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|
local F = vim.F
local new_event = require('vim.async._event')
local pcall = pcall
do
local ok, coxpcall = pcall(require, 'coxpcall')
if ok and type(coxpcall) == 'table' and type(coxpcall.pcall) == 'function' then
pcall = coxpcall.pcall
end
end
local validate = vim.validate
--- A semaphore manages an internal permit counter. [Semaphore:acquire()]
--- consumes one permit and [Semaphore:release()] returns one permit. If no
--- permits are available, `acquire()` suspends the current task until another
--- task releases one.
---
--- The preferred way to use a Semaphore is with the `with()` method, which
--- automatically acquires and releases the semaphore around a function call.
--- This is useful for limiting sections that start external work and then
--- await it, such as file reads, requests, or subprocesses.
---
--- ```lua
--- local async = vim.async
---
--- async.run(function()
--- local limit = async.semaphore(4)
--- local tasks = {}
---
--- for _, path in ipairs(paths) do
--- table.insert(tasks, async.run(function()
--- return limit:with(function()
--- return read_file(path)
--- end)
--- end))
--- end
---
--- local next_task = async.iter(tasks)
--- while true do
--- local task = next_task()
--- if task == nil then
--- break
--- end
--- async.await(task)
--- end
--- end)
--- ```
--- @class vim.async.Semaphore
--- @field private _permits integer
--- @field private _max_permits integer
--- @field package _event vim.async.Event
local Semaphore = {}
Semaphore.__index = Semaphore
--- Executes a function while holding one semaphore permit.
---
--- This acquires the semaphore before running the function and releases it
--- after the function completes, even if it errors or the current task is
--- closed.
--- @async
--- @generic R
--- @param fn async fun(): R... # Function to execute within the semaphore's context.
--- @return R... # Result(s) of the executed function.
function Semaphore:with(fn)
self:acquire()
-- This pcall is only a try/finally guard for release(); all errors are
-- immediately rethrown so it is not an async recovery boundary.
local r = F.pack_len(pcall(fn))
self:release()
local stat = r[1]
if not stat then
local err = r[2]
error(err, 0)
end
return unpack(r, 2, r.n)
end
--- Acquire a semaphore permit.
---
--- If the internal counter is greater than zero, decrement it by `1` and
--- return immediately. If it is `0`, wait until [Semaphore:release()] is
--- called.
--- @async
function Semaphore:acquire()
self._event:wait()
self._permits = self._permits - 1
assert(self._permits >= 0, 'Semaphore value is negative')
if self._permits == 0 then
self._event:clear()
end
end
--- Release a semaphore permit.
---
--- Increments the internal counter by `1` and can wake a task waiting in
--- [Semaphore:acquire()].
---
--- Calling this more times than permits were acquired raises an error.
function Semaphore:release()
if self._permits >= self._max_permits then
error('Semaphore value is greater than max permits', 2)
end
self._permits = self._permits + 1
self._event:set(1)
end
--- Create an async semaphore that allows up to a given number of acquisitions.
---
--- Prefer [Semaphore:with()] for most uses so permits are released reliably.
--- Use [Semaphore:acquire()] and [Semaphore:release()] directly only when the
--- acquire and release points cannot be expressed as one function call.
--- @param permits? integer (default: 1)
--- @return vim.async.Semaphore
local function new_semaphore(permits)
validate('permits', permits, 'number', true)
permits = permits or 1
if permits < 1 or permits % 1 ~= 0 then
error('permits: expected positive integer', 2)
end
local obj = setmetatable({
_max_permits = permits,
_permits = permits,
_event = new_event(),
}, Semaphore)
obj._event:set()
return obj
end
return new_semaphore
|
