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teliva/src/task.lua

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----------------------------------------------------------------------------
-- Go style Channels for Lua
-- https://github.com/majek/lua-channels
--
-- This code is derived from libtask library by Russ Cox, mainly from
-- channel.c. Semantically channels as implemented here are quite
-- similar to channels from the Go language.
--
-- Usage (we're using unbuffered channel here):
--
-- local task = require('task')
--
-- local function counter(channel)
-- local i = 1
-- while true do
-- channel:send(i)
-- i = i + 1
-- end
-- end
--
-- local function main()
-- local channel = task.Channel:new()
-- task.spawn(counter, channel)
-- assert(channel:recv() == 1)
-- assert(channel:recv() == 2)
-- assert(channel:recv() == 3)
-- end
--
-- task.spawn(main)
-- task.scheduler()
--
--
-- This module exposes:
--
-- task.spawn(fun, [...]) - run fun as a coroutine with given
-- parameters. You should use this instead of
-- coroutine.create()
--
-- task.scheduler() - can be run only from the main thread, executes
-- all the stuff, resumes the coroutines that are
-- blocked on channels that became available. You
-- can only do non-blocking sends / receives from
-- the main thread.
--
-- task.Channel:new([buffer size]) - create a new channel with given size
--
-- task.chanalt(alts, can_block) - run alt / select / multiplex over
-- the alts structure. For example:
--
-- task.chanalt({{c = channel_1, op = task.RECV},
-- {c = channel_2, op = task.SEND, p = "hello"}}, true)
--
-- This will block current coroutine until it's possible to receive
-- from channel_1 or send to channel_2. chanalt returns a number of
-- statement from alts that succeeded (1 or 2 here) and a received
-- value if executed statement was RECV.
--
-- Finally, if two alt statements can be fulfilled at the same time,
-- we use math.random() to decide which one should go first. So it
-- makes sense to initialize seed with something random. If you don't
-- have access to an entropy source you can do:
-- math.randomseed(os.time())
-- but beware, the results of random() will predictable to a attacker.
----------------------------------------------------------------------------
local _M = {}
-- Constants
local RECV = 0x1
local SEND = 0x2
local NOP = 0x3
-- Global objects for scheduler
local tasks_runnable = {} -- list of coroutines ready to be resumed
----------------------------------------------------------------------------
--- Helpers
local function random_choice(arr)
if #arr > 1 then
return arr[math.random(#arr)]
else
return arr[1]
end
end
-- Specialised Set data structure (with random element selection)
local Set = {
new = function(self)
local o = {a = {}, l = {}}; setmetatable(o, self); self.__index = self
return o
end,
add = function(self, v)
local a, l = self.a, self.l
if a[v] == nil then
table.insert(l, v)
a[v] = #l
return true
end
end,
remove = function(self, v)
local a, l = self.a, self.l
local i = a[v]
if i > 0 then
local t = l[#l]
a[t], l[i] = i, t
a[i], l[#l] = nil, nil
return true
end
end,
random = function(self, v)
return random_choice(self.l)
end,
len = function(self)
return #self.l
end,
}
-- Circular Buffer data structure
local CircularBuffer = {
new = function(self, size)
local o = {b = {}, slots = size + 1, size = size, l = 0, r = 0}
setmetatable(o, self); self.__index = self
return o
end,
len = function(self)
return (self.r - self.l) % self.slots
end,
pop = function(self)
assert(self.l ~= self.r)
local v = self.b[self.l]
self.l = (self.l + 1) % self.slots
return v
end,
push = function(self, v)
self.b[self.r] = v
self.r = (self.r + 1) % self.slots
assert(self.l ~= self.r)
end,
}
----------------------------------------------------------------------------
-- Scheduling
--
-- Tasks ready to be run are placed on a stack and it's possible to
-- starve a coroutine.
local function scheduler()
local self_coro, is_main = coroutine.running()
-- We actually don't care if scheduler is run from the main
-- coroutine. But we do need to make sure that user doesn't do
-- blocking operation from it, as it can't yield.
-- Be compatible with 5.1 and 5.2
assert(not(self_coro ~= nil and is_main ~= true),
"Scheduler must be run from the main coroutine.")
local i = 0
while #tasks_runnable > 0 do
local co = table.remove(tasks_runnable)
local okay, emsg = coroutine.resume(co)
if not okay then
error(emsg)
end
i = i + 1
end
return i
end
local function task_ready(co)
table.insert(tasks_runnable, co)
end
local function spawn(fun, ...)
local args = {...}
local f = function()
fun(unpack(args))
end
local co = coroutine.create(f)
task_ready(co)
end
----------------------------------------------------------------------------
-- Channels - chanalt and helpers
-- Given two Alts from a single channel exchange data between
-- them. It's implied that one is RECV and another is SEND. Channel
-- may be buffered.
local function altcopy(a, b)
local r, s, c = a, b, a.c
if r.op == SEND then
r, s = s, r
end
assert(s == nil or s.op == SEND)
assert(r == nil or r.op == RECV)
-- Channel is empty or unbuffered, copy directly
if s ~= nil and r and c._buf:len() == 0 then
r.alt_array.value = s.p
return
end
-- Otherwise it's always okay to receive and then send.
