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// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package metrics
import (
"io/fs"
"sync"
"go4.org/mem"
"tailscale.com/util/dirwalk"
)
// counter is a reusable counter for counting file descriptors.
type counter struct {
n int
// cb is the (*counter).count method value. Creating it allocates,
// so we have to save it away and use a sync.Pool to keep currentFDs
// amortized alloc-free.
cb func(name mem.RO, de fs.DirEntry) error
}
var counterPool = &sync.Pool{New: func() any {
c := new(counter)
c.cb = c.count
return c
}}
func (c *counter) count(name mem.RO, de fs.DirEntry) error {
c.n++
return nil
}
func currentFDs() int {
c := counterPool.Get().(*counter)
defer counterPool.Put(c)
c.n = 0
dirwalk.WalkShallow(mem.S("/proc/self/fd"), c.cb)
return c.n
}
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