rlimit.go

     1  // Copyright 2022 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
     6  
     7  package syscall
     8  
     9  import (
    10  	"sync/atomic"
    11  )
    12  
    13  // origRlimitNofile, if non-nil, is the original soft RLIMIT_NOFILE.
    14  var origRlimitNofile atomic.Pointer[Rlimit]
    15  
    16  // Some systems set an artificially low soft limit on open file count, for compatibility
    17  // with code that uses select and its hard-coded maximum file descriptor
    18  // (limited by the size of fd_set).
    19  //
    20  // Go does not use select, so it should not be subject to these limits.
    21  // On some systems the limit is 256, which is very easy to run into,
    22  // even in simple programs like gofmt when they parallelize walking
    23  // a file tree.
    24  //
    25  // After a long discussion on go.dev/issue/46279, we decided the
    26  // best approach was for Go to raise the limit unconditionally for itself,
    27  // and then leave old software to set the limit back as needed.
    28  // Code that really wants Go to leave the limit alone can set the hard limit,
    29  // which Go of course has no choice but to respect.
    30  func init() {
    31  	var lim Rlimit
    32  	if err := Getrlimit(RLIMIT_NOFILE, &lim); err == nil && lim.Max > 0 && lim.Cur < lim.Max-1 {
    33  		origRlimitNofile.Store(&lim)
    34  		nlim := lim
    35  
    36  		// We set Cur to Max - 1 so that we are more likely to
    37  		// detect cases where another process uses prlimit
    38  		// to change our resource limits. The theory is that
    39  		// using prlimit to change to Cur == Max is more likely
    40  		// than using prlimit to change to Cur == Max - 1.
    41  		// The place we check for this is in exec_linux.go.
    42  		nlim.Cur = nlim.Max - 1
    43  
    44  		adjustFileLimit(&nlim)
    45  		setrlimit(RLIMIT_NOFILE, &nlim)
    46  	}
    47  }
    48  
    49  func Setrlimit(resource int, rlim *Rlimit) error {
    50  	if resource == RLIMIT_NOFILE {
    51  		// Store nil in origRlimitNofile to tell StartProcess
    52  		// to not adjust the rlimit in the child process.
    53  		origRlimitNofile.Store(nil)
    54  	}
    55  	return setrlimit(resource, rlim)
    56  }
    57
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