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|
package main
import (
"fmt"
"io/ioutil"
"os"
"os/exec"
"os/signal"
"path"
"strconv"
"syscall"
"time"
"github.com/sirupsen/logrus"
"gitlab.com/gitlab-org/gitaly/internal/bootstrap"
"gitlab.com/gitlab-org/gitaly/internal/ps"
)
const (
envJSONLogging = "WRAPPER_JSON_LOGGING"
)
func main() {
if jsonLogging() {
logrus.SetFormatter(&logrus.JSONFormatter{})
}
if len(os.Args) < 2 {
logrus.Fatalf("usage: %s forking_binary [args]", os.Args[0])
}
bin, args := os.Args[1], os.Args[2:]
log := logrus.WithField("wrapper", os.Getpid()).WithField("binary", bin)
log.Info("Wrapper started")
if bootstrap.PidFile() == "" {
log.Fatalf("missing pid file ENV variable %q", bootstrap.PidFileEnvVar)
}
log.WithField("pid_file", bootstrap.PidFile()).Info("finding process")
proc, err := findProcess()
if err != nil {
log.WithError(err).Fatal("find process")
}
if proc != nil && matches(proc, bin) {
log.Info("adopting a process")
} else {
log.Info("spawning a process")
newProc, err := spawn(bin, args)
if err != nil {
log.WithError(err).Fatal("spawn process")
}
proc = newProc
}
log = log.WithField("process", proc.Pid)
log.Info("monitoring process")
forwardSignals(proc, log)
// wait
for isAlive(proc) {
time.Sleep(1 * time.Second)
}
log.Error("wrapper for process shutting down")
}
func findProcess() (*os.Process, error) {
pid, err := getPid()
if err != nil && !os.IsNotExist(err) {
return nil, err
}
// os.FindProcess on unix do not return an error if the process does not exist
process, err := os.FindProcess(pid)
if err != nil {
return nil, err
}
if isAlive(process) {
return process, nil
}
return nil, nil
}
func spawn(bin string, args []string) (*os.Process, error) {
cmd := exec.Command(bin, args...)
cmd.Env = append(os.Environ(), fmt.Sprintf("%s=true", bootstrap.UpgradesEnabledEnvVar))
cmd.Stdin = os.Stdin
cmd.Stdout = os.Stdout
cmd.Stderr = os.Stderr
if err := cmd.Start(); err != nil {
return nil, err
}
// This cmd.Wait() is crucial. Without it we cannot detect if the command we just spawned has crashed.
go cmd.Wait()
return cmd.Process, nil
}
func forwardSignals(proc *os.Process, log *logrus.Entry) {
sigs := make(chan os.Signal, 1)
go func() {
for sig := range sigs {
log.WithField("signal", sig).Warning("forwarding signal")
if err := proc.Signal(sig); err != nil {
log.WithField("signal", sig).WithError(err).Error("can't forward the signal")
}
}
}()
signal.Notify(sigs)
}
func getPid() (int, error) {
data, err := ioutil.ReadFile(bootstrap.PidFile())
if err != nil {
return 0, err
}
return strconv.Atoi(string(data))
}
func isAlive(p *os.Process) bool {
// After p exits, and after it gets reaped, this p.Signal will fail. It is crucial that p gets reaped.
// If p was spawned by the current process, it will get reaped from a goroutine that does cmd.Wait().
// If p was spawned by someone else we rely on them to reap it, or on p to become an orphan.
// In the orphan case p should get reaped by the OS (PID 1).
return p.Signal(syscall.Signal(0)) == nil
}
func matches(p *os.Process, bin string) bool {
command, err := ps.Comm(p.Pid)
if err != nil {
return false
}
if path.Base(command) == path.Base(bin) {
return true
}
return false
}
func jsonLogging() bool {
return os.Getenv(envJSONLogging) == "true"
}
|
