current_node.subevents[events_names[i]]
+        if not sub_node then
+            return true
+        end
+        current_node = sub_node
+    end
+
+    return false
+end
+
+local function event_iterator(self, event_name)
+    local events_names = get_nodes_names(event_name)
+    local i = 2
+    local current_node = self.events[events_names[1]]
+
+    local function iterator()
+        if not current_node then
+            return
+        end
+        local ret = current_node
+
+        if events_names[i] then
+            current_node = current_node.subevents[events_names[i]]
+            i = i + 1
+        else
+            current_node = nil
+        end
+
+        return ret
+    end
+
+    return iterator
+end
+
+local function call_pre_emits(self, event_name)
+    local nodes = Queue.new()
+    local reversed_nodes = Queue.new()
+
+    for node in event_iterator(self, event_name) do
+        for pre_emit in node.pre_emits:get_iterator() do
+            pre_emit(event_name)
+        end
+        nodes:push_back(node)
+        reversed_nodes:push_front(node)
+    end
+
+    return nodes, reversed_nodes
+end
+
+local function call_post_emits(event_name, reversed_nodes)
+    for node in reversed_nodes:get_iterator() do
+        for post_emit in node.post_emits:get_iterator() do
+            post_emit(event_name)
+        end
+    end
+end
+
+local function call_handlers(self, params)
+    for node in params.nodes:get_iterator() do
+        for handler in node.handlers:get_iterator() do
+            if (self.stopped) then
+                return
+            end
+            if (node.blocked_handlers[handler] == 0) then
+                if (params.accumulator) then
+                    params.accumulator(handler(params.event_name, unpack(params.args)))
+                else
+                    handler(params.event_name, unpack(params.args))
+                end
+            end
+        end
+    end
+end
+
+-- Module exported functions
+
+---
+-- Creates a new Event object.
+-- @return The new Event object.
+function Event.new()
+    local object = setmetatable({}, EventObject_mt)
+
+    -- create all the instance state data.
+    object.stopped = false
+    object.events = {}
+    return object
+end
+
+-- Class definition and methods --
+
+---
+-- Connects a handler function on this event.
+-- If any subevent is emitted, this handler will be called too.
+-- @param event_name       - The event name.
+-- @param handler_function - The function that will be called when the event_name is emitted.
+function EventObject:connect(event_name, handler_function)
+    local node = get_node(self, event_name)
+    node.handlers:push_back(handler_function)
+
+    if not node.blocked_handlers[handler_function] then
+        node.blocked_handlers[handler_function] = 0
+    end
+end
+
+---
+-- Disconnects a handler function on this event.
+-- @param event_name       - The event name.
+-- @param handler_function - The function that will be disconnected.
+function EventObject:disconnect(event_name, handler_function)
+    if unused_event(self, event_name) then
+        return
+    end
+
+    local node = get_node(self, event_name)
+    node.handlers:remove(handler_function)
+    node.blocked_handlers[handler_function] = nil
+end
+
+---
+-- Does not execute the given handler function when the give event is emitted until it is unblocked. 
+-- It can be called several times for the same handler function.
+--
+-- Example:
+--
+--    local Event = require "notify.event"
+--    local event = Event.new()
+
+--    local function handler1(arg)
+--        print(arg)
+--    end
+--
+--    event:connect("mouse", handler1)
+--    event:emit("mouse", "example") -- example gets printed.
+--
+--    event:block("mouse", handler1);
+--    event:emit("mouse", "example") -- nothing gets printed.
+--
+--
+-- @param event_name - The event name.
+-- @param handler_function - The handler function that will be blocked.
+function EventObject:block(event_name, handler_function)
+    if unused_event(self, event_name) then
+        return
+    end
+
+    local node = get_node(self, event_name)
+    local block = node.blocked_handlers[handler_function]
+    if block then
+        node.blocked_handlers[handler_function] = block + 1
+    end
+end
+
+---
+-- Unblocks the handler function from the given event.
+-- The calls to unblock must match the calls to block.
+--
+-- Example:
+--
+--    local Event = require "notify.event"
+--    local event = Event.new()
+--
+--    local function handler1(arg)
+--        print(arg)
+--    end
+--
+--    event:connect("mouse", handler1)
+--    event:emit("mouse", "example") -- example gets printed.
+--
+--    event:block("mouse", handler1);
+--    event:emit("mouse", "example") -- nothing gets printed.
