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process.go
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process.go
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package process
// Logic for this file is largely based on:
// https://github.com/jarib/childprocess/blob/783f7a00a1678b5d929062564ef5ae76822dfd62/lib/childprocess/unix/process.rb
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"os"
"os/exec"
"regexp"
"runtime"
"strconv"
"sync"
"sync/atomic"
"syscall"
"time"
"github.com/buildkite/agent/logger"
)
type Process struct {
Pid int
PTY bool
Timestamp bool
Script []string
Env []string
ExitStatus string
buffer outputBuffer
command *exec.Cmd
// This callback is called when the process offically starts
StartCallback func()
// For every line in the process output, this callback will be called
// with the contents of the line if its filter returns true.
LineCallback func(string)
LinePreProcessor func(string) string
LineCallbackFilter func(string) bool
// Running is stored as an int32 so we can use atomic operations to
// set/get it (it's accessed by multiple goroutines)
running int32
}
// If you change header parsing here make sure to change it in the
// buildkite.com frontend logic, too
var headerExpansionRegex = regexp.MustCompile("^(?:\\^\\^\\^\\s+\\+\\+\\+)\\s*$")
func (p *Process) Start() error {
p.command = exec.Command(p.Script[0], p.Script[1:]...)
// Copy the current processes ENV and merge in the new ones. We do this
// so the sub process gets PATH and stuff. We merge our path in over
// the top of the current one so the ENV from Buildkite and the agent
// take precedence over the agent
currentEnv := os.Environ()
p.command.Env = append(currentEnv, p.Env...)
var waitGroup sync.WaitGroup
lineReaderPipe, lineWriterPipe := io.Pipe()
var multiWriter io.Writer
if p.Timestamp {
multiWriter = io.MultiWriter(lineWriterPipe)
} else {
multiWriter = io.MultiWriter(&p.buffer, lineWriterPipe)
}
// Toggle between running in a pty
if p.PTY {
pty, err := StartPTY(p.command)
if err != nil {
p.ExitStatus = "1"
return err
}
p.Pid = p.command.Process.Pid
p.setRunning(true)
waitGroup.Add(1)
go func() {
logger.Debug("[Process] Starting to copy PTY to the buffer")
// Copy the pty to our buffer. This will block until it
// EOF's or something breaks.
_, err = io.Copy(multiWriter, pty)
if e, ok := err.(*os.PathError); ok && e.Err == syscall.EIO {
// We can safely ignore this error, because
// it's just the PTY telling us that it closed
// successfully. See:
// https://github.com/buildkite/agent/pull/34#issuecomment-46080419
err = nil
}
if err != nil {
logger.Error("[Process] PTY output copy failed with error: %T: %v", err, err)
} else {
logger.Debug("[Process] PTY has finished being copied to the buffer")
}
waitGroup.Done()
}()
} else {
p.command.Stdout = multiWriter
p.command.Stderr = multiWriter
p.command.Stdin = nil
err := p.command.Start()
if err != nil {
p.ExitStatus = "1"
return err
}
p.Pid = p.command.Process.Pid
p.setRunning(true)
}
logger.Info("[Process] Process is running with PID: %d", p.Pid)
// Add the line callback routine to the waitGroup
waitGroup.Add(1)
go func() {
logger.Debug("[LineScanner] Starting to read lines")
reader := bufio.NewReader(lineReaderPipe)
var appending []byte
var lineCallbackWaitGroup sync.WaitGroup
for {
line, isPrefix, err := reader.ReadLine()
if err != nil {
if err == io.EOF {
logger.Debug("[LineScanner] Encountered EOF")
break
}
logger.Error("[LineScanner] Failed to read: (%T: %v)", err, err)
}
// If isPrefix is true, that means we've got a really
// long line incoming, and we'll keep appending to it
// until isPrefix is false (which means the long line
// has ended.
if isPrefix && appending == nil {
logger.Debug("[LineScanner] Line is too long to read, going to buffer it until it finishes")
// bufio.ReadLine returns a slice which is only valid until the next invocation
// since it points to its own internal buffer array. To accumulate the entire
// result we make a copy of the first prefix, and insure there is spare capacity
// for future appends to minimize the need for resizing on append.
appending = make([]byte, len(line), (cap(line))*2)
copy(appending, line)
continue
}
// Should we be appending?
if appending != nil {
appending = append(appending, line...)
// No more isPrefix! Line is finished!
if !isPrefix {
logger.Debug("[LineScanner] Finished buffering long line")
line = appending
// Reset appending back to nil
appending = nil
} else {
continue
}
}
// If we're timestamping this main thread will take
// the hit of running the regex so we can build up
// the timestamped buffer without breaking headers,
// otherwise we let the goroutines take the perf hit.
checkedForCallback := false
lineHasCallback := false
lineString := p.LinePreProcessor(string(line))
// Create the prefixed buffer
if p.Timestamp {
lineHasCallback = p.LineCallbackFilter(lineString)
checkedForCallback = true
if lineHasCallback || headerExpansionRegex.MatchString(lineString) {
// Don't timestamp special lines (e.g. header)
p.buffer.WriteString(fmt.Sprintf("%s\n", line))
} else {
currentTime := time.Now().UTC().Format(time.RFC3339)
p.buffer.WriteString(fmt.Sprintf("[%s] %s\n", currentTime, line))
}
}
if lineHasCallback || !checkedForCallback {
lineCallbackWaitGroup.Add(1)
go func(line string) {
defer lineCallbackWaitGroup.Done()
if (checkedForCallback && lineHasCallback) || p.LineCallbackFilter(lineString) {
p.LineCallback(line)
}
}(lineString)
}
}
// We need to make sure all the line callbacks have finish before
// finish up the process
logger.Debug("[LineScanner] Waiting for callbacks to finish")
lineCallbackWaitGroup.Wait()
logger.Debug("[LineScanner] Finished")
waitGroup.Done()
}()
// Call the StartCallback
go p.StartCallback()
// Wait until the process has finished. The returned error is nil if the command runs,
// has no problems copying stdin, stdout, and stderr, and exits with a zero exit status.
