[337] Add logic to run child processes nicer than parent

go.mod

@@ -17,6 +17,7 @@ require (
 	github.com/stretchr/testify v1.11.1
 	golang.org/x/net v0.52.0
 	gopkg.in/yaml.v2 v2.4.0
+	github.com/hekmon/processpriority v1.0.0
 )
 
 require (

go.sum

@@ -45,6 +45,8 @@ github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
 github.com/google/pprof v0.0.0-20260302011040-a15ffb7f9dcc h1:VBbFa1lDYWEeV5FZKUiYKYT0VxCp9twUmmaq9eb8sXw=
 github.com/google/pprof v0.0.0-20260302011040-a15ffb7f9dcc/go.mod h1:MxpfABSjhmINe3F1It9d+8exIHFvUqtLIRCdOGNXqiI=
+github.com/hekmon/processpriority v1.0.0 h1:Qj0P8iEO25b+8wGQ1ZG7HzBLpHjGGSgbujr++dSBn68=
+github.com/hekmon/processpriority v1.0.0/go.mod h1:pZm/iZaUiyJpxD7Ad+gGAP3jusrALui1hXL9t7twP6M=
 github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
 github.com/jessevdk/go-flags v1.6.1 h1:Cvu5U8UGrLay1rZfv/zP7iLpSHGUZ/Ou68T0iX1bBK4=
 github.com/jessevdk/go-flags v1.6.1/go.mod h1:Mk8T1hIAWpOiJiHa9rJASDK2UGWji0EuPGBnNLMooyc=

system/cmd_runner_interface.go

@@ -18,6 +18,9 @@ type Command struct {
 	// Don't echo stdout/stderr
 	Quiet bool
 
+	// Run command with a priority lower than the parent process
+	SpawnWithLowerPriority bool
+
 	Stdin io.Reader
 
 	// Full stdout and stderr will be captured to memory

system/exec_cmd_runner.go

@@ -3,9 +3,11 @@ package system
 import (
 	"os"
 	"os/exec"
+	"runtime"
 	"strings"
 
 	boshlog "github.com/cloudfoundry/bosh-utils/logger"
+	"github.com/hekmon/processpriority"
 )
 
 type execCmdRunner struct {
@@ -16,6 +18,35 @@ func NewExecCmdRunner(logger boshlog.Logger) CmdRunner {
 	return execCmdRunner{logger}
 }
 
+func (r execCmdRunner) LowerProcessPriority(processPid int) error {
+	parentName := os.Args[0]
+	parentPid := os.Getpid()
+
+	parentPrio, rawParentPrio, err := processpriority.Get(parentPid)
+	if err != nil {
+		r.logger.Debug(parentName, "Error getting priority of the current process (%d): %s", parentPid, err)
+		return err
+	}
+	r.logger.Debug(parentName, "Current process priority is %s (%d)", parentPrio, rawParentPrio)
+
+	if runtime.GOOS == "windows" {
+		r.logger.Debug(parentName, "Setting new child process priority to IDLE")
+		err = processpriority.Set(processPid, processpriority.Idle)
+	} else {
+		processPrio := rawParentPrio + 5
+		if processPrio > 19 {
+			processPrio = 19
+		}
+		r.logger.Debug(parentName, "Setting new child process priority to %d", processPrio)
+		err = processpriority.SetRAW(processPid, processPrio)
+	}
+
+	if err != nil {
+		r.logger.Error(parentName, "Error setting priority on the command: %s", err)
+	}
+	return err
+}
+
 func (r execCmdRunner) RunComplexCommand(cmd Command) (string, string, int, error) {
 	process := NewExecProcess(r.buildComplexCommand(cmd), cmd.KeepAttached, cmd.Quiet, r.logger)
 
@@ -24,6 +55,12 @@ func (r execCmdRunner) RunComplexCommand(cmd Command) (string, string, int, erro
 		return "", "", -1, err
 	}
 
