Fix file lock issue on windows

[anujc25]

What this PR does / why we need it

Background:

• As part of Update the file locking module dependency #200 we switched to use github.com/alexflint/go-filemutex package instead of github.com/juju/fslock.
• The Unlock function between the two libraries behaves differently. The main difference is the go-filemutex.Unlock does not close the file whereas the fslock.Unlock does close the file, automatically releasing any acquired lock.
• Because of the above difference we noticed that when the following sequence of operations are performed the acquiring the lock fails because the file was kept open by the first lock call.
  • go-filemutex.Lock
  • go-filemutex.Unlock
  • fslock.Lock
• The above behavior can be noticed when the Tanzu CLI uses go-filemutex to lock the file using newer version of tanzu-plugin-runtime and plugins use fslock to lock the file using an older version of tanzu-plugin-runtime

Fix:

• Instead of using go-filemutex.Unlock use go-filemutex.Close to unlock the file and close the file descriptor. Doing this will make the newer version of library using go-filemutex compatible with older version of library which uses fslock

Which issue(s) this PR fixes

Fixes #

Describe testing done for PR

• Manual tests using a custom code that uses both libraries together.

// Copyright 2022 VMware, Inc. All Rights Reserved.
// SPDX-License-Identifier: Apache-2.0

package main

import (
	"os"

	"github.com/anujc/test-locking/filemutex"
	"github.com/anujc/test-locking/juju"
)

func main() {
	if len(os.Args) < 2 {
		panic("argument is required. Values: '1' or '2'")
	}

	arg := os.Args[1]
	if arg == "1" {
		filemutex.AcquireLock()
		filemutex.ReleaseLock()

		juju.AcquireLock()
		juju.ReleaseLock()

	} else if arg == "2" {
		juju.AcquireLock()
		juju.ReleaseLock()

		filemutex.AcquireLock()
		filemutex.ReleaseLock()
	} else {
		panic("incorrect argument")
	}
}

• Without the fix the above test program results are as follows:

  • Mac & Linux:
    • 1 -> Success
    • 2 -> Success
  • Windows:
    • 1 -> Failed
    • 2 -> Success

• With the fix the above test program results are as follows:

  • Mac & Linux:
    • 1 -> Success
    • 2 -> Success
  • Windows:
    • 1 -> Success
    • 2 -> Success

Release note

Fix file lock issue on windows

Additional information

Special notes for your reviewer

[marckhouzam]

Awesome! Thank you for this!

[vuil]

Thanks for the fix!