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lock.go
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lock.go
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package lock
import (
"fmt"
"time"
"github.com/alevinval/vendor-go/pkg/log"
"github.com/rogpeppe/go-internal/lockedfile"
)
// Lock is used to ensure only one agent has permission to do certain operations.
// It relies on creating files
type Lock struct {
file *lockedfile.File
path string
warn string
period time.Duration
acquired bool
}
// New returns a Lock instance, it does not try to acquire the lock yet, so no
// file will be created until Acquire() is called.
func New(path string) *Lock {
return &Lock{
path: path,
period: time.Duration(1 * time.Second),
}
}
// WithWarn configures the warning message that will be printed on slow lock acquisition.
func (l *Lock) WithWarn(warn string) *Lock {
l.warn = warn
return l
}
// WithPeriod configures the polling period during lock acquisition, for purposes of
// printing the warning message.
func (l *Lock) WithPeriod(period time.Duration) *Lock {
l.period = period
return l
}
// Acquire attempts to lock the file. This operation blocks as long as needed
// until it can be acquired.
func (l *Lock) Acquire() (err error) {
if l.file, err = l.acquireLock(); err != nil {
return fmt.Errorf("cannot create lockfile: %w", err)
} else {
l.acquired = true
return nil
}
}
// Release the lock that was acquired.
func (l *Lock) Release() error {
if !l.acquired {
panic("attempted to release a lock that was never acquired")
}
return l.file.Close()
}
// acquireLock creates the lockfile in a go-routine and waits for the process to complete.
// If the process takes too long and warning is enabled, it will print a warning message.
func (l *Lock) acquireLock() (*lockedfile.File, error) {
fileCh := make(chan *lockedfile.File)
errCh := make(chan error)
go createLockFile(l.path, fileCh, errCh)
return waitForAcquire(fileCh, errCh, l.period, l.warn)
}
// waitForAcquire polls the channel and displays a warning message in case the lock
// operation takes longer than expected.
func waitForAcquire(
fileIn <-chan *lockedfile.File,
errIn <-chan error,
period time.Duration,
warnMsg string,
) (*lockedfile.File, error) {
warn := warnMsg != ""
for {
select {
case <-time.After(period):
if warn {
log.S().Warnf(warnMsg)
warn = false
}
case e := <-errIn:
return nil, e
case lock := <-fileIn:
return lock, nil
}
}
}
// createLockFile creates the lockfile and sends it to the output channel. This is done
// so we can poll the channel and show a warning message, rather than blocking indefinetely
// in case the lock is already acquired by someone else.
func createLockFile(path string, fileOut chan *lockedfile.File, errOut chan error) {
if file, err := lockedfile.Create(path); err != nil {
errOut <- err
} else {
fileOut <- file
}
}