+--
+--    event:block("mouse", handler1);
+--    event:emit("mouse", "example") -- nothing gets printed.
+--
+--    event:unblock("mouse", handler1);
+--    event:emit("mouse", "example") -- nothing gets printed.
+--    event:unblock("mouse", handler1);
+--    event:emit("mouse", "example") -- example gets printed.
+--
+--
+-- @param event_name - The event name.
+-- @param handler_function - The handler function that will be unblocked.
+function EventObject:unblock(event_name, handler_function)
+    if unused_event(self, event_name) then
+        return
+    end
+
+    local node = get_node(self, event_name)
+    if node.blocked_handlers[handler_function] and node.blocked_handlers[handler_function] > 0 then
+
+        node.blocked_handlers[handler_function] = node.blocked_handlers[handler_function] - 1
+    end
+end
+
+---
+-- Emits an event and all handler functions connected to it will be called.
+-- Emiting the event "event1::event2::event3" will call the handlers connected
+-- on the following events, on this order:
+--  * event1
+--  * event1:event2
+--  * event1:event2:event3
+--
+-- @param event_name - The event name.
+-- @param ...  - A optional list of parameters, they will be repassed to the handler functions connected to this event.
+function EventObject:emit(event_name, ...)
+    self.stopped = false
+    local nodes, reversed_nodes = call_pre_emits(self, event_name)
+    call_handlers(self, {
+        event_name = event_name,
+        nodes = nodes,
+        args = {...},
+    })
+    call_post_emits(event_name, reversed_nodes)
+end
+
+---
+-- Typical emission discards handlers return values completely.
+-- This is most often what you need: just inform the world about something.
+-- However, sometimes you need a way to get feedback.
+-- For instance, you may want to ask: “is this value acceptable ?”
+-- This is what accumulators are for. Accumulators are specified to events at emission time.
+-- They can combine, alter or discard handlers return values, post-process them or even stop emission. 
+-- Since a handler can return multiple values, accumulators can receive multiple args too.
+-- Following Lua flexible style we give the user the freedom to do whatever he wants with accumulators. 
+-- If you are using the hierarchic event system the behaviour of handlers calling is similar to the emit function.
+-- @param event_name  - The event name. 
+-- @param accumulator - Function that will receive handlers results or a table to accumulate
+--                      all the handlers returned values.
+-- @param ...         - A optional list of parameters, they will be repassed to the handler
+--                      functions connected to this signal.
+function EventObject:emit_with_accumulator(event_name, accumulator, ...)
+    self.stopped = false
+    local nodes, reversed_nodes = call_pre_emits(self, event_name)
+    call_handlers(self, {
+        event_name = event_name,
+        nodes = nodes,
+        accumulator = accumulator,
+        args = {...},
+    })
+    call_post_emits(event_name, reversed_nodes)
+end
+
+---
+-- Adds a pre_emit func, pre_emit functions can't be blocked, only added or removed.
+-- They can't have their return collected by accumulators, they will not receive any data
+-- passed on the emission and they are always called before ANY handler is called.
+-- This is useful when you want to perform some global task before handling an event,
+-- like opening a socket that the handlers might need to use or a opening a database.
+-- pre_emit functions can make sure everything is ok before handling an event, reducing
+-- the need to do this check_ups inside the handler functions itself (sometimes multiple times).
+-- They are called on a queue (FIFO) policy based on the order they added.
+-- When using hierarchy, pre_emission happen top-bottom. For example, with a mouse::button1 event,
+-- first the pre_emit functions on mouse will be called, then mouse::button1 post_emit functions will be called.
+-- @param event_name    - The event name.
+-- @param pre_emit_func - The pre_emit function.
+function EventObject:add_pre_emit(event_name, pre_emit_func)
+    get_node(self, event_name).pre_emits:push_back(pre_emit_func)
+end
+
+---
+-- Removes a pre-emit func from the given event.
+-- @param event_name - The event name.
+-- @param pre_emit_func - The pre_emit function.
+function EventObject:remove_pre_emit(event_name, pre_emit_func)
+    if unused_event(self, event_name) then
+        return
+    end
+    get_node(self, event_name).pre_emits:remove(pre_emit_func)
+end
+
+---
+-- Adds a post_emit function, post_emit functions can't be blocked, only added or removed, 
+-- they can't have their return collected by accumulators, they will not receive any data passed 
+-- on the emission and they are always called after ALL handlers where called. 
