c/os: Setrlimit/Getrlimit

internal/lib/syscall/rlimit.go

@@ -0,0 +1,52 @@
+// Copyright 2022 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 unix
+
+package syscall
+
+import (
+	"sync/atomic"
+
+	"github.com/goplus/llgo/c/syscall"
+)
+
+// origRlimitNofile, if not {0, 0}, is the original soft RLIMIT_NOFILE.
+// When we can assume that we are bootstrapping with Go 1.19,
+// this can be atomic.Pointer[Rlimit].
+var origRlimitNofile atomic.Value // of Rlimit
+
+// Some systems set an artificially low soft limit on open file count, for compatibility
+// with code that uses select and its hard-coded maximum file descriptor
+// (limited by the size of fd_set).
+//
+// Go does not use select, so it should not be subject to these limits.
+// On some systems the limit is 256, which is very easy to run into,
+// even in simple programs like gofmt when they parallelize walking
+// a file tree.
+//
+// After a long discussion on go.dev/issue/46279, we decided the
+// best approach was for Go to raise the limit unconditionally for itself,
+// and then leave old software to set the limit back as needed.
+// Code that really wants Go to leave the limit alone can set the hard limit,
+// which Go of course has no choice but to respect.
+func init() {
+	var lim Rlimit
+	if err := Getrlimit(syscall.RLIMIT_NOFILE, &lim); err == nil && lim.Cur != lim.Max {
+		origRlimitNofile.Store(lim)
+		lim.Cur = lim.Max
+		adjustFileLimit(&lim)
+		setrlimit(syscall.RLIMIT_NOFILE, &lim)
+	}
+}
+
+func Setrlimit(resource int, rlim *Rlimit) error {
+	err := setrlimit(resource, rlim)
+	if err == nil && resource == syscall.RLIMIT_NOFILE {
+		// Store zeroes in origRlimitNofile to tell StartProcess
+		// to not adjust the rlimit in the child process.
+		origRlimitNofile.Store(Rlimit{0, 0})
+	}
+	return err
+}