30211738911

Committed 26 Jul 2026 05:02PM UTC coverage: 85.343% (+0.1%) from 85.229%

Build # 30211738911

Build Type

push

github

Committed by

Tieske

Commit Message

fix(semaphore): take() must reject requests below 1 or NaN

A negative `requested` on the fast path (`count = count - requested`)
turned a take into a give, inflating `count` past `max` with no check
at all (eg. take(-100) on a max=5 semaphore left count at 100). A NaN
request would queue forever, since `count >= NaN` is always false and
can never be satisfied, deadlocking that entry and everyone behind it
in the FIFO queue. Reject both instead.

Coverage Stats

2 of 2 new or added lines in 1 file covered. (100.0%)

9 existing lines in 5 files now uncovered.

1444 of 1692 relevant lines covered (85.34%)

55080.61 hits per line

Source File
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100.0

/src/copas/future.lua

local copas = require("copas")
local semaphore = require("copas.semaphore")

local pcall = pcall
if _VERSION == "Lua 5.1" and not jit then  -- obsolete: only for Lua 5.1 compatibility
  pcall = require("coxpcall").pcall
end


-- nil-safe versions for pack/unpack
local _unpack = unpack or table.unpack
local unpack = function(t, i, j) return _unpack(t, i or 1, j or t.n or #t) end
local pack = function(...) return { n = select("#", ...), ...} end



-- Module table

local M = {}

M.SUCCESS = true
M.PENDING = false
M.ERROR   = "error"

setmetatable(M, {
  __index = function(_, k)
    error("unknown field 'future." .. tostring(k) .. "'", 2)
  end,
})



-- Future class

local future = {}
future.__index = future

-- calling on the future executes the `get` method
future.__call = function(self, ...) return self:get(...) end


local function new_future()
  local self = setmetatable({
    results = nil, -- results will be stored here in a 'packed' table (pcall-style: true/false prefix)
    sema = semaphore.new(math.huge, 0, math.huge),
    coro = nil -- the coroutine that will execute the task
  }, future)

  return self
end


-- Waits for the task to complete.
-- Returns like pcall: true + results on success, false + errmsg on error.
function future:get()
  if not self.results then
    self.sema:take(1, math.huge) -- wait until the result is ready
  end
  return unpack(self.results)
end


-- Non-blocking check on the future status.
-- Returns:
--   M.PENDING (false)             -- task not yet complete
--   M.SUCCESS (true), results...  -- task completed successfully
--   M.ERROR ("error"), errmsg     -- task failed with an error
function future:try()
  if not self.results then
    return M.PENDING
  end
  if self.results[1] then
    return M.SUCCESS, unpack(self.results, 2)
  else
    return M.ERROR, self.results[2]
  end
end


-- Cancels the task if it has not yet completed.
-- Returns true if cancelled, false if already done.
function future:cancel()
  if self.results then
    return false  -- already done (or already cancelled)
  end
  self.results = pack(false, "cancelled")
  self.sema:release_all()
  copas.removethread(self.coro)
  return true
end



-- Module implementation

-- Mimics copas.addnamedthread but returns a future instead of the coroutine.
function M.addnamedthread(name, func, ...)
  local f = new_future()

  f.coro = copas.addnamedthread(name, function(...)
    local results
    local ok, err = pcall(function(...) results = pack(true, func(...)) end, ...)
    if not ok then
      results = pack(false, err)
    end
    if not f.results then  -- don't overwrite a cancel
      f.results = results
      f.sema:release_all()
    end
  end, ...)

  return f
end


-- Mimica copas.addthread but returns a future instead of the coroutine.
function M.addthread(func, ...)
  return M.addnamedthread(nil, func, ...)
end


return M

1	local copas = require("copas")	6✔
2	local semaphore = require("copas.semaphore")	6✔
3
4	local pcall = pcall	6✔
5	if _VERSION == "Lua 5.1" and not jit then -- obsolete: only for Lua 5.1 compatibility	6✔
UNCOV 6	pcall = require("coxpcall").pcall	1✔
7	end
8
9
10	-- nil-safe versions for pack/unpack
11	local _unpack = unpack or table.unpack	6✔
12	local unpack = function(t, i, j) return _unpack(t, i or 1, j or t.n or #t) end	108✔
13	local pack = function(...) return { n = select("#", ...), ...} end	78✔
14
15
16
17	-- Module table
18
19	local M = {}	6✔
20
21	M.SUCCESS = true	6✔
22	M.PENDING = false	6✔
23	M.ERROR = "error"	6✔
24
25	setmetatable(M, {	12✔
26	__index = function(_, k)
27	error("unknown field 'future." .. tostring(k) .. "'", 2)	6✔
28	end,
29	})
30
31
32
33	-- Future class
34
35	local future = {}	6✔
36	future.__index = future	6✔
37
38	-- calling on the future executes the `get` method
39	future.__call = function(self, ...) return self:get(...) end	12✔
40
41
42	local function new_future()
43	local self = setmetatable({	144✔
44	results = nil, -- results will be stored here in a 'packed' table (pcall-style: true/false prefix)	60✔
45	sema = semaphore.new(math.huge, 0, math.huge),	84✔
46	coro = nil -- the coroutine that will execute the task	60✔
47	}, future)	72✔
48
49	return self	72✔
50	end
51
52
53	-- Waits for the task to complete.
54	-- Returns like pcall: true + results on success, false + errmsg on error.
55	function future:get()	6✔
56	if not self.results then	96✔
57	self.sema:take(1, math.huge) -- wait until the result is ready	84✔
58	end
59	return unpack(self.results)	96✔
60	end
61
62
63	-- Non-blocking check on the future status.
64	-- Returns:
65	-- M.PENDING (false) -- task not yet complete
66	-- M.SUCCESS (true), results... -- task completed successfully
67	-- M.ERROR ("error"), errmsg -- task failed with an error
68	function future:try()	6✔
69	if not self.results then	24✔
70	return M.PENDING	6✔
71	end
72	if self.results[1] then	18✔
73	return M.SUCCESS, unpack(self.results, 2)	7✔
74	else
75	return M.ERROR, self.results[2]	12✔
76	end
77	end
78
79
80	-- Cancels the task if it has not yet completed.
81	-- Returns true if cancelled, false if already done.
82	function future:cancel()	6✔
83	if self.results then	18✔
84	return false -- already done (or already cancelled)	6✔
85	end
86	self.results = pack(false, "cancelled")	14✔
87	self.sema:release_all()	12✔
88	copas.removethread(self.coro)	12✔
89	return true	12✔
90	end
91
92
93
94	-- Module implementation
95
96	-- Mimics copas.addnamedthread but returns a future instead of the coroutine.
97	function M.addnamedthread(name, func, ...)	6✔
98	local f = new_future()	72✔
99
100	f.coro = copas.addnamedthread(name, function(...)	144✔
101	local results
102	local ok, err = pcall(function(...) results = pack(true, func(...)) end, ...)	136✔
103	if not ok then	60✔
104	results = pack(false, err)	14✔
105	end
106	if not f.results then -- don't overwrite a cancel	60✔
107	f.results = results	60✔
108	f.sema:release_all()	60✔
109	end
110	end, ...)	204✔
111
112	return f	72✔
113	end
114
115
116	-- Mimica copas.addthread but returns a future instead of the coroutine.
117	function M.addthread(func, ...)	6✔
118	return M.addnamedthread(nil, func, ...)	66✔
119	end
120
121
122	return M	6✔

lunarmodules / copas / 30211738911

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