if r ~= nil then
r.alt_array.value = c._buf:pop()
end
if s ~= nil then
c._buf:push(s.p)
end
end
-- Given enqueued alt_array from a chanalt statement remove all alts
-- from the associated channels.
local function altalldequeue(alt_array)
for i = 1, #alt_array do
local a = alt_array[i]
if a.op == RECV or a.op == SEND then
a.c:_get_alts(a.op):remove(a)
end
end
end
-- Can this Alt be execed without blocking?
local function altcanexec(a)
local c, op = a.c, a.op
if c._buf.size == 0 then
if op ~= NOP then
return c:_get_other_alts(op):len() > 0
end
else
if op == SEND then
return c._buf:len() < c._buf.size
elseif op == RECV then
return c._buf:len() > 0
end
end
end
-- Alt can be execed so find a counterpart Alt and exec it!
local function altexec(a)
local c, op = a.c, a.op
local other_alts = c:_get_other_alts(op)
local other_a = other_alts:random()
-- other_a may be nil
altcopy(a, other_a)
if other_a ~= nil then
-- Disengage from channels used by the other Alt and make it ready.
altalldequeue(other_a.alt_array)
other_a.alt_array.resolved = other_a.alt_index
task_ready(other_a.alt_array.task)
end
end
function ischannel(x)
return type(x) == "table" and x.__index == _M.Channel
end
-- The main entry point. Call it `alt` or `select` or just a
-- multiplexing statement. This is user facing function so make sure
-- the parameters passed are sane.
local function chanalt(alt_array, canblock)
assert(#alt_array)
local list_of_canexec_i = {}
for i = 1, #alt_array do
local a = alt_array[i]
a.alt_array = alt_array
a.alt_index = i
assert(type(a.op) == "number" and
(a.op == RECV or a.op == SEND or a.op == NOP),
"op field must be RECV, SEND or NOP in alt")
assert(ischannel(a.c),
"pass valid channel to a c field of alt")
if altcanexec(a) == true then
table.insert(list_of_canexec_i, i)
end
end
if #list_of_canexec_i > 0 then
local i = random_choice(list_of_canexec_i)
altexec(alt_array[i])
return i, alt_array.value
end
if canblock ~= true then
return nil
end
local self_coro, is_main = coroutine.running()
alt_array.task = self_coro
assert(self_coro ~= nil and is_main ~= true,
"Unable to block from the main thread, run scheduler.")
for i = 1, #alt_array do
local a = alt_array[i]
if a.op ~= NOP then
a.c:_get_alts(a.op):add(a)
end
end
-- Make sure we're not woken by someone who is not the scheduler.
alt_array.resolved = nil
coroutine.yield()
assert(alt_array.resolved > 0)
local r = alt_array.resolved
return r, alt_array.value
end
----------------------------------------------------------------------------
-- Channel object
local Channel = {
new = function(self, buf_size)
local o = {}; setmetatable(o, self); self.__index = self
o._buf = CircularBuffer:new(buf_size or 0)
o._recv_alts, o._send_alts = Set:new(), Set:new()
return o
end,
send = function(self, msg)
assert(chanalt({{c = self, op = SEND, p = msg}}, true) == 1)
return true
end,
recv = function(self)
local alts = {{c = self, op = RECV}}
local s, msg = chanalt(alts, true)
assert(s == 1)
return msg
end,
nbsend = function(self, msg)
local s = chanalt({{c = self, op = SEND, p = msg}}, false)
return s == 1
end,
nbrecv = function(self)
local s, msg = chanalt({{c = self, op = RECV}}, false)
return s == 1, msg
end,
_get_alts = function(self, op)
return (op == RECV) and self._recv_alts or self._send_alts
end,
_get_other_alts = function(self, op)
return (op == SEND) and self._recv_alts or self._send_alts
end,
__tostring = function(self)
return string.format("<Channel size=%i/%i send_alt=%i recv_alt=%i>",
self._buf:len(), self._buf.size, self._send_alts:len(),
self._recv_alts:len())
end,
__call = function(self)
local function f(s, v)
return true, self:recv()
end
return f, nil, nil
end,
}
----------------------------------------------------------------------------
-- Public interface
_M.scheduler = scheduler
_M.spawn = spawn
_M.Channel = Channel
_M.chanalt = chanalt
_M.RECV = RECV
_M.SEND = SEND
_M.NOP = NOP
----------------------------------------------------------------------------
----------------------------------------------------------------------------
-- Tests
local task = _M
function test_counter()
local done
local function counter(c)
local i = 1
while true do
c:send(i)
i = i + 1
end
end
local function main()
local c = task.Channel:new()
task.spawn(counter, c)
assert(c:recv() == 1)
assert(c:recv() == 2)
assert(c:recv() == 3)
assert(c:recv() == 4)
assert(c:recv() == 5)
done = true
end
task.spawn(main)
task.scheduler()
assert(done)
end
function test_nonblocking_channel()
local done
local function main()
local b = task.Channel:new()
assert(b:nbsend(1) == false)
assert(b:nbrecv() == false)
local c = task.Channel:new(1)
assert(c:nbrecv() == false)
assert(c:nbsend(1) == true)
assert(c:nbsend(1) == false)
local r, v = c:nbrecv()
assert(r == true)
assert(v == 1)
assert(c:nbrecv() == false)
done = true
end
task.spawn(main)
task.scheduler()
assert(done)
end
function test_concurrent_send_and_recv()
local l = {}
local function a(c, name)
-- Blocking send and recv from the same process
local alt = {{c = c, op = task.SEND, p = 1},
{c = c, op = task.RECV}}
local i, v = task.chanalt(alt, true)
local k = string.format('%s %s', name, i == 1 and "send" or "recv")
l[k] = (l[k] or 0) + 1
end
for i = 0, 1000 do
-- On Mac OS X in lua 5.1 initializing seed with a
-- predictable value makes no sense. For all seeds from 1 to
-- 1000 the result of math.random(1,3) is _exactly_ the same!
