| // Copyright 2011 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| //go:build aix || darwin || dragonfly || freebsd || linux || netbsd || openbsd || solaris |
| |
| package net |
| |
| import ( |
| "syscall" |
| ) |
| |
| // concurrentThreadsLimit returns the number of threads we permit to |
| // run concurrently doing DNS lookups via cgo. A DNS lookup may use a |
| // file descriptor so we limit this to less than the number of |
| // permitted open files. On some systems, notably Darwin, if |
| // getaddrinfo is unable to open a file descriptor it simply returns |
| // EAI_NONAME rather than a useful error. Limiting the number of |
| // concurrent getaddrinfo calls to less than the permitted number of |
| // file descriptors makes that error less likely. We don't bother to |
| // apply the same limit to DNS lookups run directly from Go, because |
| // there we will return a meaningful "too many open files" error. |
| func concurrentThreadsLimit() int { |
| var rlim syscall.Rlimit |
| if err := syscall.Getrlimit(syscall.RLIMIT_NOFILE, &rlim); err != nil { |
| return 500 |
| } |
| r := int(rlim.Cur) |
| if r > 500 { |
| r = 500 |
| } else if r > 30 { |
| r -= 30 |
| } |
| return r |
| } |