Implement the 'shared' subcommand for mmutex

mmutex/cmd/mmutex/exclusive.go

Index: mmutex/cmd/mmutex/exclusive.go
diff --git a/mmutex/cmd/mmutex/exclusive.go b/mmutex/cmd/mmutex/exclusive.go
index 00ff24d6e694ec1206be158578886e8c09df413e..dd799fb2d8f28516594de0bf15b32fe102e0bdc3 100644
--- a/mmutex/cmd/mmutex/exclusive.go
+++ b/mmutex/cmd/mmutex/exclusive.go
@@ -27,12 +27,12 @@ import (
 )
 
 var cmdExclusive = &subcommands.Command{
-	UsageLine: "exclusive -- <command>",
+	UsageLine: "exclusive [options] -- <command>",
 	ShortDesc: "acquires an exclusive lock before running the command",
 	CommandRun: func() subcommands.CommandRun {
 		c := &cmdExclusiveRun{}
-		c.Flags.DurationVar(&c.fslockTimeout, "fslock-timeout", 0, "Lock acquisition timeout")
-		c.Flags.DurationVar(&c.fslockPollingInterval, "fslock-polling-interval", 0, "Lock acquisition polling interval")
+		c.Flags.DurationVar(&c.fslockTimeout, "fslock-timeout", 2*time.Hour, "Lock acquisition timeout")
+		c.Flags.DurationVar(&c.fslockPollingInterval, "fslock-polling-interval", 5*time.Second, "Lock acquisition polling interval")
 		return c
 	},
 }
@@ -45,6 +45,11 @@ type cmdExclusiveRun struct {
 
 func (c *cmdExclusiveRun) Run(a subcommands.Application, args []string, env subcommands.Env) int {
 	if err := RunExclusive(args, c.fslockTimeout, c.fslockPollingInterval); err != nil {
+		if exitErr, ok := err.(*exec.ExitError); ok {
+			return lib.GetExitCode(exitErr)
+		}
+
+		// We encountered an error that's unrelated to the command itself.
 		fmt.Fprintln(os.Stderr, err)
 		return 1
 	} else {