github.com/axw/juju@v0.0.0-20161005053422-4bd6544d08d4/core/lease/claimer.go (about)

     1  // Copyright 2015 Canonical Ltd.
     2  // Licensed under the AGPLv3, see LICENCE file for details.
     3  
     4  package lease
     5  
     6  import (
     7  	"time"
     8  
     9  	"github.com/juju/errors"
    10  )
    11  
    12  // ErrClaimDenied indicates that a Claimer.Claim() has been denied.
    13  var ErrClaimDenied = errors.New("lease claim denied")
    14  
    15  // ErrNotHeld indicates that some holder does not hold some lease.
    16  var ErrNotHeld = errors.New("lease not held")
    17  
    18  // Claimer exposes lease acquisition and expiry notification capabilities.
    19  type Claimer interface {
    20  
    21  	// Claim acquires or extends the named lease for the named holder. If it
    22  	// succeeds, the holder is guaranteed to keep the lease until at least
    23  	// duration after the *start* of the call. If it returns ErrClaimDenied,
    24  	// the holder is guaranteed not to have the lease. If it returns any other
    25  	// error, no reasonable inferences may be made.
    26  	Claim(leaseName, holderName string, duration time.Duration) error
    27  
    28  	// WaitUntilExpired returns nil when the named lease is no longer held. If it
    29  	// returns any other error, no reasonable inferences may be made.
    30  	WaitUntilExpired(leaseName string) error
    31  }
    32  
    33  // Checker exposes facts about lease ownership.
    34  type Checker interface {
    35  
    36  	// Token returns a Token that can be interrogated at any time to discover
    37  	// whether the supplied lease is currently held by the supplied holder.
    38  	Token(leaseName, holderName string) Token
    39  }
    40  
    41  // Token represents a fact -- but not necessarily a *true* fact -- about some
    42  // holder's ownership of some lease.
    43  type Token interface {
    44  
    45  	// Check returns ErrNotHeld if the lease it represents is not held by the
    46  	// holder it represents. If trapdoorKey is nil, and Check returns nil, then
    47  	// the token continues to represent a true fact.
    48  	//
    49  	// If the token represents a true fact and trapdoorKey is *not* nil, it will
    50  	// be passed through layers for the attention of the underlying lease.Client
    51  	// implementation. If you need to do this, consult the documentation for the
    52  	// particular Client you're using to determine what key should be passed and
    53  	// what errors that might induce.
    54  	Check(trapdoorKey interface{}) error
    55  }