wings/server/power.go

81 lines
2.9 KiB
Go

package server
import (
"context"
"github.com/pkg/errors"
"golang.org/x/sync/semaphore"
"os"
"time"
)
type PowerAction string
// The power actions that can be performed for a given server. This taps into the given server
// environment and performs them in a way that prevents a race condition from occurring. For
// example, sending two "start" actions back to back will not process the second action until
// the first action has been completed.
//
// This utilizes a workerpool with a limit of one worker so that all of the actions execute
// in a sync manner.
const (
PowerActionStart = "start"
PowerActionStop = "stop"
PowerActionRestart = "restart"
PowerActionTerminate = "kill"
)
// Checks if the power action being received is valid.
func (pa PowerAction) IsValid() bool {
return pa == PowerActionStart ||
pa == PowerActionStop ||
pa == PowerActionTerminate ||
pa == PowerActionRestart
}
// Helper function that can receive a power action and then process the actions that need
// to occur for it. This guards against someone calling Start() twice at the same time, or
// trying to restart while another restart process is currently running.
//
// However, the code design for the daemon does depend on the user correctly calling this
// function rather than making direct calls to the start/stop/restart functions on the
// environment struct.
func (s *Server) HandlePowerAction(action PowerAction, waitSeconds ...int) error {
if s.powerLock == nil {
s.powerLock = semaphore.NewWeighted(1)
}
// Determines if we should wait for the lock or not. If a value greater than 0 is passed
// into this function we will wait that long for a lock to be acquired.
if len(waitSeconds) > 0 && waitSeconds[0] != 0 {
ctx, _ := context.WithTimeout(context.Background(), time.Second*time.Duration(waitSeconds[0]))
// Attempt to acquire a lock on the power action lock for up to 30 seconds. If more
// time than that passes an error will be propagated back up the chain and this
// request will be aborted.
if err := s.powerLock.Acquire(ctx, 1); err != nil {
return errors.WithMessage(err, "could not acquire lock on power state")
}
} else {
// If no wait duration was provided we will attempt to immediately acquire the lock
// and bail out with a context deadline error if it is not acquired immediately.
if ok := s.powerLock.TryAcquire(1); !ok {
return errors.WithMessage(context.DeadlineExceeded, "could not acquire lock on power state")
}
}
// Release the lock once the process being requested has finished executing.
defer s.powerLock.Release(1)
switch action {
case PowerActionStart:
return s.Environment.Start()
case PowerActionStop:
return s.Environment.Stop()
case PowerActionRestart:
return s.Environment.Restart()
case PowerActionTerminate:
return s.Environment.Terminate(os.Kill)
}
return errors.New("attempting to handle unknown power action")
}