rlimit_unix.go

     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
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