lockgate

Lockgate

Lockgate is a locking library for go.

• Classical interface:
  • 2 types of locks: shared and exclusive;
  • 2 modes of locking: blocking and non-blocking.
• File locks on the single host are supported.
• Kubernetes-based distributed locks are supported:
  • kubernetes locker is configured by an arbitrary kubernetes resource;
  • locks are stored in the annotations of the specified resource;
  • properly use native kubernetes optimistic locking to handle simultaneous access to the resource.

This library is used in the werf CI/CD tool to implement synchronization of multiple werf build and deploy processes running from single or multiple hosts using Kubernetes or local file locks.

If you have an Open Source project using lockgate, feel free to list it here.

Installation

go get -u github.com/flant/lockgate

Usage

In the following example a locker object instance is created using either NewFileLocker or NewKubernetesLocker constructor — user should select needed locker implementation. The rest of the sample uses lockgate.Locker interface to acquire and release locks.

import "github.com/flant/lockgate"

func main() {
	// Create Kubernetes based locker in ns/mynamespace cm/myconfigmap.
	// Initialize kubeDynamicClient from https://github.com/kubernetes/client-go.
        locker := lockgate.NewKubernetesLocker(                                                          
                kubeDynamicClient, schema.GroupVersionResource{                                         
                        Group:    "",                                                                    
                        Version:  "v1",                                                                  
                        Resource: "configmaps",                                                          
                }, "myconfigmap", "mynamespace",                                                              
        )
	
	// OR create file based locker backed by /var/locks/mylocks_service_dir directory
    	locker, err := lockgate.NewFileLocker("/var/locks/mylocks_service_dir")
	if err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: failed to create file locker: %s\n", err)
		os.Exit(1)
	}

        // Case 1: simple blocking lock

	acquired, lock, err := locker.Acquire("myresource", lockgate.AcquireOptions{Shared: false, Timeout: 30*time.Second}
	if err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: failed to lock myresource: %s\n", err)
		os.Exit(1)
	}

	// ...

	if err := locker.Release(lock); err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: failed to unlock myresource: %s\n", err)
		os.Exit(1)
	}

	// Case 2: WithAcquire wrapper

	if err := lockgate.WithAcquire(locker, "myresource", lockgate.AcquireOptions{Shared: false, Timeout: 30*time.Second}, func(acquired bool) error {
		// ...
	}); err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: failed to perform an operation with locker myresource: %s\n", err)
		os.Exit(1)
	}
	
	// Case 3: non-blocking

	acquired, lock, err := locker.Acquire("myresource", lockgate.AcquireOptions{Shared: false, NonBlocking: true})
	if err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: failed to lock myresource: %s\n", err)
		os.Exit(1)
	}

	if acquired {
		// ...
	} else {
		// ...
	}

	if err := locker.Release(lock); err != nil {
		fmt.Fprintf(os.Stderr, "ERROR: failed to unlock myresource: %s\n", err)
		os.Exit(1)
	}
}