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// Copyright 2016 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.
package mutex
import (
"regexp"
"time"
"github.com/juju/errors"
)
var (
validName = regexp.MustCompile("^[a-zA-Z][a-zA-Z0-9-]*$")
)
// Releaser defines the Release method that is the only thing that can be done
// to a acquired mutex.
type Releaser interface {
// Release releases the mutex. Release may be called multiple times, but
// only the first call will release this instance of the mutex. Release is
// unable to release the mutex successfully it will call panic to forcibly
// release the mutex.
Release()
}
// Clock provides an interface for dealing with clocks.
type Clock interface {
// After waits for the duration to elapse and then sends the
// current time on the returned channel.
After(time.Duration) <-chan time.Time
// Now returns the current clock time.
Now() time.Time
}
// Spec defines the name of the mutex and behaviour of the Acquire function.
type Spec struct {
// Name is required, and must start with a letter and contain at most
// 40 letters, numbers or dashes.
Name string
// Clock must be provided and is exposed for testing purposes.
Clock Clock
// Delay defines how often to check for lock acquisition, for
// compatibility code that requires polling.
Delay time.Duration
// Timeout allows the caller to specify how long to wait. If Timeout
// is zero, then the call will block forever.
Timeout time.Duration
// Cancel if signalled will cause the Acquire method to return with ErrCancelled.
Cancel <-chan struct{}
}
// Acquire will attempt to acquire the named mutex. If the Timout value
// is hit, ErrTimeout is returned. If the Cancel channel is signalled,
// ErrCancelled is returned.
func Acquire(spec Spec) (Releaser, error) {
if err := spec.Validate(); err != nil {
return nil, errors.Trace(err)
}
var timeout <-chan time.Time
if spec.Timeout > 0 {
timeout = spec.Clock.After(spec.Timeout)
}
return acquire(spec, timeout)
}
// Validate checks the attributes of Spec for validity.
func (s *Spec) Validate() error {
if len(s.Name) > 40 {
return errors.NotValidf("Name longer than 40 characters")
}
if !validName.MatchString(s.Name) {
return errors.NotValidf("Name %q", s.Name)
}
if s.Clock == nil {
return errors.NotValidf("missing Clock")
}
if s.Delay <= 0 {
return errors.NotValidf("non positive Delay")
}
if s.Timeout < 0 {
return errors.NotValidf("negative Timeout")
}
return nil
}
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