+-- This is useful when you want to perform some global task after handling an event, 
+-- like closing a socket or a database that the handlers might need to use or do some cleanup. 
+-- post_emit functions can make sure everything is released after handling an event, reducing the need 
+-- to do this check_ups inside some handler function, since some resources can be shared by multiple handlers. 
+-- They are called on a stack (LIFO) policy  based on the order they added. When using hierarchy, 
+-- post_emission happen bottom-top. For example, with a mouse::button1 event, first the post_emit 
+-- functions on mouse::button1 will be called, then mouse post_emit functions will be called.
+-- @param event_name - The event name. 
+-- @param post_emit_func - The post_emit function.
+function EventObject:add_post_emit(event_name, post_emit_func)
+    get_node(self, event_name).post_emits:push_front(post_emit_func)
+end
+
+---
+-- Removes a post-emit func from the given event.
+-- @param event_name - The event name.
+-- @param post_emit_func - The post_emit function.
+function EventObject:remove_post_emit(event_name, post_emit_func)
+    if unused_event(self, event_name) then
+        return
+    end
+    get_node(self, event_name).post_emits:remove(post_emit_func)
+end
+
+---
+-- Has effect only during a emission and will stop only this particular emission of the event.
+-- Usually called inside a pre-emit (when a condition fail) or on any handler.
+--
+-- Example:
+--
+--    local Event = require "notify.event"
+--    local event = Event.new()
+--
+--    function handler1()
+--        print("handler1")
+--        event.stop();
+--    end
+--
+--    function handler2()
+--        print("2")
+--    end
+--
+--    event:connect("mouse", handler1)
+--    event:connect("mouse::click", handler2)
+--
+--    event:emit("mouse::click") --handler2 never gets printed because handler1 always stops the emission
+--
+function EventObject:stop()
+    self.stopped = true
+end
+
+---
+-- Removes all pre/post-emits and handlers from the given event_name.
+-- If no name is given all pre/post-emits and handlers will be removed.
+-- @param event_name - The name of the event that will be cleared, or nil to clear all events.
+function EventObject:clear(event_name)
+    if (not event_name) then
+        self.events = {}
+        return
+    end
+end
+
+-- Public functions --
+local global_event = Event.new()
+
+---
+-- Always returns the same Event instance, this way is easy to share the same Event object across different modules.
+-- @return An EventObject instance.
+function Event.get_global_event()
+    return global_event
+end
+
+return Event
diff --git a/framework/lualib/3rd/notify/signal.lua b/framework/lualib/3rd/notify/signal.lua
new file mode 100755
index 0000000..41b5257
--- /dev/null
+++ b/framework/lualib/3rd/notify/signal.lua
@@ -0,0 +1,352 @@
+---
+-- Signal object implementation.
+-- @class module
+-- @name notify.signal
+local setmetatable = setmetatable
+local Queue = require "notify.dqueue"
+
+local Signal = {}
+
+-- Class attributes and methods goes on this table --
+local SignalObject = {}
+
+-- Metamethods goes on this table --
+local SignalObject_mt = {
+    __index = SignalObject,
+}
+
+-- Class definition and methods --
+
+---
+-- Disconnects a handler function from this signal, the function will no longer be called.
+-- Example:
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--
+--    function handler(arg)
+--        print(arg)
+--    end
+--
+--    s:connect(handler)
+--    s:emit("example") -- example gets printed
+--    s:disconnect(handler)
+--    s:emit("example") -- nothing gets printed
+--
+-- @param handler_function – The function that will be disconnected.
+function SignalObject:disconnect(handler_function)
+    self.handlers:remove(handler_function)
+    self.handlers_block[handler_function] = nil
+end
+
+---
+-- Connects a handler function on this signal, all handlers connected will be called 
+-- when the signal is emitted with a FIFO  behaviour (The first connected will be the first called).
+-- Example:
+--    local signal = require "notify.signal"
+--
+--    function handler1(arg)
+--        print(arg.."1")
+--    end
+--    function handler2(arg)
+--        print(arg.."2")
+--    end
+--
+--    local s = signal.new()
+--    s:connect(handler1)
+--    s:connect(handler2)
+--    s:emit("example") -- example1 gets printed before example2.
+--
+-- @param handler_function – The function that will be called when this signal is emitted.
