refactor(util): reuse timer handles in Debouncer

lua/git.lua

@@ -1,4 +1,3 @@
-local log = require("log")
 local util = require("util")
 
 local HIGHLIGHTS = {
@@ -97,21 +96,13 @@ local Repo = {}
 Repo.__index = Repo
 
 function Repo:start_watcher()
-    local watcher, err_msg, err_name = vim.uv.new_fs_event()
+    local watcher = assert(vim.uv.new_fs_event())
-    if not watcher then
+    assert(watcher:start(self.gitdir, {}, function(err, filename)
-        log.error(
-            "Failed to create fs event watcher: %s (%s)",
-            err_msg,
-            err_name
-        )
-        return
-    end
-    watcher:start(self.gitdir, {}, function(err, filename)
         if err or (filename ~= "index" and filename ~= "HEAD") then
             return
         end
         self.refresh:call()
-    end)
+    end))
     self.watcher = watcher
 end
 

lua/pack.lua

@@ -187,17 +187,7 @@ function M.watch()
 
     local plugins_dir = vim.fs.joinpath(config_dir, "plugins")
 
-    local err_msg, err_name
+    watcher = assert(vim.uv.new_fs_event())
-    watcher, err_msg, err_name = vim.uv.new_fs_event()
-    if not watcher then
-        log.error(
-            "Failed to create fs event watcher: %s (%s)",
-            err_msg,
-            err_name
-        )
-        return
-    end
-
     reload = util.debounce(function(filename)
         local path = vim.fs.joinpath(plugins_dir, filename)
         if not vim.uv.fs_stat(path) then
@@ -211,7 +201,7 @@ function M.watch()
         end
     end, 100)
 
-    watcher:start(plugins_dir, {}, function(err, filename)
+    assert(watcher:start(plugins_dir, {}, function(err, filename)
         if err then
             log.error("Watch error: %s", err)
             return
@@ -220,7 +210,7 @@ function M.watch()
             return
         end
         reload:call(filename)
-    end)
+    end))
 end
 
 function M.unwatch()

lua/util.lua

@@ -295,10 +295,16 @@ end
 
 local NIL_KEY = {}
 
+---@class ow.Util.Debouncer.Slot
+---@field timer uv.uv_timer_t
+---@field cb function
+---@field id any
+---@field args table
+
 ---@class ow.Util.Debouncer
 ---@field private _fn fun(id: any, ...)
 ---@field private _delay integer
----@field private _timers table<any, uv.uv_timer_t>
+---@field private _slots table<any, ow.Util.Debouncer.Slot>
 local Debouncer = {}
 Debouncer.__index = Debouncer
 
@@ -306,42 +312,73 @@ Debouncer.__index = Debouncer
 ---@param delay integer
 ---@return ow.Util.Debouncer
 function Debouncer.new(fn, delay)
-    return setmetatable({ _fn = fn, _delay = delay, _timers = {} }, Debouncer)
+    return setmetatable({ _fn = fn, _delay = delay, _slots = {} }, Debouncer)
+end
+
+---@param slot ow.Util.Debouncer.Slot
+local function dispose(slot)
+    if not slot.timer:is_closing() then
+        slot.timer:stop()
+        slot.timer:close()
+    end
 end
 
 ---@param id? any
 ---@param ... any
 function Debouncer:call(id, ...)
     local key = id == nil and NIL_KEY or id
+    local slot = self._slots[key]
     local args = vim.F.pack_len(...)
-    self:cancel(id)
+    if not slot then
-    self._timers[key] = vim.defer_fn(function()
+        -- cb lives on the slot so restart (the else branch below) can hand
-        self._timers[key] = nil
+        -- the same closure back to timer:start, avoiding a fresh
-        self._fn(id, vim.F.unpack_len(args))
+        -- schedule_wrap allocation per call. It reads id/args from the
-    end, self._delay)
+        -- slot (not upvalues) so restarts pick up the latest args.
+        local timer = assert(vim.uv.new_timer())
+        ---@type ow.Util.Debouncer.Slot
+        local new_slot
+        new_slot = {
+            timer = timer,
+            id = id,
+            args = args,
+            cb = vim.schedule_wrap(function()
+                -- Slot may have been cancelled between libuv firing and
+                -- this scheduled callback running. Identity-check before
+                -- firing.
+                if self._slots[key] ~= new_slot then
+                    return
                 end
-
+                self._slots[key] = nil
----@param timer uv.uv_timer_t
+                dispose(new_slot)
-local function dispose(timer)
+                self._fn(new_slot.id, vim.F.unpack_len(new_slot.args))
-    timer:stop()
+            end),
-    timer:close()
+        }
+        self._slots[key] = new_slot
+        slot = new_slot
+    else
+        slot.id = id
+        slot.args = args
+    end
+    -- uv_timer_start on an already-active timer restarts it with the new
+    -- timeout, reusing the same handle (no per-call allocation).
+    assert(slot.timer:start(self._delay, 0, slot.cb))
 end
 
 ---@param id? any
 function Debouncer:cancel(id)
     local key = id == nil and NIL_KEY or id
-    local timer = self._timers[key]
+    local slot = self._slots[key]
-    if timer then
+    if slot then
-        dispose(timer)
+        self._slots[key] = nil
-        self._timers[key] = nil
+        dispose(slot)
     end
 end
 
 function Debouncer:cancel_all()
-    for _, t in pairs(self._timers) do
+    for _, slot in pairs(self._slots) do
-        dispose(t)
+        dispose(slot)
     end
-    self._timers = {}
+    self._slots = {}
 end
 
 Util.Debouncer = Debouncer