waitResult := p.command.Wait()
// Close the line writer pipe
lineWriterPipe.Close()
// The process is no longer running at this point
p.setRunning(false)
// Find the exit status of the script
p.ExitStatus = getExitStatus(waitResult)
logger.Info("Process with PID: %d finished with Exit Status: %s", p.Pid, p.ExitStatus)
// Sometimes (in docker containers) io.Copy never seems to finish. This is a mega
// hack around it. If it doesn't finish after 1 second, just continue.
logger.Debug("[Process] Waiting for routines to finish")
err := timeoutWait(&waitGroup)
if err != nil {
logger.Debug("[Process] Timed out waiting for wait group: (%T: %v)", err, err)
}
// No error occurred so we can return nil
return nil
}
func (p *Process) Output() string {
return p.buffer.String()
}
func (p *Process) Kill() error {
var err error
if runtime.GOOS == "windows" {
// Sending Interrupt on Windows is not implemented.
// https://golang.org/src/os/exec.go?s=3842:3884#L110
err = exec.Command("CMD", "/C", "TASKKILL", "/F", "/T", "/PID", strconv.Itoa(p.Pid)).Run()
} else {
// Send a sigterm
err = p.signal(syscall.SIGTERM)
}
if err != nil {
return err
}
// Make a channel that we'll use as a timeout
c := make(chan int, 1)
checking := true
// Start a routine that checks to see if the process
// is still alive.
go func() {
for checking {
logger.Debug("[Process] Checking to see if PID: %d is still alive", p.Pid)
foundProcess, err := os.FindProcess(p.Pid)
// Can't find the process at all
if err != nil {
logger.Debug("[Process] Could not find process with PID: %d", p.Pid)
break
}
// We have some information about the process
if foundProcess != nil {
processState, err := foundProcess.Wait()
if err != nil || processState.Exited() {
logger.Debug("[Process] Process with PID: %d has exited.", p.Pid)
break
}
}
// Retry in a moment
sleepTime := time.Duration(1 * time.Second)
time.Sleep(sleepTime)
}
c <- 1
}()
// Timeout this process after 3 seconds
select {
case _ = <-c:
// Was successfully terminated
case <-time.After(10 * time.Second):
// Stop checking in the routine above
checking = false
// Forcefully kill the thing
err = p.signal(syscall.SIGKILL)
if err != nil {
return err
}
}
return nil
}
func (p *Process) signal(sig os.Signal) error {
if p.command != nil && p.command.Process != nil {
logger.Debug("[Process] Sending signal: %s to PID: %d", sig.String(), p.Pid)
err := p.command.Process.Signal(sig)
if err != nil {
logger.Error("[Process] Failed to send signal: %s to PID: %d (%T: %v)", sig.String(), p.Pid, err, err)
return err
}
} else {
logger.Debug("[Process] No process to signal yet")
}
return nil
}
// Returns whether or not the process is running
func (p *Process) IsRunning() bool {
return atomic.LoadInt32(&p.running) != 0
}
// Sets the running flag of the process
func (p *Process) setRunning(r bool) {
// Use the atomic package to avoid race conditions when setting the
// `running` value from multiple routines
if r {
atomic.StoreInt32(&p.running, 1)
} else {
atomic.StoreInt32(&p.running, 0)
}
}
// https://github.com/hnakamur/commango/blob/fe42b1cf82bf536ce7e24dceaef6656002e03743/os/executil/executil.go#L29
// TODO: Can this be better?
func getExitStatus(waitResult error) string {
exitStatus := -1
if waitResult != nil {
if err, ok := waitResult.(*exec.ExitError); ok {
if s, ok := err.Sys().(syscall.WaitStatus); ok {
exitStatus = s.ExitStatus()
} else {
logger.Error("[Process] Unimplemented for system where exec.ExitError.Sys() is not syscall.WaitStatus.")
}
} else {
logger.Error("[Process] Unexpected error type in getExitStatus: %#v", waitResult)
}
} else {
exitStatus = 0
}
return fmt.Sprintf("%d", exitStatus)
}
func timeoutWait(waitGroup *sync.WaitGroup) error {
// Make a chanel that we'll use as a timeout
c := make(chan int, 1)
// Start waiting for the routines to finish
go func() {
waitGroup.Wait()
c <- 1
}()
select {
case _ = <-c:
return nil
case <-time.After(10 * time.Second):
return errors.New("Timeout")
}
return nil
}
// outputBuffer is a goroutine safe bytes.Buffer
type outputBuffer struct {
sync.RWMutex
buf bytes.Buffer
}
// Write appends the contents of p to the buffer, growing the buffer as needed. It returns
// the number of bytes written.
func (ob *outputBuffer) Write(p []byte) (n int, err error) {
ob.Lock()
defer ob.Unlock()
return ob.buf.Write(p)
}
// WriteString appends the contents of s to the buffer, growing the buffer as needed. It returns
// the number of bytes written.
func (ob *outputBuffer) WriteString(s string) (n int, err error) {
return ob.Write([]byte(s))
}
// String returns the contents of the unread portion of the buffer
// as a string. If the Buffer is a nil pointer, it returns "<nil>".
func (ob *outputBuffer) String() string {
ob.RLock()
defer ob.RUnlock()
return ob.buf.String()
}