vpython: Add VirtualEnv creation package.

vpython/venv/system_posix.go

+// Copyright 2017 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// +build darwin linux freebsd netbsd openbsd android
+
+package venv
+
+import (
+        "os"
+        "path/filepath"
+        "syscall"
+
+        "github.com/luci/luci-go/common/errors"
+)
+
+// longestGeneratedScriptPath returns the path of the longest generated script
+// given a VirtualEnv root.
+func longestGeneratedScriptPath(baseDir string) string {
+        return venvBinPath(baseDir, "python-config")
+}
+
+// venvBinPath resolves the path to a VirtualEnv binary.
+func venvBinPath(root, name string) string {
+        return filepath.Join(root, "bin", name)
+}
+
+func checkProcessRunning(pid int) error {
+        proc, err := os.FindProcess(pid)
+        if err != nil {
+                return errors.Annotate(err).Reason("failed to find process").Err()
+        }
+
+        if err := proc.Signal(os.Signal(syscall.Signal(0))); err != nil {
+                return errors.Annotate(err).Reason("failed to signal process").Err()
+        }
+        return nil
+}