+	if cmd.SpawnWithLowerPriority {
+		if err := r.LowerProcessPriority(process.cmd.Process.Pid); err != nil {
+			r.logger.Error(cmd.Name, "Error setting process priority on %s", cmd.Name)
+		}
+	}
+
 	result := <-process.Wait()
 
 	return result.Stdout, result.Stderr, result.ExitStatus, result.Error

system/exec_cmd_runner_test.go

@@ -13,6 +13,8 @@ import (
 	"github.com/cloudfoundry/bosh-utils/logger/loggerfakes"
 	. "github.com/cloudfoundry/bosh-utils/system"
 	fakesys "github.com/cloudfoundry/bosh-utils/system/fakes"
+
+	"github.com/hekmon/processpriority"
 )
 
 const ErrExitCode = 14
@@ -180,6 +182,35 @@ var _ = Describe("execCmdRunner", func() {
 				Expect(envVars).To(HaveKeyWithValue("ABC", "XYZ"))
 				Expect(envVars).To(HaveKeyWithValue("abc", "xyz"))
 			})
+
+			It("runs a command nicer than itself", func() {
+				// Write script that echos the its nice value
+				script := "#!/bin/bash\nnice\n"
+				tmpFile, err := os.CreateTemp("", "tmp-script-*.sh")
+				Expect(err).ToNot(HaveOccurred())
+				defer os.Remove(tmpFile.Name())
+				_, err = tmpFile.WriteString(script)
+				Expect(err).ToNot(HaveOccurred())
+				err = tmpFile.Close()
+				Expect(err).ToNot(HaveOccurred())
+				err = os.Chmod(tmpFile.Name(), 0700)
+				Expect(err).ToNot(HaveOccurred())
+
+				parentPid := os.Getpid()
+				_, rawParentPrio, err := processpriority.Get(parentPid)
+				Expect(err).ToNot(HaveOccurred())
+				expectedOutput := fmt.Sprintf("%d\n", rawParentPrio+5)
+
+				// Run script with SpawnWithLowerPriority
+				cmd := Command{
+					Name:                   tmpFile.Name(),
+					SpawnWithLowerPriority: true,
+				}
+				stdout, _, _, err := runner.RunComplexCommand(cmd)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(stdout).To(Equal(expectedOutput))
+			})
 		})
 
 		Context("windows specific behavior", func() {
@@ -247,6 +278,32 @@ var _ = Describe("execCmdRunner", func() {
 				Expect(envVars).ToNot(HaveKey("_bar"))
 				Expect(envVars).To(HaveKeyWithValue("_BAR", "alpha=first"))
 			})
+
+			It("runs a command nicer than itself", func() {
+				// Write script that echos the its nice value
+				script := "$proc = Get-Process -Id $PID\nWrite-Output $proc.PriorityClass"
+
+				tmpFile, err := os.CreateTemp("", "tmp-script-*.ps1")
+				Expect(err).ToNot(HaveOccurred())
+				defer os.Remove(tmpFile.Name())
+				_, err = tmpFile.WriteString(script)
+				Expect(err).ToNot(HaveOccurred())
+				err = tmpFile.Close()
+				Expect(err).ToNot(HaveOccurred())
+				err = os.Chmod(tmpFile.Name(), 0700)
+				Expect(err).ToNot(HaveOccurred())
+
+				// Run script with SpawnWithLowerPriority
+				cmd := Command{
+					Name:                   "powershell",
+					Args:                   []string{"-ExecutionPolicy", "Bypass", "-File", tmpFile.Name()},
+					SpawnWithLowerPriority: true,
+				}
+				stdout, _, _, err := runner.RunComplexCommand(cmd)
+
+				Expect(err).ToNot(HaveOccurred())
+				Expect(stdout).To(Equal("Idle\r\n"))
+			})
 		})
 
 		It("run complex command with stdin", func() {