Improve PID locking wait

* Do not block on pidfile when using the version command

* Emit warnings when blocking on pid file flock.

Closes: #124

Author: mfainberg-cf

cmd/cmd.go

@@ -5,11 +5,12 @@ import (
 
 	"github.com/replicate/pget/cmd/multifile"
 	"github.com/replicate/pget/cmd/root"
+	"github.com/replicate/pget/cmd/version"
 )
 
 func GetRootCommand() *cobra.Command {
 	rootCMD := root.GetCommand()
 	rootCMD.AddCommand(multifile.GetCommand())
-	rootCMD.AddCommand(VersionCMD)
+	rootCMD.AddCommand(version.VersionCMD)
 	return rootCMD
 }

cmd/root/root.go

@@ -3,6 +3,7 @@ package root
 import (
 	"context"
 	"fmt"
+	"github.com/replicate/pget/cmd/version"
 	"os"
 	"runtime"
 	"time"
@@ -51,20 +52,25 @@ func GetCommand() *cobra.Command {
 			if err := config.PersistentStartupProcessFlags(); err != nil {
 				return err
 			}
-			pidFilePath := viper.GetString(config.OptPIDFile)
-			pid, err := cli.NewPIDFile(pidFilePath)
-			if err != nil {
-				return err
-			}
-			err = pid.Acquire()
-			if err != nil {
-				return err
+			if cmd.CalledAs() != version.VersionCMDName {
+				pidFilePath := viper.GetString(config.OptPIDFile)
+				pid, err := cli.NewPIDFile(pidFilePath)
+				if err != nil {
+					return err
+				}
+				err = pid.Acquire()
+				if err != nil {
+					return err
+				}
+				pidFile = pid
 			}
-			pidFile = pid
 			return nil
 		},
 		PersistentPostRunE: func(cmd *cobra.Command, args []string) error {
-			return pidFile.Release()
+			if pidFile != nil {
+				return pidFile.Release()
+			}
+			return nil
 		},
 		PreRun:  rootCmdPreRun,
 		RunE:    runRootCMD,

cmd/version.go renamed to cmd/version/version.go

@@ -1,4 +1,4 @@
-package cmd
+package version
 
 import (
 	"fmt"
@@ -8,8 +8,10 @@ import (
 	"github.com/replicate/pget/pkg/version"
 )
 
+const VersionCMDName = "version"
+
 var VersionCMD = &cobra.Command{
-	Use:   "version",
+	Use:   VersionCMDName,
 	Short: "print version and build information",
 	Long:  "Print the version information",
 	Run: func(cmd *cobra.Command, args []string) {

pkg/cli/pid.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"os"
 	"syscall"
+
+	"github.com/replicate/pget/pkg/logging"
 )
 
 type PIDFile struct {
@@ -22,8 +24,21 @@ func NewPIDFile(path string) (*PIDFile, error) {
 }
 
 func (p *PIDFile) Acquire() error {
+	logger := logging.GetLogger()
 	funcs := []func() error{
-		func() error { return syscall.Flock(p.fd, syscall.LOCK_EX) },
+		func() error {
+			logger.Debug().Str("blocking_lock_acquire", "false").Msg("Waiting on Lock")
+			err := syscall.Flock(p.fd, syscall.LOCK_EX|syscall.LOCK_NB)
+			if err != nil {
+				logger.Warn().
+					Err(err).
+					Str("message", "Another pget process may be running, use 'pget multifile' to download multiple files in parallel").
+					Msg("Waiting on Lock")
+				logger.Debug().Str("blocking_lock_acquire", "true").Msg("Waiting on Lock")
+				err = syscall.Flock(p.fd, syscall.LOCK_EX)
+			}
+			return err
+		},
 		p.writePID,
 		p.file.Sync,
 	}