+function SignalObject:connect(handler_function)
+    if (not self.handlers_block[handler_function]) then
+        self.handlers_block[handler_function] = 0
+        self.handlers:push_back(handler_function)
+    end
+end
+
+---
+-- Does not execute the given handler function when the signal is emitted until it is unblocked. 
+-- It can be called several times for the same handler function.
+-- Example:
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--
+--    function handler(arg)
+--        print(arg)
+--    end
+--
+--    s:connect(handler)
+--    s:emit("example") -- example gets printed
+--
+--    s:block(handler)
+--    s:emit("example") -- nothing gets printed
+--
+-- @param handler_function – The handler function that will be blocked.
+function SignalObject:block(handler_function)
+    if (self.handlers_block[handler_function]) then
+        self.handlers_block[handler_function] = self.handlers_block[handler_function] + 1
+    end
+end
+
+---
+-- Unblocks the given handler function, this handler function will be executed on 
+-- the order it was previously connected, and it will only be unblocked when 
+-- the calls to unblock are equal to the calls to block.
+-- Example:
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--    function handler(arg)
+--        print(arg)
+--    end
+--    s:connect(handler)
+--    s:emit("example")  -- example gets printed
+--    s:block(handler)
+--    s:emit("example") -- nothing gets printed
+--    s:block(handler)
+--    s:emit("example") -- nothing gets printed
+--    s:unblock(handler)
+--    s:emit("example") -- nothing gets printed
+--    s:unblock(handler)
+--    s:emit("example") -- example gets printed
+--
+-- @param handler_function – The handler function that will be unblocked.
+function SignalObject:unblock(handler_function)
+    if (self.handlers_block[handler_function]) then
+        if (self.handlers_block[handler_function] > 0) then
+            self.handlers_block[handler_function] = self.handlers_block[handler_function] - 1
+        end
+    end
+end
+
+---
+-- Emits a signal calling the handler functions connected to this signal passing the given args.
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--    function handler1(arg1, arg2)
+--        print(arg1)
+--        print(arg2)
+--    end
+--    function handler2(arg)
+--        print(arg)
+--    end
+
+--    s:connect(handler1)
+--    s:connect(handler2)
+--    s:emit("example") -- a nil will get printed because only one argument was passed
+--    s:emit("example1", "example2") -- No nil will get printed.
+--    s:emit() -- Only nils will get printed because no argument was passed.
+--
+-- @param … – A optional list of parameters, they will be repassed to the handler functions connected to this signal.
+function SignalObject:emit(...)
+    self.signal_stopped = false
+
+    for set_up in self.pre_emit_funcs:get_iterator() do
+        set_up()
+    end
+
+    for handler in self.handlers:get_iterator() do
+        if (self.signal_stopped) then
+            break
+        end
+        if (self.handlers_block[handler] == 0) then
+            handler(...)
+        end
+    end
+
+    for tear_down in self.post_emit_funcs:get_iterator() do
+        tear_down()
+    end
+end
+
+---
+-- Typical signal emission discards handler return values completely. 
+-- This is most often what you need: just inform the world about something. 
+-- However, sometimes you need a way to get feedback. For instance, 
+-- you may want to ask: “is this value acceptable ?”
+-- This is what accumulators are for. Accumulators are specified to signals at emission time. 
+-- They can combine, alter or discard handler return values, post-process them or even stop emission. 
+-- Since a handler can return multiple values, accumulators can receive multiple args too, following 
+-- Lua flexible style user has the freedom to do whatever he wants with accumulators.
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--
+--    function handler1(arg)
+--        return arg * 2
+--    end
+--
+--    function handler2(arg)
+--        return arg * 3
+--    end
+--
+--    local result = {}
+--    function accum(arg)
+--        result[#result+1] = arg
+--    end
+--
+--    s:connect(handler1)
+--    s:connect(handler2)
+--
+--    s:emit_with_accumulator(accum, 2)
+--
+--    for k,v in ipairs(result) do  -- print 4, 6
+--        print(v)
+--    end
+--
+-- @param accumulator – Function that will accumulate handlers results.
+-- @param … – A optional list of parameters, they will be repassed to the handler functions connected to this signal.
+function SignalObject:emit_with_accumulator(accumulator, ...)
