TUN-4356: Set AUTOMAXPROCS to the CPU limit when running in a Linux container

vendor/go.uber.org/automaxprocs/internal/cgroups/cgroup.go

@@ -0,0 +1,78 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+// +build linux
+
+package cgroups
+
+import (
+	"bufio"
+	"io"
+	"os"
+	"path/filepath"
+	"strconv"
+)
+
+// CGroup represents the data structure for a Linux control group.
+type CGroup struct {
+	path string
+}
+
+// NewCGroup returns a new *CGroup from a given path.
+func NewCGroup(path string) *CGroup {
+	return &CGroup{path: path}
+}
+
+// Path returns the path of the CGroup*.
+func (cg *CGroup) Path() string {
+	return cg.path
+}
+
+// ParamPath returns the path of the given cgroup param under itself.
+func (cg *CGroup) ParamPath(param string) string {
+	return filepath.Join(cg.path, param)
+}
+
+// readFirstLine reads the first line from a cgroup param file.
+func (cg *CGroup) readFirstLine(param string) (string, error) {
+	paramFile, err := os.Open(cg.ParamPath(param))
+	if err != nil {
+		return "", err
+	}
+	defer paramFile.Close()
+
+	scanner := bufio.NewScanner(paramFile)
+	if scanner.Scan() {
+		return scanner.Text(), nil
+	}
+	if err := scanner.Err(); err != nil {
+		return "", err
+	}
+	return "", io.ErrUnexpectedEOF
+}
+
+// readInt parses the first line from a cgroup param file as int.
+func (cg *CGroup) readInt(param string) (int, error) {
+	text, err := cg.readFirstLine(param)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.Atoi(text)
+}