-- So beware, when seeding!
-- math.randomseed(i)
local c = task.Channel:new()
task.spawn(a, c, "a")
task.spawn(a, c, "b")
task.scheduler()
end
-- Make sure we have randomness, that is: events occur in both
-- orders in 1000 runs
assert(l['a recv'] > 0)
assert(l['a send'] > 0)
assert(l['b recv'] > 0)
assert(l['b send'] > 0)
end
function test_channels_from_a_coroutine()
local done
local c = task.Channel:new()
local function a()
for i = 1, 100 do
c:send(i)
end
end
local function b()
assert(c:recv() == 1)
assert(c:recv() == 2)
assert(c:recv() == 3)
assert(c:recv() == 4)
assert(c:recv() == 5)
done = true
end
local a_co = coroutine.create(a)
local b_co = coroutine.create(b)
coroutine.resume(a_co)
coroutine.resume(b_co)
task.scheduler()
assert(done)
end
function test_fibonacci()
local done
local function fib(c)
local x, y = 0, 1
while true do
c:send(x)
x, y = y, x + y
end
end
local function main(c)
assert(c:recv() == 0)
assert(c:recv() == 1)
assert(c:recv() == 1)
assert(c:recv() == 2)
assert(c:recv() == 3)
assert(c:recv() == 5)
assert(c:recv() == 8)
assert(c:recv() == 13)
assert(c:recv() == 21)
assert(c:recv() == 34)
done = true
end
local c = task.Channel:new()
task.spawn(fib, c)
task.spawn(main, c)
task.scheduler()
assert(done)
end
function test_non_blocking_chanalt()
local done
local function main()
local c = task.Channel:new()
local alts = {{c = c, op = task.RECV},
{c = c, op = task.NOP},
{c = c, op = task.SEND, p = 1}}
assert(task.chanalt(alts, false) == nil)
local c = task.Channel:new(1)
local alts = {{c = c, op = task.RECV},
{c = c, op = task.NOP},
{c = c, op = task.SEND, p = 1}}
assert(task.chanalt(alts, false) == 3)
assert(task.chanalt(alts, false) == 1)
local alts = {{c = c, op = task.NOP}}
assert(task.chanalt(alts, false) == nil)
done = true
end
task.spawn(main)
task.scheduler()
assert(done)
end
-- Apparently it's not really a Sieve of Eratosthenes:
-- http://www.cs.hmc.edu/~oneill/papers/Sieve-JFP.pdf
function test_eratosthenes_sieve()
local done
local function counter(c)
local i = 2
while true do
c:send(i)
i = i + 1
end
end
local function filter(p, recv_ch, send_ch)
while true do
local i = recv_ch:recv()
if i % p ~= 0 then
send_ch:send(i)
end
end
end
local function sieve(primes_ch)
local c = task.Channel:new()
task.spawn(counter, c)
while true do
local p, newc = c:recv(), task.Channel:new()
primes_ch:send(p)
task.spawn(filter, p, c, newc)
c = newc
end
end
local function main()
local primes = task.Channel:new()
task.spawn(sieve, primes)
assert(primes:recv() == 2)
assert(primes:recv() == 3)
assert(primes:recv() == 5)
assert(primes:recv() == 7)
assert(primes:recv() == 11)
assert(primes:recv() == 13)
done = true
end
task.spawn(main)
task.scheduler()
assert(done)
end
function test_channel_as_iterator()
local done
local function counter(c)
local i = 2
while true do
c:send(i)
i = i + 1
end
end
local function main()
local numbers = task.Channel:new()
task.spawn(counter, numbers)
for _, j in numbers() do
if j == 100 then
break
end
done = true
end
end
if _VERSION == "Lua 5.1" then
-- sorry, this test doesn't work in 5.1
print('S')
done = true
else
task.spawn(main)
task.scheduler()
end
assert(done)
end
return _M
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