+    self.signal_stopped = false;
+
+    for set_up in self.pre_emit_funcs:get_iterator() do
+        set_up()
+    end
+
+    for handler in self.handlers:get_iterator() do
+        if (self.signal_stopped) then
+            break
+        end
+        if (self.handlers_block[handler] == 0) then
+            accumulator(handler(...))
+        end
+    end
+
+    for tear_down in self.post_emit_funcs:get_iterator() do
+        tear_down()
+    end
+end
+
+---
+-- Adds a pre_emit func, pre_emit functions cant be blocked, only added or removed, 
+-- they cannot have their return collected by accumulators, will not receive any data passed 
+-- on the emission and they are always called before ANY handler is called. 
+-- This is useful when you want to perform some global task before handling an event, 
+-- like opening a socket that the handlers might need to use or a database, pre_emit functions 
+-- can make sure everything is ok before handling an event, reducing the need to do this check_ups 
+-- inside the handler function. They are called on a queue (FIFO) policy based on the order they added.
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--
+--    function handler1()
+--        print(1)
+--    end
+--
+--    function handler2()
+--        print(2)
+--    end
+--
+--    function pre_emit()
+--        print("0")
+--    end
+--
+--    s:connect(handler1)
+--    s:connect(handler2)
+--    s:emit() -- 1 and 2 printed.
+--    s:add_pre_emit(pre_emit)
+--    s:emit() -- 0,1 and 2 are printed.
+--
+-- @param pre_emit_func – The pre_emit function.
+function SignalObject:add_pre_emit(pre_emit_func)
+    self.pre_emit_funcs:push_back(pre_emit_func)
+end
+
+---
+-- Removes the pre_emit function
+-- @param pre_emit_func – The pre_emit function.
+function SignalObject:remove_pre_emit(pre_emit_func)
+    self.pre_emit_funcs:remove(pre_emit_func)
+end
+
+---
+-- Adds a post_emit function, post_emit functions cant be blocked, only added or removed, 
+-- they cannot have their return collected by accumulators, they will not receive any data 
+-- passed on the emission and they are always called after ALL handlers where called. 
+-- This is useful when you want to perform some global task after handling an event, 
+-- like closing a socket that the handlers might need to use or a database or do some cleanup. 
+-- post_emit functions can make sure everything is released after handling an event, 
+-- reducing the need to do this check_ups inside some handler function, since some resources 
+-- can be shared by multiple handlers. They are called on a stack (LIFO) policy based on the order they added.
+-- Example:
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--
+--    function handler1()
+--        print(1)
+--    end
+--
+--    function handler2()
+--        print(2)
+--    end
+--
+--    function post_emit()
+--        print("3")
+--    end
+--
+--    s:connect(handler1)
+--    s:connect(handler2)
+--    s:emit() -- 1 and 2 printed.
+--    s:add_post_emit(post_emit)
+--    s:emit() -- 1, 2 and 3 are printed.
+--
+-- @param post_emit_func – The post_emit function.
+function SignalObject:add_post_emit(post_emit_func)
+    self.post_emit_funcs:push_front(post_emit_func)
+end
+
+---
+-- Removes the post_emit function
+-- @param post_emit_func – The post_emit function.
+function SignalObject:remove_post_emit(post_emit_func)
+    self.post_emit_funcs:remove(post_emit_func)
+end
+
+---
+-- Stops the current emission, if there is any handler left to be called by the signal it wont be called.
+-- Example:
+--
+--    local signal = require "notify.signal"
+--    local s = signal.new()
+--
+--    local function handler1()
+--        print("hanlder1")
+--        signal:stop()
+--    end
+--
+--    local function handler2()
+--        print("hanlder2")
+--    end
+--
+--    s:connect(handler1)
+--    s:connect(handler2)
+--    s:emit() -- handler2 never gets printed because handler1 always stops the emission
+--
+function SignalObject:stop()
+    self.signal_stopped = true
+end
+
+-- Signal module exported functions --
+
+---
+-- Creates a new SignalObject.
+function Signal.new()
+    local object = {}
+    -- set the metatable of the new object as the SignalObject_mt table (inherits SignalObject).
+    setmetatable(object, SignalObject_mt)
+
+    -- create all the instance state data.
+    object.handlers_block = {}
+    object.handlers = Queue.new()
+    object.pre_emit_funcs = Queue.new()
+    object.post_emit_funcs = Queue.new()
+    object.signal_stopped = false
+    return object
+end
+
+return Signal
+