1 // Copyright 2023 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4 5 //go:build unix || wasip1
6 7 package net
8 9 import "syscall"
10 11 // concurrentThreadsLimit returns the number of threads we permit to
12 // run concurrently doing DNS lookups via cgo. A DNS lookup may use a
13 // file descriptor so we limit this to less than the number of
14 // permitted open files. On some systems, notably Darwin, if
15 // getaddrinfo is unable to open a file descriptor it simply returns
16 // EAI_NONAME rather than a useful error. Limiting the number of
17 // concurrent getaddrinfo calls to less than the permitted number of
18 // file descriptors makes that error less likely. We don't bother to
19 // apply the same limit to DNS lookups run directly from Go, because
20 // there we will return a meaningful "too many open files" error.
21 func concurrentThreadsLimit() int {
22 var rlim syscall.Rlimit
23 if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rlim); err != nil {
24 return 500
25 }
26 r := rlim.Cur
27 if r > 500 {
28 r = 500
29 } else if r > 30 {
30 r -= 30
31 }
32 return int(r)
33 }
34